Latest ESO telbib papers

An Overabundance of Radio Active Galactic Nuclei in the SPT2349─56 Protocluster: Preheating the Intracluster Medium

First Author: Chapman, Scott C.
Instruments: ALMA_Band_6, ALMA_Band_7
ProgramIDs: 2018.1.00058.S, 2021.1.01313.S
BibCode: 2026ApJ..1000L..10C

Following the detection of a radio-loud active galactic nucleus (AGN) in the z = 4.3 protocluster SPT2349−56, we have obtained additional observations with the South African MeerKAT radio telescope in the S band (2.4 GHz) with the aim of further characterizing radio emission from amongst the ∼30 submillimeter galaxies (SMGs) identified in the structure. In addition to the previous radio-AGN, we newly identify two of the protocluster SMGs individually at 2.4 GHz as having a radio excess. Two of these radio-AGN are now known to be X-ray luminous AGN. Two additional members are also detected with radio emission consistent with their star formation rate (SFR). Archival MeerKAT Ultra-High Frequency (UHF; 816 MHz) observations further constrain luminosities and radio spectral indices of these five galaxies. The Australia Telescope Compact Array is used to detect and resolve the central two sources at 5.5 and 9.0 GHz finding elongated, bipolar jet-like morphologies. The excess radio luminosities range from L_1.4,rest = (1─20) × 10²⁵ W Hz⁻¹, ∼10─100× higher than expected from the SFRs, assuming the usual far-infrared─radio correlation. Of the known cluster members, only the SMG "N1" shows signs of AGN in any other diagnostics, namely a large and compact excess in ¹²CO(11─10) line emission. We compare these results to field samples of radio sources and SMGs. The overdensity of radio-loud AGN in the compact core region of the cluster may be providing significant heating to the recently discovered nascent intracluster medium in SPT2349−56.

Hiding behind a curtain of dust: Gas and dust properties of an ultra-luminous strongly-lensed z = 3.75 galaxy behind the Milky Way disc

First Author: Alcalde Pampliega, Belén
Instruments: ALMA_Band_3, ALMA_Band_4, ALMA_Band_6, ALMA_Band_7, FORS2, MUSE, nFLASH
ProgramIDs: 2023.1.00251.S, 111.24P0, 111.24UJ, 0113.F-9710, 0114.F-9703, 2015.1.00512.S, 2017.1.00303.S, 2018.1.00126.S, 2019.1.00245.S, 2021.2.00097.S
BibCode: 2026A&A...706A.174A

We present a detailed analysis of J154506, a strongly lensed submillimetre galaxy (SMG) behind the Lupus-I molecular cloud, and a characterisation of its physical properties using a combination of new and archival data, including VLT/MUSE and FORS2 optical data. We identify two high-significance (S/N > 5) emission lines at 97.0 and 145.5 GHz, corresponding to CO(4-3) and CO(6-5), respectively, in spectral scans from the Atacama Compact Array (ACA) and the Large Millimetre Telescope (LMT), as well as the [CII] 158 μm fine-structure line at 400 GHz observed with the Atacama Pathfinder Experiment (APEX). These detections yield a spectroscopic redshift of z_spec = 3.7515 ± 0.0005. We also report the detection of [CI], HCN(4-3), and two H₂O⁺ transitions, further confirming the redshift and providing insights into the physical properties of J154506. By modelling sub-arcsecond resolution (0.75″) ALMA Band 6 and 7 continuum data in the uv-plane, we derive an average magnification factor of 6.0 ± 0.4, and our analysis reveals a relatively cold dust (38 K) in a starburst galaxy (∼ 900 M_⊙ yr⁻¹) with a high intrinsic dust mass (∼ 2.5 × 10⁹ M_⊙) and infrared (IR) luminosity (∼ 6 × 10¹² L_⊙). Non-local thermodynamic equilibrium radiative transfer modelling of the joint dust spectral energy distribution (SED) and CO line excitation suggests the dust continuum emission is primarily associated with relatively diffuse regions with molecular gas densities of 10²−10⁴ cm⁻³, rather than compact, high-pressure environments typical of extreme starbursts or active galactic nuclei (AGNs). This interpretation is supported by the close-to-unity ratio between the dust and gas kinetic temperatures, which argues against highly energetic heating mechanisms. The CO excitation ladder peaks close to CO(5-4) and is dominated by slightly denser molecular gas. Our results underscore the unique power of far-IR and submillimetre observations to both uncover and characterise scarce, strongly lensed, high-redshift galaxies, even when they are obscured by foreground molecular clouds.

Fast rotations in galaxies at cosmic noon indicate central concentration of stars, dark matter, or massive black holes

First Author: Roman-Oliveira, Fernanda
Instruments: ALMA_Band_3, ALMA_Band_4, ALMA_Band_6
ProgramIDs: 2016.1.01426.S, 2017.1.00413.S, 2017.1.00471.S, 2017.1.01659.S
BibCode: 2026MNRAS.546ag213R

The rotation curves of regularly rotating disc galaxies are a unique probe of the gravitational potential and dark matter distribution. Until recently, matter decomposition of rotation curves at

$z\gt0.5$

was challenging, not only due to the lack of high resolution kinematic data but also of both suitable photometry to accurately trace the stellar surface density and spatially-resolved sub-mm observations to trace the cold gas distribution. In this paper, we analyse three galaxies from the Archival Large Programme to Advance Kinematic Analysis (ALPAKA) sample, combining highly resolved cold gas observations from the Atacama Large Millimeter/submillimeter Array (ALMA) with rest-frame near-infrared imaging from James Webb Space Telescope (JWST) to investigate their dynamical properties and constrain their dark matter haloes. The galaxies, initially classified as regularly rotating discs based on ALMA observations alone, appear in JWST as extended and symmetric stellar discs with spiral arms. Our dynamical models reproduce the rotation of the discs in the outer parts well, but they systematically underpredict the inner rotation velocities, revealing a deficit of central mass relative to the data. This discrepancy indicates either an underestimation of the bulge masses due to variations in the stellar mass-to-light ratio or dust attenuation or the presence of overmassive black holes. Alternatively, it may suggest departures from standard dark-matter halo profiles, including enhanced central concentrations.

ALMA FACTS. III. High-resolution CO(2─1)/CO(1─0) Maps of Twelve Nearby Galaxies

First Author: Lee, Amanda M.
Instruments: ALMA_Band_3, ALMA_Band_6
ProgramIDs: 2012.1.00650.S, 2015.1.00925.S, 2015.1.00956.S, 2017.1.00886.L, 2018.1.01651.S, 2022.1.00360.S
BibCode: 2026ApJ..1001...33L

We present early results from a high-resolution analysis (∼100─200 pc) of the CO(2─1)/CO(1─0) line ratio in 12 nearby galaxies. We use new Atacama Large Millimeter/submillimeter Array (ALMA) CO(1─0) observations from the Fundamental CO(1─0) Transition Survey (FACTS), and re-imaged CO(2─1) data from PHANGS. We make empirical classifications based on the optical and molecular gas morphologies, which show clear systematic trends in the variation of R₂₁ as a function of galactic structure. The sample includes barred, unbarred, and flocculent galaxies. The barred spiral galaxies follow a general trend when the gas exists significantly: R₂₁ is high in the center, low along the bar, increases at the bar ends, and then lowers beyond the bar end or flattens in the outer parts of the disk. The structure dependence suggests the importance of galactic dynamics on molecular gas evolution, and consequently on star formation, in galaxies. R₂₁ fluctuates in the spiral arms for both barred and unbarred galaxies. Areas around HII regions in some cases appear to show more high-ratio gas. Together, R₂₁ varies systematically as a function of galactic structure, dynamics, and star formation activity.

Tentative Detection of Neutral Gas in a Little Red Dot at z = 4.46

First Author: Akins, Hollis B.
Instruments: ALMA_Band_3, ALMA_Band_4, ALMA_Band_5
ProgramIDs: 2024.1.01085.S
BibCode: 2026ApJ...997..218A

JWST has revealed a population of broad-line active galactic nuclei at z > 4 with remarkably red colors, so-called "Little Red Dots" (LRDs). Ubiquitous Balmer breaks suggest that they harbor old stellar populations in massive, compact host galaxies. We present Atacama Large Millimeter/submillimeter Array observations of three LRDs at z = 3.10, 4.46, and 7.04, targeting molecular and neutral gas via CO(7─6) and [C I](2─1), respectively. We do not detect CO in any target, placing conservative limits on the host molecular gas mass of ≲(1─5) × 10¹⁰ M_⊙. We report the tentative (∼3.5σ) detection of the [C I](2─1) line in A2744-45924 (z = 4.46), one of the brightest known LRDs. The [C I] line is narrow (FWHM ∼ 80 km s⁻¹), implying a dynamical mass ≲10¹⁰ M_⊙, adopting conservative limits for the size of the galaxy. The dynamical mass limit is significantly lower than expected from the local M_BH─M_dyn relation, and is an order of magnitude below the stellar mass derived from spectral energy distribution fitting, potentially supporting a nonstellar origin of the Balmer break. These results, while tentative, paint a picture of LRDs that is markedly different than typical high-z quasars, which live in massive, gas-rich, and actively star-forming host galaxies.

ALMA 873 µm polarization observations of the PDS 70 disk

First Author: Liu, Hauyu Baobab
Instruments: ALMA_Band_3, ALMA_Band_4, ALMA_Band_6, ALMA_Band_7
ProgramIDs: 2019.1.01619.S, 2022.1.01477.S
BibCode: 2026A&A...708A..95L

At a 112.4 pc distance, the PDS 70 protoplanetary disk is a rare case that has been confirmed to host two accreting planets. This makes it the most important laboratory for studying dust growth in the context of planet formation. Here we present the first deep full polarization observations at a wavelength of 873 µm. We detected ∼1─2.5% linear polarization over the bulk of the ~55─100 AU (sub)millimeter ring. The polarization position angles align preferentially with the projected minor axis of the disk. The standard interpretation is that the observed polarization is caused by dust self-scattering, with a maximum dust grain size of ~100 µm. On ≳10 AU scales, which can be resolved by the presented 873─3075 µm observations, the ring is marginally optically thick at the 873 µm wavelength. Using Monte Carlo radiative transfer simulations, we found that an azimuthally asymmetric, marginally optically thick ring with a maximum dust grain size of ∼87 µm can reproduce the observed 873 µm polarization position angles and percentages. This study indicates that the coagulation of ice-coated dust in the protoplanetary disk may be limited by fragmentation or bouncing.

Moonlit sky polarization patterns from Cerro Paranal

First Author: Pereira, B.
Instruments: FORS2
ProgramIDs: 106.21L9
BibCode: 2026A&A...706A.325P

We investigated the polarization patterns from the moonlit sky as observed from the European Southern Observatory at Cerro Paranal. The moonlit sky background can be significant in astronomical observations and thus be a source of contamination in polarimetric studies. Based on sky observations during full Moon with FORS2 in imaging polarimetric mode, we measured the polarization degree and intensity at different wavelengths and scattering angles from the Moon, and we compared them to theoretical and phenomenological single- and multiple-scattering models. Single-scattering Rayleigh models are able to reproduce the wavelength dependence of the polarization as long as strong depolarization factors that increase with wavelength are introduced. Intensity data, however, require the inclusion of single Mie scattering from larger aerosol particles. The best models that simultaneously fit polarization and intensity data are a combination of the two single-scattering processes, Rayleigh and Mie, plus an unpolarized multiple-scattering component. Both Mie and multiple scattering become more dominant at longer wavelengths. Other factors such as cloud depolarization and the sunlight contribution at twilight were also investigated. The present study underscores the importance of accounting for moonlight scattering to enhance the accuracy of polarimetric observations of astronomical targets.

Confirmation of a Non-Transiting Planet in the Habitable Zone of the Nearby M Dwarf L 98-59

First Author: Schwarz, Paul I.
Instruments: ESPRESSO, HARPS
ProgramIDs: 198.C-0838, 1102.C-0339, 0102.C-0525, 1102.C-0958, 1104.C-0350, 1102.C-0744, DataDoiProID
BibCode: 2026AN....34770059S

Only 40 exoplanetary systems with five or more planets are currently known. These systems are crucial for our understanding of planet formation and planet-planet interaction. The M dwarf L 98-59 has previously been found to show evidence of five planets, three of which are transiting. Our aim is to confirm the fifth planet in this system and to refine the system characteristics namely minimum masses, radii and the orbital parameters of the planets around L 98-59. We reanalysed RV and activity data from HARPS and ESPRESSO alongside TESS and HST transit data using a joint model. The parameter space was sampled using the dynesty nested sampler. We confirm the previously known fifth planet in the system's habitable zone with an orbital period of ${23.069}_{-0.082}^{+0.081}\kern0.5em \mathrm{days}$, a minimum mass of ${2.97}_{-0.48}^{+0.46}{M}_{\oplus }$ and an equilibrium temperature of 284 K. We find an additional planet candidate in the RV data with an orbital period of $1.736\kern0.5em {15}_{-0.000\kern0.5em 76}^{+0.000\kern0.5em 74}\ \mathrm{days}$ and a minimum mass of $0.58\pm 0.12{M}_{\oplus }$. This candidate (L 98-59.06) has a statistical significance between $2.9\kern0.6em \sigma$ and $4.2\kern0.22em \sigma$, details depending on the modelling of stellar variability. Moreover, we present evidence for a stellar rotation period of ${76.6}_{-4.2}^{+4.1}\ \mathrm{days}$.

Hidden in Plain Sight II: Characterizing the Luminous Companion to κ Velorum with VLTI/GRAVITY

First Author: Rowan, D. M.
Instruments: GRAVITY, UVES
ProgramIDs: 194.C-0833, 114.274C
BibCode: 2026PASP..138b4203R

κ Vel (Markeb, HD 81188, 天社五) is one of the brightest stars in the Southern sky and has long been known to be a single-lined spectroscopic binary. The binary mass function is large, f(M) = 1.15 M_⊙, suggesting that the bright (V = 2.5) B2IV star may host a dark, compact object companion. We use VLTI/GRAVITY observations to definitively test this possibility by directly resolving the binary. We detect a main sequence B star companion and rule out the compact object scenario. By combining the relative astrometric orbit and archival radial velocities, we report an updated precise characterization of the orbit (period P = 116.795 ± 0.002 days, eccentricity e = 0.1764 ± 0.0004, inclination i = 74 .° 04 ± 0 .° 01) and estimate the masses of the B stars. Using the original Hipparcos parallax measurement ϖ = 6.05 ± 0.48 mas, we find M1=10−2+4M⊙ and M₂ = 6.9 ± 1.0 M_⊙. The uncertainties on the masses are primarily driven by the uncertain parallax, which we find is likely biased by the orbital motion. We use an archival UVES spectrum and MIST evolutionary tracks to refine our mass estimates. Finally, we discuss how interferometry and high-contrast imaging may be used to characterize other candidate star+compact object binaries, including those that will be discovered with Gaia DR4, as part of a larger effort to uncover the hidden population of black holes in the Milky Way.

Substellar population of the young massive cluster RCW 36 in Vela

First Author: do Brito do Vale, A. R. G.
Instruments: HAWKI, SOFI
ProgramIDs: 0104.C-0369, 080.C-0836
BibCode: 2026A&A...706A.149D

Context. The shape of the initial mass function (IMF) remains a fundamental yet contentious topic in the study of stellar formation and evolution. It is imperative to understand the potential variability of the IMF across different young regions. This study examines the IMF within the young massive cluster RCW 36 situated in the Vela Molecular Ridge, comparable with the Orion Nebula Cluster in terms of stellar surface density. Aims. The primary objective of this research is to construct the most comprehensive census of the stellar population in RCW 36 to date and determine the first ever IMF and star to brown dwarf (BD) ratio for the cluster. Methods. We used state-of-the art observational techniques, drawing on new GLAO observations conducted with HAWK-I/VLT in addition to archival data from 2MASS, SOFI/NTT, and new kinematics from Gaia DR3. To enhance photometric accuracy and source extraction, we employed DENEB, an advanced deep learning algorithm capable of removing the complex filamentary nebula in our images. Statistical comparisons of color-magnitude diagrams were performed between RCW 36 and a control field, also obtained using HAWK-I under the same mode, to assign membership weights for the sources in our field. Mass estimates to individual sources were also derived through comparison with model isochrones in order to determine the IMF using the membership weights. Results. We found a new distance of 954 ± 40 pc. We determined the IMF for RCW 36 down to ~0.03 M_⊙, characterized by a broken power law (dN/d M ∝ M^−α) with α = 1.62 ± 0.03 (0.20 M_⊙ −20 M_⊙) and α = 0.46 ± 0.14 (0.03 M_⊙─0.20 M_⊙). We also determined the star-BD ratio to be 2─5, in agreement with other Galactic clusters. Lastly, through a study of the differences in the IMF within and outside 0.2 pc and the cumulative mass distributions for low-mass and intermediate to high-mass sources, we also detected signs of possible mass segregation within RCW 36, which should be primordial. Conclusions. RCW 36 shares many characteristics with other young massive clusters, such as a shallower than Salpeter high-mass slope and the possibility of mass segregation. The flatter lower-mass regime of the IMF is similar to most Galactic clusters. The star-BD ratio is also in line with the observed values in other clusters, independent of their inherent properties.

Coordinated space-and ground-based monitoring of accretion bursts in a protoplanetary disc: The orbital and accretion properties of DQ Tau

First Author: Alqubelat, Hala
Instruments: UVES, XSHOOTER
ProgramIDs: 082.C-0218, 114.2799, 114.27MG
BibCode: 2026A&A...706A.228A

Multiplicity in pre-main-sequence (PMS) systems shapes circumstellar and circumbinary discs, often resulting in morphological features such as inner cavities, spiral arms, and gas streamers that facilitate mass transfer between the disc and stars. Consequently, accretion in eccentric close binaries is highly variable and synchronized with their orbits, producing distinct bursts near periastron passages. In this study, we examine the orbital and accretion properties of the eccentric Classical T-Tauri binary star DQ Tau using medium- to high-resolution spectroscopy obtained using the Very Large Telescope (VLT) X-shooter and UVES instruments. The data have been taken at the time of a monitoring of the inner disc chemistry with JWST, and the results of our analysis are needed for a correct interpretation of the JWST data. We refine the orbital parameters of the system and report an increment in the argument of periastron of ~30º. This apsidal motion can be caused by the massive disc acting as a third body in the system. We also explore the possibility that the resulting apsidal motion is caused by a still not-detected additional (sub-)stellar companion. In this case, we estimate a lower limit of ~15 M_J for the mass of this putative companion at the cavity edge (a = 3a_bin). We investigate the accretion of the primary and secondary stars in the system using the Ca II 849.8 nm emission line. We observe the primary accretes more at the periastron compared to its previous quiescent phases. The secondary dominates the accretion at post-periastron phases. Additionally, we report an elevated L_acc at apastron, possibly due to the interaction of the stars with irregularly shaped structures near their closest approach to the circumbinary disc. Finally, we derive the accretion luminosity of each star across the disentangled epochs and compare the results to those derived by the UV excess, finding a good overall agreement. The individual L_acc values can be used as an input for the chemical models.

A Unified Photometric Redshift Calibration for Weak Lensing Surveys Using the Dark Energy Spectroscopic Instrument

First Author: Lange, J. U.
Instruments: OMEGACAM, VIRCAM
ProgramIDs: 177.A-3018, 179.A-2004, 177.A-3016, 177.A-3017
BibCode: 2026ApJ...998..263L

The effective redshift distribution n(z) of galaxies is a critical component in the study of weak gravitational lensing. Here, we introduce a new method for determining n(z) for weak lensing surveys based on high-quality redshifts and neural-network-based importance weights. Additionally, we present the first unified photometric redshift calibration of the three leading stage-III weak lensing surveys, the Dark Energy Survey (DES), the Hyper Suprime-Cam (HSC) survey, and the Kilo-Degree Survey (KiDS), with state-of-the-art spectroscopic data from the Dark Energy Spectroscopic Instrument (DESI). We verify our method using a new, data-driven approach and obtain n(z) constraints with statistical uncertainties of the order of σz̄∼0.01 and smaller. Our analysis is largely independent of previous photometric redshift calibrations and, thus, provides an important cross-check in light of recent cosmological tensions. Overall, we find excellent agreement with previously published results on the DES Y3 and HSC Y1 data sets, while there are some differences on the mean redshift with respect to the previously published KiDS-1000 results. We attribute the latter to mismatches in photometric noise properties in the COSMOS field compared to the wider KiDS self-organizing map-gold catalog. At the same time, the new n(z) estimates for KiDS do not significantly change estimates of cosmic structure growth from cosmic shear. Finally, we discuss how our method can be applied to future weak lensing calibrations with DESI data.

The Type Ia supernova 2021hem: A 2003fg-like event in an apparently hostless environment

First Author: Bose, S.
Instruments: SOFI
ProgramIDs: 1103.D-0328
BibCode: 2026A&A...706A.252B

We report observations of a Type Ia supernova (SN Ia) 2021hem that was discovered within 48 hours of last nondetection and is located in an apparently hostless environment. With a peak absolute B-band magnitude of M_{B, max} = −19.96 ± 0.29 mag, SN 2021hem lies at the luminous end of the SNe Ia distribution. Its near-infrared and i-band light curves lack the secondary maximum, which is otherwise ubiquitous to normal and 1991T-like SNe Ia. Instead, these properties cause SN 2021hem to closely resemble 2003fg-like events. The slowly evolving light curves (characterized by ∆m₁₅(B) = 1.02 ± 0.02 mag; s_BV = 0.94 ± 0.05) and the earliest spectrum showing C IIλ6580 and λ7235 absorption lines further support this classification. Other spectroscopic features, including Si II line diagnostics, resemble those of normal SNe Ia. A fit of a fireball model to the early-time light curves yields a time of first light of t_first = −16.43^+0.45_−0.38 t first = − 16 . 43 − 0.38 + 0.45 days relative to B-band maximum. The first photometric detection occurs 1.51^+0.45_−0.38 1 . 51 − 0.38 + 0.45 days before the onset of fireball-like flux rise. This early emission, together with the intrinsic (g − r)₀ color, is inconsistent with circumstellar or companion interaction. Instead, shallow ⁵⁶Ni mixing or an asymmetric ⁵⁶Ni distribution offers a plausible explanation for the delayed onset of the fireball flux rise, while a double-detonation scenario with a thin helium shell remains a less likely alternative. Notably, SN 2021hem represents the fifth known 2003fg-like SN that has early-time activity or excess flux emission. The estimated mass of radioactive ⁵⁶Ni synthesized in SN 2021hem is 1.00 ± 0.09 M_⊙. Deep GTC imaging obtained 2.5 years after the explosion, with an estimated limiting magnitude of m_{lim, r} = 24.4 mag and a surface-brightness limit of μ_{lim, r} = 26.3 mag arcsec⁻², revealed no coincident host. Most faint dwarf and ultradiffuse galaxies (UDGs) are therefore ruled out. Alternatively, if the nearest plausible AGN host galaxy located at a projected distance of 104 kpc is assumed, the progenitor would need to be a hypervelocity star ejected at ≍2200 km s⁻¹ from the host by AGN interaction. A faint diffuse feature ≍6 kpc from the SN site has also been detected in the GTC image, and its surface brightness is within the limits of UDGs. It is unclear whether it is a galaxy and is associated with SN 2021hem, however. Based on its large normalized directional light distance (d_DLR ≍ 3 − 4) from the SN and its unusual elongation, the probability that this is the candidate host galaxy of SN 2021hem is low. These results identify SN 2021hem as one of the strongest candidates for a hostless SN Ia and underscore the diversity of luminous slowly evolving 2003fg-like explosions and the wide range of environments in which they may occur.

Kinematics of young stellar objects in NGC 2024 based on infrared proper motions

First Author: Rottensteiner, Alena
Instruments: VIRCAM
ProgramIDs: 60.A-9285, 198.C-2009, 179.A-2010
BibCode: 2026A&A...706A.210R

The most recently formed young stellar objects (YSOs) in active star-forming regions are excellent tracers of their parent cloud motion. Their positions and dynamics provide insights into cluster formation and constrain kinematic decoupling timescales between stars and gas. However, because of their strong extinction and young age, embedded YSOs are mainly visible at infrared wavelengths, and are thus absent from astrometric surveys such as Gaia. We measured the proper motions of 6769 sources toward the NGC 2024 cluster in the Flame Nebula (d ~ 420 pc) using multi-epoch near-infrared observations from three ESO public surveys: VISIONS, VHS, and the VISTA/VIRCAM science verification program. Cross-validation of our results with Gaia using optically visible stars shows excellent agreement, with uncertainties on the same order of magnitude. For 362 YSO candidates identified from the literature, we derived proper motions on the order of <5 mas yr⁻¹ with mean measurement uncertainties of 0.22 mas yr⁻¹, or 0.44 km s⁻¹. This is the first homogeneous proper motion measurement of this quality for more than half of these stars. For Class I and flat-spectrum sources, our results provide a >13-fold increase in available proper motion measurements. We analyzed the positional and kinematic differences between YSO classes and confirmed a previously reported inside-out age segregation from younger to older stars, likely driven by an outward movement of older stars. No evidence of prolonged hierarchical assembly was found. Instead, the results support a rapid (<1 Myr) cluster collapse into a centrally concentrated system. This scenario also accounts for the observed slightly higher 1D velocity dispersion of Class I sources relative to Class flat objects. YSO radial velocities generally align with the gas velocities measured from the molecular transitions of ¹²CO(3 − 2), HNC(1 − 0), HCN(1 − 0), and show a weaker correlation with N₂H⁺(1 − 0). Some Class II and III objects already appear to be decoupling.

Photometric and spectroscopic variability of the blue supergiant ρ Leo

First Author: Checha, V. A.
Instruments: HARPS
ProgramIDs: 60.A-9036, DataDoiProID
BibCode: 2026A&A...706A.200C

Context. The post-main-sequence evolution of massive stars remains poorly understood, particularly in the case of blue supergiants. As key drivers of the dynamical and chemical evolution of galaxies, massive stars warrant detailed investigation during this complex evolutionary stage. Hot supergiants exhibit pronounced photometric and spectroscopic variability, typically in the form of quasi-periodic rather than strictly periodic variations. Aims. We investigated the variability patterns of the evolved B-type star ρ Leo to determine its properties, identify the underlying physical processes, and constrain its evolutionary stage. We combined extensive long-term datasets of spectroscopic and photometric observations from various sources. These include data from the TESS and Kepler space telescopes, as well as observations from the 1.5 m telescope in Estonia. Methods. We analysed the data using the generalized Lomb─Scargle periodogram, the Lomb─Scargle periodogram with pre-whitening, and the weighted wavelet Z-transform. To determine the fundamental parameters of ρ Leo, we fitted synthetic line profiles computed with the FASTWIND code to the HARPS spectrum. We used the ZPEKTR code to infer the stellar rotation inclination angle. Results. The He I 6678.151 Å line profile exhibits significant changes in radial velocity and, consequently, in its moment values. We identify a set of periods and harmonics ranging from ∼0.8 to ∼35 days. Some periods remain nearly constant, while others appear and disappear from one observing season to another. A comparison of spectroscopic and photometric data, along with the shape of the phase curves, helps to constrain the nature of several periods. In particular, the ∼11-day period is attributed to stellar rotation, while the ∼17-day period is associated with radial pulsations. Conclusions. Despite their quasi-periodic nature, most periods are observable across multiple observing seasons. Based on the fairly wide range of detected periods, ρ Leo is likely on the blue loop of its evolution, following the red supergiant stage.

The hydrogen-free circumstellar interaction in the Type Ib supernova 2021efd: A clue to the mechanism of the helium-layer stripping

First Author: Pyykkinen, N.
Instruments: FORS2
ProgramIDs: 105.20DF, 108.2282
BibCode: 2026A&A...706A.183P

Context. Stripped-envelope supernovae (SESNe), including Type IIb, Ib, and Ic supernovae (SNe), originate from the explosions of massive stars whose outer envelopes have been largely removed during their lifetimes. The main stripping mechanism for the hydrogen (H) envelope in the progenitors of SESNe is often considered to be interaction with a binary companion, but the stripping mechanism for the helium (He) layer is unclear. Aims. We study the process of the He-layer stripping in the progenitors of SESNe. This is closely related to the origin of their diverse observational properties. Methods. We conducted photometric and spectroscopic observations of the Type Ib SN 2021efd, which shows signs of interaction with H-free circumstellar material (CSM). At early phases, its photometric and spectroscopic properties resemble those of typical Type Ib SNe. Around 30 days after the r-band light curve (LC) peak until at least ∼770 days, the luminosity of the multiband LCs is higher than that of regular SESNe and has at least three distinct peaks. The LC evolution is similar to that of SN 2019tsf, whose previously unpublished spectrum at 400 days is also presented here. The nebular spectrum of SN 2021efd shows narrow emission lines (∼1000 km s⁻¹) in various species, such as O I, Ca II, Mg II, He I, [O I], [Ca II], and [S II]. Based on the observations, we studied the properties of the ejecta and CSM of SN 2021efd. Results. Our observations suggest that SN 2021efd is a Type Ib SN that interacts with the CSM with the following parameters: The estimated ejecta mass, explosion energy, and ⁵⁶Ni mass are 2.2 M_⊙, 9.1 × 10⁵⁰ erg, and 0.14 M_⊙, respectively, and the estimated CSM mass, composition, and distribution are at least a few times 0.1 M_⊙, H free, and clumpy, respectively. Based on the estimated ejecta properties, we conclude that this event is a transitional SN whose progenitor was experiencing He-layer stripping at the epoch of the explosion and was on the way to becoming a carbon-oxygen star (as the progenitors of Type Ic SNe) from a He star (as the progenitors of Type Ib SNe). The estimated CSM properties suggest that the progenitor had some episodic mass ejections at a rate of ∼5 × 10⁻³ − 10⁻² M_⊙ yr⁻¹ for the last decade and slightly lower before this final phase at least from ∼200 years before the explosion for the assumed CSM velocity of 100 km s⁻¹. For the case of ∼1000 km s⁻¹, the necessary mass-loss rate would be higher by a factor of ten, and the timescales would be shorter by a factor of ten.

Deep Andromeda JCMT SCUBA-2 Observations. The Submillimeter Maps and Giant Molecular Clouds

First Author: Jiao, Sihan
Instruments: ALMA_Band_3
ProgramIDs: 2019.1.01847.S
BibCode: 2026ApJS..282...39J

We have carried out unprecedentedly deep, nearly confusion-limited JCMT SCUBA-2 mapping observations on the nearest spiral galaxy, M31 (Andromeda). The 850 μm image with a ∼50 pc resolution yields a comprehensive catalog of 383 giant molecular clouds (GMCs) that are associated with the spiral arms. In addition, it unveiled a population of 189 compact interarm GMCs in M31, which are mostly unresolved or marginally resolved. The masses of all these GMCs are in the range of 2 × 10⁴─6 × 10⁶ M_⊙; the sizes are in the range of 30─130 pc. They follow a mass─size correlation, M ∝ R_c^2.5. The interarm GMCs are systematically less massive, more diffuse, colder, and have lower star formation efficiency (SFE) than on-arm GMCs. Moreover, within individual spatially resolved on-arm and off-arm M31 GMCs, the SFE is considerably lower than the SFE in molecular clouds in main-sequence and green valley galaxies. Follow-up investigations on M31 GMCs may provide clues for how star formation may be quenched in galactic environments. Finally, we reconstrained the dust opacity spectral index β in the M31 galaxy by combining our new JCMT observations with archival Herschel and Planck data and found that the radial variation in β may not be as large as has been proposed by previous studies.

Does the solar oxygen abundance change over the solar cycle?: An investigation into activity-induced variations in the O I infrared triplet

First Author: Pietrow, A. G. M.
Instruments: FEROS
ProgramIDs: 60.A-9700
BibCode: 2026A&A...706L..11P

The determination of the solar oxygen abundance remains a central problem in astrophysics because its accuracy is limited not only by models, but also by systematics. While many of these factors have been thoroughly characterized, the effect of the solar activity cycle has remained unexplored so far. Because of its relative strength and accessibility, the O I infrared triplet is typically the primary choice for abundance studies. Previous investigations have shown, however, that abundances inferred from this triplet tend to be higher than expected on active stars, but no such overabundance effect is observed for the much weaker forbidden O I 6300 Å line. This raises the question of whether a similar trend can be found for the Sun. To address this question, we analyzed synoptic disk-integrated Sun-as-a-star datasets of two decades from the FEROS, HARPS-N, PEPSI, and NEID spectrographs with a focus on the infrared triplet (7772, 7774, and 7775 Å) and the forbidden O I 6300 Å line. The excellent signal-to-noise ratio of the PEPSI observations allowed us to detect a weak but significant variation in the equivalent widths of the infrared triplet that corresponds to an abundance difference of about 0.01 dex between activity minimum and maximum. This value is significantly lower than the typical uncertainties on the solar oxygen abundance. No comparable trend is found in the other datasets because the scatter is higher. Based on these results, we conclude that within the typical uncertainties presented in other works, we can assume the inferred solar oxygen abundance to be stable throughout the solar cycle, but that this effect might be significant for other more active stars.

Hubble's Multiyear Search for Exospheres in the TRAPPIST-1 System Reveals Frequent Microflares

First Author: Berardo, David
Instruments: FORS2
ProgramIDs: 0102.C-0635
BibCode: 2026ApJ...998L..31B

Lyα observations provide a powerful probe of stellar activity and atmospheric escape in exoplanetary systems. We present here an analysis of 109 Hubble Space Telescope (HST)/Space Telescope Imaging Spectrograph (STIS) orbits monitoring the TRAPPIST-1 system between 2017 and 2022, covering three to five transits for each of its seven planets. We rule out transit depths ≳30%, prompting a revision of atmospheric escape rates, with upper limits O(10)× larger than previously reported (e.g., O(70) Earth-ocean-equivalent hydrogen content per Gyr for planet b, consistent with claims that it is airless). The transit depth upper limits are ∼3 times larger than expected from the photon noise owing to a large baseline scatter, which we link to TRAPPIST-1's intrinsic Lyα variability from frequent "microflares." While JWST's near-infrared observations have shown that ∼10³⁰erg flares occur every ∼6 hr, we identify ∼10²⁹erg flares on subhour timescales in both HST/STIS and Very Large Telescope g' observations. The far-UV and optical amplitudes (∼400% vs. ∼3%, respectively) for flares with similar waiting times indicate flare temperatures of 9700 −2400+1500 K over 0.017 −0.007+0.03 % of the stellar disk. Finally, our multiyear baseline reveals a variability with P = 3.27 ± 0.04 days—the first independent validation of TRAPPIST-1's 3.3-day rotation period.

Resolved H II Regions in NGC 253: Ionized Gas Structure and Suggestions of a Universal Density─Surface Brightness Relation

First Author: McClain, Rebecca L.
Instruments: MUSE
ProgramIDs: 108.2289, 0102.B-0078
BibCode: 2026ApJ...998..166M

We use the full-disk Very Large Telescope/MUSE mosaic of NGC 253 to identify 2492 H II regions and study their resolved structure. With an average physical resolution of 17 pc, this is one of the largest samples of highly resolved spectrally mapped extragalactic H II regions. Regions of all luminosities exhibit a characteristic emission profile described by a double Gaussian with a marginally resolved or unresolved core with radius < 10 pc surrounded by a more extended halo of emission with radius = 20─30 pc. Approximately 80% of the emission of a region originates from the halo component. As a result of this compact structure, the luminosity─radius relations for core and effective radii of H II regions depend sensitively on the adopted methodology. Only the isophotal radius yields a robust relationship in NGC 253, but this measurement has an ambiguous physical meaning. We invert the measured emission profiles to infer density profiles and find central densities of n_e ≍ 10─100 cm⁻³. In the brightest regions, these agree well with densities inferred from the [S II] λλ6716, 6730 doublet. The central density of H II regions correlates well with the surface brightness within the effective radius. We show that this same scaling relation applies to the recent MUSE + Hubble Space Telescope catalog for 19 nearby galaxies. We also discuss potential limitations, including completeness, impacts of background subtraction and spatial resolution, and the generality of our results when applied to other galaxies.

Detailed abundance determination of metal-poor stars with X-Shooter ─ I. Unusual chemistry in halo stars

First Author: Lowe, Benjamin D. C.
Instruments: XSHOOTER
ProgramIDs: 113.26N5
BibCode: 2026MNRAS.546ag170L

We present a detailed chemical analysis study of 16 candidate metal-poor stars, previously identified with 2dF+AAOmega, using X-Shooter spectra and the Korg 1D local thermodynamic equilibrium spectral synthesis code. We confirm the earlier metallicity estimates and reveal six extremely metal-poor (

$\left[\rm {Fe/H}\right]< -3$

) stars in the current sample. Two of these stars, including the most metal poor at

$\left[\rm {Fe/H}\right]= -3.89 \pm 0.07$

, are kinematically associated with the Gaia─Sausage─Enceladus (GSE) accretion event, increasing the number of known GSE stars with

$\left[\rm {Fe/H}\right]< -3.5$

to eight. From the X-Shooter spectra we determine abundances for 16 elements, with the element-to-iron abundance ratios generally consistent with high-resolution studies of Galactic halo stars. Within the sample, we identify three peculiar stars: the first is a GSE nitrogen enhanced metal-poor (

$\left[\rm {N/Fe}\right] = 1.60 \pm 0.10$

and

$\left[\rm {C/Fe}\right] = 0.23 \pm 0.08$

) star with unusually high Na (

$\left[\rm {Na/Fe}\right] = 2.26 \pm 0.07$

) and Li (

$\rm {A(Li)_{3DNLTE}} = 1.90 \pm 0.08$

) abundances, but lacking enhancements in

$\left[\rm {Al/Fe}\right]$

$\left[\rm {Mg/Fe}\right]$

. The second is a halo r-II star significantly enhanced in Sr (

$\left[\rm {Sr/Ba}\right] = 0.39 \pm 0.08$

), suggesting mixture of r-process and s-process enrichment, uncommon for r-II stars. Whilst the third is a halo star very depleted in N (

$\left[\rm {N/Fe}\right] < -1.11$

), with low C (

$\left[\rm {C/Fe}\right] = -0.33 \pm 0.08$

) and otherwise 'normal'

$\left[\rm {X/Fe}\right]$

abundances, suggesting enrichment with Type II supernova that proceeds enrichment from massive asymptotic giant branch stars. This study reveals the substantial degree of chemical diversity in the stellar populations which assembled the early Milky Way.

A New Approach for Constraining Large-scale Temperature Fluctuations in the Intergalactic Medium

First Author: Etezad-Razavi, Saba
Instruments: XSHOOTER
ProgramIDs: 189.A-0424
BibCode: 2026ApJ...998..179E

The reionization of helium is thought to occur at 2.5 ≲ z ≲ 4, marking the last phase transition and final global heating event of the intergalactic medium (IGM). Since it is driven by rare quasars, helium reionization should give rise to strong temperature fluctuations in the IGM between neutral and recently ionized regions of order σ(lnT)∼∆T/T=20%−50% . We introduce a novel method to search for reionization-induced temperature fluctuations in the IGM, by using the effective optical depths of the Lyα forest toward a large number of background quasars. Higher IGM temperatures give rise to lower effective optical depths in the Lyα forest, implying that temperature fluctuations will broaden the observed optical depth distribution. We measure the distributions of the effective Lyα forest optical depths across 71 X-Shooter spectra from the XQ-100 survey in four redshift bins, from z = 3.76 to z = 4.19, and compare them to a large-volume cosmological hydrodynamical simulation. A good agreement is found between the observations and the simulation, which does not include temperature fluctuations; therefore, we do not detect a signature of helium reionization. We then postprocess the simulations to include an increasing amount of temperature fluctuations, until the model becomes inconsistent with the observations. We obtain tight constraints on σ(lnT)<0.29(<0.40) at 2σ (3σ) at z = 3.76 when averaging over a scale of 100 comoving Mpc, with weaker constraints for higher redshifts and smaller scales. Our constraints are the tightest to date, implying that either the IGM temperature contrast caused by helium reionization is less than ∼30% or the process has not yet significantly started at z = 3.76.

Introducing PxP: A Population Synthesis Framework for Predicting Young Stellar Object Properties

First Author: Peltonen, J.
Instruments: ALMA_Band_3
ProgramIDs: 2022.1.00276.S
BibCode: 2026ApJ..1001..170P

The most direct method of measuring the star formation rate is with young stellar objects (YSOs), but this requires high-resolution observations and high-quality models. Using the latest YSO radiation transfer and stellar evolution models, we have developed a population synthesis code that generates model YSO populations that can be observed by JWST. We combine these model populations with principal component analysis (PCA) and maximum likelihood fitting to create a complete framework for predicting the ages and masses of YSO populations. We dub this combination of population synthesis and PCA as PxP, and show that it is effective at predicting masses and ages with self-fitting tests. We apply PxP to Spitzer Space Telescope─identified YSOs in N44 and find a mass of (1.1 ± 0.1) × 10⁴ M_⊙ and an age of 0.74−0.03+0.06 Myr, consistent with previous work. Next, we identify 112 YSO candidates in the archival JWST observations of NGC 604. Applying PxP to this newly identified population we find a mass of (2.2 ± 0.2) × 10⁴ M_⊙ and an age of 0.62 ± 0.01 Myr. This first look at this framework demonstrates its effectiveness with a specific set of models and leaves clear opportunities for future exploration. PxP allows us to directly determine the recent (<3 Myr) star formation history, giving an unprecedented look at the effect of the large-scale environment on individual star formation.

Molecular gas and star formation in central rings across nearby galaxies

First Author: Gleis, Damian R.
Instruments: ALMA_Band_6, MUSE
ProgramIDs: 098.B-0551, 094.B-0321, 099.B-0242, 0100.B-0116, 1100.B-0651, 097.B-0640, 098.C-0484, 094.C-0623, 095.C-0473, 2013.1.01161.S, 2015.1.00121.S, 2015.1.00925.S, 2015.1.00956.S, 2016.1.00386.S, 2017.1.00392.S, 2017.1.00886.L, 2018.1.01651.S
BibCode: 2026A&A...707A.121G

Context. Nearby galaxies exhibit a variety of structures, including so-called central or (circum-)nuclear rings that are similar to the Milky Way (MW) Central Molecular Zone (CMZ). These rings are common in barred galaxies and can be gas-rich and highly star-forming. Aims. We aim to study the molecular gas content and star formation rate of central rings within nearby galaxies and link them to global galaxy properties, especially the bar morphology. Methods. We utilized 1″(≲100 pc) resolution CO(2─1) observations from the PHANGS-ALMA survey, visually identifying 20 central rings and determine their properties. For 14 of these rings, MUSE observations tracing star formation rate (SFR) surface density were available. We derived the rings' geometry, integrated molecular gas masses, SFRs, depletion times, and compared them to host galaxy and bar properties from the literature. Results. Molecular gas is an effective tracer for central rings. Previous studies have used ionized gas and dust tracers to identify central rings in galaxies of similar morphological types as the PHANGS galaxies (numerical Hubble type T ∼ −3 to T ∼ 9). In comparison, molecular gas yields similar fractions of galaxies hosting central rings and similar radii distributions. The gaseous central rings have typical radii of ∼ 400⁺²⁵⁰₋₁₅₀ ∼ 400 − 150 + 250 pc, molecular gas masses of log(M/M_⊙) ∼ 8.1^+0.17_−0.23 log ( M mol / M ⊙ ) ∼ 8 . 1 − 0.23 + 0.17 , and SFRs of ∼ 0.21^+0.15_−0.16 M_⊙/yr ∼ 0 . 21 − 0.16 + 0.15 M ⊙ / yr . As a result, they contribute 5.6^+4.5_−2.1% 5 . 6 − 2.1 + 4.5 % and 13⁺¹⁰₋₅% 13 − 5 + 10 % to their host galaxies' molecular gas mass and SFR, respectively. While the MW CMZ sits at the lower end of the radius, molecular gas mass, and SFR distribution, it matches well in terms of ring molecular gas mass and SFR fraction, and depletion time. Longer bars contain more massive molecular central rings, but there is no correlation between the classical bar strength parameters (Q_b, ∊_bar, A₂^max) and the ring's molecular gas content. Conclusions. Although absolute central ring properties (ring radius, molecular gas mass, SFR) likely depend on host galaxy properties, the similarities between the MW CMZ and PHANGS central rings in relative parameters (molecular gas and SFR fraction, depletion time) suggest that the processes of gas inflow and star formation are similar for central rings across nearby galaxies.

The Periastron Passage of T Tauri South B as Viewed by ALMA: Millimeter Flux Variations and Dust Heating Triggered by Orbital Motion

First Author: Beck, Tracy L.
Instruments: ALMA_Band_6, ALMA_Band_7
ProgramIDs: 2019.1.00703.S, 2022.1.01134.S
BibCode: 2026ApJ...999..122B

We present 225 and 350 GHz imaging of the iconic T Tauri system using the Atacama Large Millimeter submillimeter Array (ALMA). T Tauri is a hierarchical triple system, and the close binary T Tau Sa/Sb underwent periastron passage in 2023 March. The ALMA images were obtained in epochs spanning 2019 November through 2023 June, and therefore covered the time frame of the recent periastron passage. We clearly resolve the Sa─Sb binary in two epochs of high-resolution measurements with ALMA. We find increases in millimeter flux from heating of the Sa disk and the wider distribution of dust in the environment of the binary. This heating is likely in response to increased stellar accretion activity triggered by orbital motion during the dynamic periastron passage of T Tau Sb around Sa. Resolved, extended millimeter emission is also found to change morphology and increase in flux in the immediate environment of the Sa─Sb binary after periastron passage. This may suggest an increase in nonthermal emission from magnetic interaction, gravitational disruption of the circumstellar disks as the stars passed through periastron, or both of these phenomena. We also detected structures in the compact (24 au radius), thermal dust disk around T Tau N. In particular, we identify a crescent-shaped emission excess just outside a shallow gap at 12 au radius that appears to move at Keplerian speed. Future measurement of dust spectral indices can clarify the origin of increased and variable millimeter emission in the environment of the T Tau S binary.

A Close Quasar Pair in a Massive Galaxy Merger at z = 5.7

First Author: Yue, Minghao
Instruments: ALMA_Band_7
ProgramIDs: 2021.1.01052.S
BibCode: 2026ApJ..1002L..28Y

Close quasar pairs are rare products of galaxy mergers in which both supermassive black holes (SMBHs) are actively accreting, offering strong constraints on merger-driven active galactic nuclei evolution. Identifying close quasar pairs at z ≳ 4 is challenging due to the declining quasar number density in the early Universe. Here we report the confirmation of a close quasar pair at z = 5.7, J2037─4537, utilizing high-resolution Atacama Large Millimeter/submillimeter Array observations. The quasar host galaxies exhibit tidal disturbed features in both the far-infrared continuum emission and the [C II] line emission, ruling out the doubly imaged lensed quasar scenario. The two quasar hosts are massive (M_dyn ≳ 10¹⁰M_⊙) and star-forming (star formation rate ≳ 500M_⊙ yr⁻¹). The confirmation of J2037─4537 puts a lower limit on the quasar pair fraction at 5.5 < z < 6, F_pair > 1.2%, which is much higher than the quasar pair fraction at z ≲ 4. J2037─4537 is expected to form a gravitationally bound SMBH binary within ≲2 Gyr. The elevated quasar pair fraction at z > 5.5, as indicated by J2037─4537, likely contributes to the high gravitational-wave background reported by recent pulsar timing array experiments.

Multiphase Gas Structure in the Circumnuclear Region of NGC 5506 Observed with ALMA

First Author: Takechi, Kana
Instruments: ALMA_Band_7, ALMA_Band_8
ProgramIDs: 2017.1.00082.S, 2022.1.00410.S
BibCode: 2026ApJ..1002..100T

We present a study of the multiphase gas structure and kinematics of the circumnuclear disk (CND) of NGC 5506, a nearby edge-on Seyfert galaxy, at a spatial resolution of ∼20 pc. Observations of [C I](1─0), CO(3─2), and HCO⁺(4─3) obtained with the Atacama Large Millimeter/submillimeter Array reveal the CND dominated by rotational motion on scales of several hundred parsecs. No significant differences in geometrical thickness or velocity structure are found between [C I](1─0) and CO(3─2) across the CND, whereas HCO⁺(4─3) emission is more concentrated toward the disk plane. The ratio of velocity dispersion to rotational velocity, a proxy for disk scale height-to-radius ratio, is high (≳0.9) in the central region (≲30 pc) for both [C I](1─0) and CO(3─2), indicating geometrically thick structures in both tracers. Regions where the [C I](1─0)/CO(3─2) ratio exceeds the CND average are spatially correlated with the [O III]λ5007 bicone observed with the Hubble Space Telescope, suggesting that CO is preferentially dissociated by the AGN-driven biconical ionized outflow. The observed CND scale height and velocity dispersions traced by [C I](1─0) and CO(3─2) are consistent with a model in which supernova-driven turbulence provides the vertical support for the CND.

Hunting for methanol in the water-rich, planet-forming disk around HL Tau

First Author: Soave, A.
Instruments: ALMA_Band_7
ProgramIDs: 2017.1.01178.S, 2022.1.00905.S, 2015.1.00806.S, 2016.1.00629.S, 2016.1.00728.S, 2013.1.00100.S, 2012.1.00799.S, 2019.1.00393.S
BibCode: 2026A&A...708A.375S

Context. Methanol, the simplest complex organic molecule found in space, is considered a key compound for the formation of chemical species of prebiotic interest. Methanol detections in protoplanetary disks remain scarce, even though it is frequently detected in the material surrounding other young stellar objects (YSOs). Aims. We investigated the presence of methanol in the protoplanetary disk around the HL Tau protostar, motivated by the detection of spatially resolved warm water emission. Methods. Given the similar volatilities of methanol and water, thermally desorbed gas-phase methanol is expected to emit from the same region of the HL Tau disk where water vapor has been observed. Accordingly, we selected and imaged the most promising ALMA archival observations to search for rotational methanol lines. Results. We find no methanol emission in the analyzed archival datasets. Assuming optically thin emission and local thermodynamic equilibrium (LTE), we derive stringent upper limits on the methanol column density for different excitation temperatures: <7.2 × 10¹⁴ cm⁻² at 100 K and <1.8 × 10¹⁵ cm⁻² at 200 K, assuming a circular emitting region with a radius of 17 au (~0.12"). Furthermore, we obtain a stringent upper limit on the methanol-to-water column density ratio (<0.55 × 10⁻³ at 100 K and <1.4 × 10⁻³ at 200 K), which is, on average, an order of magnitude lower than the values measured for other YSOs and Solar System comets. Conclusions. We argue that the most likely explanation for the methanol nondetection in HL Tau is the presence of optically thick dust in the central region of the disk, which obscures part of the methanol emission. The upper limit on the methanol-to-water ratio in the HL Tau disk is at least an order of magnitude smaller than most clouds, YSOs, and comets, possibly due to radiative transfer and/or excitation effects, or to a different chemical evolution compared to the other sources.

IRAM 04191+1522: A compact proto-brown dwarf binary candidate

First Author: Huélamo, N.
Instruments: ALMA_Band_6, ALMA_Band_7
ProgramIDs: 2016.1.00039.S, 2016.1.01284.S, 2017.1.00551.S
BibCode: 2026A&A...709L...3H

Context. Very low luminosity objects (VeLLOs) in nearby star-forming regions have been identified as promising proto-brown dwarf candidates, and studying their multiplicity can shed light on the dominant formation mechanism of substellar objects. Aims. Our aim is to study the multiplicity of the VeLLO IRAM 04191+1522. Methods. We obtained 0.89 mm ALMA observations with a very extended configuration that achieved an angular resolution of ∼0 _.^″ . ″ 04 (6 au at 140 pc). We complemented these data with new VLA observations and ALMA archival data at 1.3 mm. Results. We resolved IRAM04191+1522 into a close binary candidate for the first time. The binary is detected in the ALMA continuum data with a projected separation of ∼80 mas (or 11 au at a distance of 140 pc). The two sources are oriented in the east-west direction, with the eastern component being brighter and more extended than the western one, which is marginally resolved. Analysis of C¹⁸O (2-1) archival data revealed gaseous material in rotation around the binary, presumably from a circumbinary disk with ∼27 au of radius centered on the faintest ALMA component. A fit of the position-velocity diagram allowed us to estimate a total dynamical mass for the system of 50 ± 40 M_Jup. Therefore, we classify IRAM04191 as a tight proto-brown dwarf binary candidate. The VLA data revealed the detection of a single object closer to the western ALMA source with a spectral index consistent with a radio jet. ★ Based on observations obtained at the ALMA Observatory under programs 2017.1.00551.S and 2016.1.00039.S.

Which is the most eccentric binary known? Insights from the 2023/4 pericenter passages of Zeta Boötis and Eta Ophiuchi

First Author: Waisberg, Idel
Instruments: GRAVITY
ProgramIDs: 111.24UP, 111.264P, 113.26HF
BibCode: 2025OJAp....8E..63W

There is a clear dearth of very eccentric binaries among those for which individual eccentricities can be measured. In this paper we report on observations of the two nearby, bright and very eccentric visual binaries Zeta Bo"otis ( ζ Boo) and Eta Ophiuchi ( η Oph), for which VLTI/GRAVITY interferometric observations were obtained during their pericenter passages in 2023/4. Previous observations of ζ Boo suggest an eccentricity e>0.99 with high significance, implying that it has the highest eccentricity of any known binary. However, our interferometric measurements near periastron passage reveal that the eccentricity is actually e=0.980450±0.000064 (second highest well constrained eccentricity) with a pericenter distance ap=0.818±0.009 au. We attribute the previous over-estimation to a degeneracy that plagues very eccentric visual binary orbital solutions. For η Oph we find an eccentricity e=0.93077±0.00013 (compared to previous estimates of e=0.95±0.02), a pericenter distance ap=2.15±0.10 au and attribute the over-estimated dynamical mass in the previous solution to an underestimated error in the semi-major axis. In both systems full circularization is expected as the stars evolve and expand, ultimately leading to close binaries with no memory of their very eccentric past.

Probing infrared eXcess to investigate early-Universe dust (PIXIEDust)

First Author: Bakx, Tom J. L. C.
Instruments: ALMA_Band_4, ALMA_Band_5, ALMA_Band_6, ALMA_Band_7, ALMA_Band_8
ProgramIDs: 2015.1.00428.S, 2016.1.00117.S, 2017.1.00225.S, 2017.1.00486.S, 2017.A.00026.S, 2018.1.00236.S, 2018.1.00295.S, 2018.1.00616.S, 2018.1.01241.S, 2019.1.00327.S, 2019.1.00343.S, 2019.1.00397.S, 2019.1.01350.S, 2019.1.01634.L, 2019.A.00015.S, 2021.1.00389.S, 2021.A.00020.S, 2021.A.00022.S, 2021.A.00023.S, 2022.1.01401.S, 2022.1.01562.S, 2023.1.00180.L, 2023.1.00336.S, 2023.A.00003.S, 2023.A.00017.S, 2023.A.00037.S, 2024.1.01645.S, 2024.1.01771.S, 2024.A.00007.S
BibCode: 2026MNRAS.546f2284B

Despite the implied presence of dust through reddened UV emission in high-redshift galaxies, no dust emission has been detected in the (sub)millimetre regime beyond

$z > 8.3$

. This study combines around 200 h of Atacama Large Millimetre/submillimetre Array (ALMA) and Northern Extended Millimetre Array (NOEMA) observations on 10

$z > 8$

galaxies, revealing no significant dust emission down to a

$1 \sigma$

depth of 2.0, 2.0, and

$1.5 \, \mu$

Jy at rest-frame 158, 88

$\mu$

m, and across all the data, respectively. This constrains average dust masses to be below

$< 10^{5}$

$_{\odot }$

$3 \sigma$

and dust-to-stellar mass ratios to be below

$3.7 \times {} 10^{-4}$

(assuming

$T_{\rm dust} = 50$

K and

$\beta _{\rm dust} = 2.0$

). Binning by redshift (

$8 < z < 9.5$

and

$9.5 < z < 15$

), UV-continuum slope (

$\beta _{\rm UV} \lessgtr -2$

), and stellar mass (

$\log _{10} M_{\ast }/{\rm {M}_{\odot }} \lessgtr 9$

) yields similarly stringent constraints. Combined with other studies, these results are consistent with inefficient dust build-up in the

$z > 8$

Universe, likely due to inefficient supernova production, limited interstellar grain growth and/or ejection by outflows. We provide data and tools online to facilitate community-wide high-redshift dust searches.

ALMA Lensing Cluster Survey: A Near-infrared-dark Submillimeter Galaxy at z > 4.5

First Author: Fang, Ji
Instruments: ALMA_Band_3, ALMA_Band_4, ALMA_Band_6
ProgramIDs: 2018.1.00035.L, 2021.1.00407.S
BibCode: 2026RAA....26e5002F

We present a study of a near-infrared-dark (NIR-dark) submillimeter galaxy R0600-C67, initially detected in the Atacama Large Millimeter/submillimeter Array (ALMA) Lensing Cluster Survey program. Due to the lack of robust emission lines from spectral line-scan observations at ALMA's 3 mm and 2 mm bands, we utilize two spectral energy distribution (SED) fitting codes, EAZY and CIGALE, to derive a robust photometric redshift of z = 4.7 ± 0.9, based on the observations from ALMA and James Webb Space Telescope (JWST), making it as a rare NIR-dark object at high redshift. Based on the SED analysis, we derive the physical properties of R0600-C67. Joint spatial imaging analyses suggest that stellar body traced by JWST, significantly larger than the compact dust continuum from ALMA. While we test for an active galactic nucleus (AGN), the current SED fitting analysis provides no conclusive evidence for its presence. Future mid-infrared observations would be essential to clarify the presence of an AGN.

ALMA Band 3 Source Counts: A Machine Learning Approach to Contamination Mitigation below 5 Sigma

First Author: Baronchelli, Ivano
Instruments: ALMA_Band_3
ProgramIDs: 2013.1.00376.S, 2013.1.00659.S, 2015.1.00030.S, 2015.1.00212.S, 2015.1.00702.S, 2015.1.00752.S, 2015.1.00979.S, 2015.1.01170.S, 2015.1.01246.S, 2016.1.00010.S, 2016.1.00324.L, 2016.1.00393.S, 2016.1.00406.S, 2016.1.00481.S, 2016.1.00543.S, 2016.1.00605.S, 2016.1.01155.S, 2017.1.00293.S, 2017.1.00300.S, 2017.1.00497.S, 2017.1.01223.S
BibCode: 2024Galax..12...26B

We performed differential number counts down to 4.25 sigma using ALMA Band 3 calibrator images, which are known for their high dynamic range and susceptibility to various types of contamination. Estimating the fraction of contaminants is an intricate process due to correlated non-Gaussian noise, and it is often compounded by the presence of false positives generated during the cleaning phase. In addition, calibrator extensions further complicate the counting of background sources. In order to address these challenges, our strategy employs a machine learning-based approach utilizing the UMLAUT algorithm. UMLAUT assigns a value to each detection, and it considers how likely it is for there to be a genuine background source or a contaminant. With respect to this goal, we provide UMLAUT with eight observational input parameters, each automatically weighted using a gradient descent method. Our methodology significantly improves the precision of differential number counts, thus surpassing conventional techniques, including visual inspection. This study contributes to a better understanding of radio sources, particularly in the challenging sub-5 sigma regime, within the complex context of a high dynamic range of ALMA calibrator images.

Exploring the effects of diffuse ionised gas in two local analogues of high-redshift star-forming galaxies

First Author: Lagos, P.
Instruments: MUSE
ProgramIDs: 0101.A-0282, 094.B-0745
BibCode: 2026A&A...706A..88L

Aims. We investigate the impact of diffuse ionised gas (DIG) on the determination of emission line ratios and gas-phase metallicities in two local analogues of high-redshift star-forming galaxies: UM 462 and IIZw 40. Understanding how DIG affects these quantities is essential for interpreting unresolved observations of distant galaxies, where integrated spectra are often used to trace their chemical evolution. Methods. Using archival Very Large Telescope, Multi-Unit Spectroscopic Explorer (MUSE) data, we spatially resolved the warm ionised medium of both galaxies. We derived oxygen abundances through the direct method and several HII-based strong-line calibrators, and we used the Hα surface brightness (Σ(Hα)) to distinguish regions dominated by HII or DIG emission. Results. Oxygen abundances derived from the N2 and O3N2 indices show an inverse correlation with Σ(Hα), ionisation parameters, and Hα equivalent width (EW(Hα)), with DIG-dominated regions exhibiting 12 + log(O/H) values higher than the mean for their galaxy by ∼0.2 dex in UM 462 and ∼0.1 dex in IIZw40. The metallicity differences derived from these strong-line calibrators reach about 0.4 dex and 0.3 dex between the highest (HII-dominated) and lowest (DIG-dominated) Σ(Hα) bins in UM 462 and IIZw40, respectively. We found a linear correlation between ∆(O/H) (O/H deviation from the mean interstellar medium value) and EW(Hα). Trends with Σ(Hα), metallicity, EW(Hα), and ionisation parameter suggest smoothly evolving ionisation conditions in the interstellar medium in our galaxies. Such trends and metallicty variations derived from HII-based calibrators reflect different ionisation sources and levels rather than true abundance changes. In particular, the use of these calibrators can lead to spurious metallicity gradients in galaxies with extended DIG tails, such as tadpole or cometary-like galaxies, which can be misinterpreted as evidence of the infall of metal-poor gas. The most likely mechanism for ionising the DIG in our sample of HII or BCD galaxies is the leakage of photons from HII regions, with shocks induced by stellar feedback processes also contributing significantly. Consequently, such contamination may affect the reliability of the derived oxygen abundances. Our results highlight the importance of accounting for DIG in galaxy metallicity estimates since it potentially biases metallicity gradient measurements. This is particularly relevant for large surveys at high redshift that rely on integrated galaxy spectra.

BASS. L. Near-infrared Data Release 3: A Spectral Atlas and Characterization of Active Galactic Nuclei

First Author: Gillette, Jarred
Instruments: XSHOOTER
ProgramIDs: 108.229H, 110.241X, 112.25LU, 099.A-0403, 0100.B-0672, 0101.A-0765, 0102.A-0433, 109.22YE, 106.21B1, 105.20DA, 0104.A-0353, 0103.A-0521, 098.A-0635
BibCode: 2026ApJS..282...68G

We present an analysis of near-infrared (NIR) emission-line properties, active galactic nucleus (AGN) diagnostics, and circumnuclear gas dynamics for 453 hard X-ray selected (14─195 keV) AGNs from the BAT AGN Spectroscopic Survey NIR Data Release 3 (DR3; = 0.036, z < 1.0). This dataset is the largest compilation of rest-frame NIR spectroscopic observations of hard-X-ray-selected AGNs and includes the full DR2 sample. Observations were obtained with the Very Large Telescope X-Shooter, a multiwavelength (0.3─2.5 μm) spectrograph (R = 4000─18,000), using a ≥ 2σ detection threshold, enabling broad analysis of emission features. We find that NIR coronal lines, particularly [Si VI] λ1.964, are more reliable tracers of AGN luminosity than optical OIII , showing a tighter correlation with hard X-ray luminosity (σ = 0.25 dex) than OIII λ5007 (σ = 0.55 dex). Broad Paschen lines (Paα and Paβ) are detected in 12% of Seyfert 2 and 57% of Seyfert 1.9 galaxies, consistent with previous hidden broad-line region (BLR) studies. We introduce a refined NIR diagnostic diagram ([Fe II] λ1.257 μm/Paβ and H₂ λ2.122 μm/Brγ) that effectively distinguishes AGN, star-forming, and composite sources even when contamination limits individual diagnostics or only upper limits are available. Additionally, we find a moderate correlation (p ≍ 7.4 × 10⁻³) between hot molecular gas mass (traced by H₂ 2.121 μm) and X-ray luminosity, while its relation with Eddington ratio is weaker. The hot-to-cold gas mass ratio spans 4 orders of magnitude, averaging ∼3 × 10⁻⁷, indicating diverse molecular gas excitation processes likely driven by star formation and AGN feedback. Our results underscore the value of NIR spectroscopy in probing AGN activity, obscured BLRs, and the complex interactions between AGNs and their circumnuclear environments.

SN 2024aecx: A Fast-evolving Type IIb Supernova with a Prominent Shock-cooling Peak

First Author: Xi, Qiang
Instruments: MUSE
ProgramIDs: 099.B-0242, 098.B-0551
BibCode: 2026ApJ...998...98X

SN 2024aecx is a nearby (∼11 Mpc) Type IIb SN discovered within ∼1 day after explosion. In this paper we report high-cadence photometric (typically 0.5 ∼ 1 day) and spectroscopic follow-up observations, conducted from as early as 0.27 day post discovery out to the nebular phase at 158.4 days. We analyze the environment of SN 2024aecx and derive a new distance (11.3 ± 1.1 Mpc), metallicity and host extinction. The light curve exhibits a hot and luminous shock-cooling peak at the first few days, followed by a main peak with very rapid postmaximum decline. The earliest spectra are blue and featureless, while from 2.3 days after discovery prominent P-Cygni profiles emerge. At nebular phase, the emission lines exhibit asymmetric and double-peaked profiles, indicating asphericity and/or early dust formation in the ejecta. Nebular spectral modelling indicates a blueshifted O-rich clump moving toward observer, and the [O I]/[Ca II] line ratio suggests an intermediate-mass progenitor. We simulated the progenitor and explosion using a two-component model of shock cooling and radioactive ⁵⁶Ni heating; our model favors an extended, low-mass H-rich envelope with M_e = 0.04 ± 0.01 M_⊙ and a low ejecta mass of Mej=1.55−0.14+0.18M⊙ . And the nebular-phase spectra and light-curve modelling both suggest that it most likely originated from an intermediate-mass binary progenitor system. The comprehensive monitoring of SN 2024aecx, coupled with the detailed characterization of its local environment, establishes it as a benchmark event for probing the progenitors and explosion mechanisms of Type IIb SNe.

Juno radio occultations reveal the structure of Jupiter's cold northern polar vortex

First Author: Smirnova, Maria
Instruments: VISIR
ProgramIDs: 114.277Q
BibCode: 2026A&A...706A.109S

Context. Jupiter's polar upper troposphere and stratosphere host a persistent cold vortex poleward of 65°N, but its detailed structure and dynamics have remained difficult to resolve. Aims. The goal is to characterize the thermal structure and dynamics of the polar vortex using new and complementary remote sensing techniques. Methods. We used a combination of high-resolution vertical profiles derived from Juno's recent radio occultation measurements and mid-infrared imaging from the VLT/VISIR instrument. The former provided direct retrievals of temperature and density near and within the vortex, while VISIR imaging revealed spatial thermal contrasts across the region. Results. Our analysis confirms the presence of a steep meridional temperature jump at 65°N, of about 7±1 K at 100 mbar, which is consistent with a strong vertical wind shear and a prograde polar stratospheric jet reaching up to 80 ms⁻¹ at the 10 mbar level. We find the atmosphere to be thermally stable above 0.55 bar, reaching a Brunt-Väisälä frequency of 0.025 s⁻¹ in the mid-stratosphere. Thermal contrasts observed in the infrared data align with the vertical structures inferred from radio occultations, which validates the presence and extent of the cold vortex. Conclusions. These findings offer a quantitative analysis of the thermal structure and the dynamical behavior of Jupiter's polar atmosphere and demonstrate the diagnostic power of combining radio occultation and thermal infrared techniques in planetary atmospheric studies.

MUSE Study of Two Giant Low-surface-brightness Galaxies with Compact Satellites

First Author: Saburova, Anna S.
Instruments: MUSE
ProgramIDs: 110.24DN
BibCode: 2026ApJ...998...19S

Giant low-surface-brightness galaxies (gLSBGs) are rare objects with disk radii up to 160 kpc and dynamical masses of up to the order of 10¹² M_⊙. Their very existence challenges currently accepted theories of galaxy formation and evolution, as it is difficult to build such large, dynamically cold disks through mergers without destroying them. We present deep MUSE mosaic observations of two nearby gLSBGs with compact elliptical satellites: UGC 1382, which hosts a globally counterrotating gaseous disk, and AGC 192040, which does not. We analyze properties of ionized gas and present spatially resolved maps of kinematics and metallicity, as well as stellar population analysis for the central regions of the galaxies. The radial gradients of gas-phase metallicities are flat for both galaxies. Our observational data indicate that both galaxies experienced mergers several Gyr ago. However, the scenarios of the formation of giant disks appear to be slightly different for these two systems. For AGC 192040, we propose gas accretion from the filament or from the cooling hot halo gas followed by a merger with a companion on a prograde orbit at an intermediate mass ratio. For UGC 1382, multiple gas-rich mergers with companions on retrograde orbits are preferred by the data.

Ancient Relic Moderately Metal-rich Bulge Cluster Tonantzintla 2

First Author: Ortolani, Sergio
Instruments: FORS2
ProgramIDs: 113.26MS
BibCode: 2026ApJ...998L...8O

The assembly history of the Galactic bulge is intimately tied to the formation of the proto─Milky Way, yet reconstructing this early phase is difficult because mergers and secular evolution have erased most of its original structure. Among present-day stellar systems, only globular clusters retain the ancient signatures needed to trace these primordial building blocks. Here we present the most detailed characterization to date of Tonantzintla 2, a prime candidate for a relic of the Milky Way's primordial bulge. It is a moderately metal-rich globular cluster projected onto the bulge that has remained largely unexplored despite its potential to constrain the early formation of the inner Milky Way. We derive its fundamental parameters using proper-motion-corrected Hubble Space Telescope WFC3 and Advanced Camera for Surveys photometry. By applying an isochrone fitting to very clean data, we obtain an age of 13.58 −1.0+0.72 Gyr, a reddening E(B ─ V) = 1.44 ± 0.02, a metallicity [M/H] = −0.68 −0.05+0.04 , and a heliocentric distance of d_⊙ = 7.38 0.080.13 kpc. A complementary chemical-abundance analysis of seven member stars from APOGEE high-resolution spectroscopy reveals an enrichment pattern consistent with an in situ origin. Tonantzintla 2 is among the oldest globular clusters studied in the literature, and the oldest so far analyzed in the Galactic bulge. Its age places a stringent constraint on the onset of the bulge formation, implying that star formation in the inner Galaxy began within ∼0.2 Gyr of the Big Bang and that Tonantzintla 2 represents an exceptional relic of the Milky Way's earliest chemical enrichment.

Pre-perihelion evolution of the NiI/FeI abundance ratio in the coma of the interstellar comet 3I/ATLAS: From extreme to normal

First Author: Hutsemékers, Damien
Instruments: UVES, XSHOOTER
ProgramIDs: 115.29F3, 115.27ZL, 115.27ZJ
BibCode: 2026A&A...706A..43H

Emission lines of FeI and NiI are commonly found in the coma of Solar System comets, even at large heliocentric distances. These atoms are most likely released from the surface of the comet's nucleus or from a short-lived parent. The presence of these lines in cometary spectra is unexpected because the surface blackbody equilibrium temperature is too low to allow the sublimation of refractory minerals containing these metals. These lines were also found in the interstellar comet 2I/Borisov, which has a NiI/FeI abundance ratio similar to that observed in Solar System comets. On average, this ratio is one order of magnitude higher than the solar Ni/Fe abundance ratio. Here, we report observations of the interstellar comet 3I/ATLAS, which were carried out with the ESO Very Large Telescope equipped with the UVES and X-shooter spectrographs. Spectra were obtained at heliocentric distances ranging from 3.14 to 1.85 au. Nil was detected at all epochs. FeI was only detected at heliocentric distances smaller than 2.64 au. We estimated the Nil and FeI production rates by comparing the observed line intensities with those produced by a dedicated fluorescence model. Comet 3I first exhibited extreme and unusual NiI/FeI abundance ratios during the initial stages of its activity. However, as its heliocentric distance decreased, this ratio became indistinguishable from those observed in Solar System comets and in comet 2I∕Borisov. Comet 3I was found to be C₂-depleted, with a NiI/FeI abundance ratio finally consistent with other C₂-depleted comets. Nevertheless, comet 3I remains exceptional due to its high, total production rate of NiI and FeI, which is at least one order of magnitude larger than that of other comets. We interpreted these observations assuming that the NiI and FeI atoms were released through the sublimation of Ni(CO)₄ and Fe(CO)₅ carbonyls. This scenario provides a straightforward explanation for the asymmetric release of NiI and FeI atoms in the cometary coma and how it depends on the heliocentric distance. It also supports the presence of carbonyls in the cometary material.

Mass estimates of the young TOI-451 transiting planets: multidimensional Gaussian Process on stellar spectroscopic and photometric signals

First Author: Barragán, Oscar
Instruments: ESPRESSO
ProgramIDs: 112.25HY, 112.261J
BibCode: 2026MNRAS.546ag087B

The young TOI-451 planetary system, aged 125 Myr, provides a unique opportunity to test theories of planetary internal structures and atmospheric mass-loss through examination of its three transiting planets. We present an exhaustive photometric and spectroscopic follow-up to determine the orbital and physical properties of the system. We perform multidimensional Gaussian Process regression with the code pyaneti on spectroscopic time-series and NGTS/LCO light curves to disentangle the stellar and planetary signal in ESPRESSO radial velocities. We show how contemporaneous photometry serves as an activity indicator to inform RV modelling within a multidimensional Gaussian Processes framework. We argue that this can be exploited when spectroscopic observations are adversely affected by low signal-to-noise and/or poor sampling. We estimate the Doppler semi-amplitudes of

$k_{\rm b}=$

$2.6_{-1.2}^{+1.1}$

$\mathrm{m\, s^{-1}}$

$k_{\rm c}=$

$1.2_{-0.8}^{+1.0}$

$\mathrm{m\, s^{-1}}$

, and

$k_{\rm d}=$

$2.7 \pm 1.2$

$\mathrm{m\, s^{-1}}$

. This translates in 2

$\sigma$

mass estimates for TOI-451 b and d of

$M_{\rm b}=$

$4.7_{-2.2}^{+2.1}$

$\mathrm{M_{\rm{\oplus }}}$

and

$M_{\rm d}=$

$10.2_{-4.5}^{+4.6}$

$\mathrm{M_{\rm{\oplus }}}$

; as well as a mass upper limit for TOI-451 c of

$M_{\rm c} \lt 11.5\, M_{\rm{\oplus }}$

. The derived planetary properties suggest that planets c and d contain significant hydrogen-rich envelopes. The inferred parameters of TOI-451 b are consistent with either a rocky world that still retains a small hydrogen envelope or a water world. These insights make the TOI-451 system an ideal laboratory for future follow-up studies aimed at measuring atmospheric compositions, detecting atmospheric mass-loss signatures, and further exploring planetary formation and evolution processes.

A Morphokinematic Study of Galactic High-abundance Discrepancy Factor Planetary Nebulae Based on the VLT/UVES Deep Spectroscopy

First Author: Huang, Haomiao
Instruments: UVES
ProgramIDs: 69.D-0174, DataDoiProID
BibCode: 2026ApJS..282...63H

We report detailed analyses of deep, high-resolution spectra of three Galactic planetary nebulae (PNe) with high abundance discrepancy factors (ADFs), Hf 2-2, M 1-42, and NGC 6153, obtained with the Ultraviolet and Visual Echelle Spectrograph on the 8.2 m Very Large Telescope. These spectra were carefully reduced, including rigorous absolute flux calibration, yielding a detection of ∼410─800 emission lines in each PN. Plasma diagnostics and abundance calculations were performed using nebular lines. In all three PNe, the electron temperatures derived using the collisionally excited lines (CELs) are higher than that yielded by the H I Balmer and Paschen jumps, while the temperatures yielded by the O II and N II optical recombination lines (ORLs) are very low, ≲2000 K, indicating that the heavy-element ORLs probe cold nebular regions. The ORL abundances of N, O, and Ne are systematically higher than the corresponding CEL values, confirming high ADFs in the three objects. Position─velocity diagrams were created, and spatiokinematical studies show that CELs come from the outer nebular regions, while the ORL-emitting regions are close to the nebular center. Additionally, the velocity indicated by CEL line-splitting decreases with ionization potential, which was not obvious in ORLs. These spatial and kinematic differences support two distinct components of ionized gas: a cold, metal-rich component and a warmer component with normal metallicity. Heavy elements are strongly enriched in the cold gas, while its H⁺ fraction is low but still produces significant H I emission, affecting CEL abundance estimates. *Based on the observations obtained with the Very Large Telescope (VLT) through program ID #69.D-0174A.

Characterizing the Low-mass Pre-main-sequence Population in the Low-metallicity Star-forming Region Dolidze 25 Using VLT-MUSE

First Author: Ashraf, Mizna
Instruments: FLAMES, GIRAFFE, MUSE, UVES
ProgramIDs: 384.B-0066, 082.D-0839, 098.C-0435
BibCode: 2026ApJ...998..116A

The metallicity of the star-forming environment is a fundamental parameter shaping the evolution of protoplanetary disks and the formation of planetary systems, yet its influence remains poorly constrained. We present a spectroscopic study of low-mass pre-main-sequence (PMS) stars (M < 1 M_⊙) in the exceptionally metal-poor cluster Dolidze 25 (Z ≍ 0.2 Z_⊙), using Very Large Telescope/MUSE observations to probe accretion processes and disk evolution in a subsolar environment. We identify 132 cluster members using a combination of Gaia astrometry and spectroscopic youth indicators, including lithium absorption and Balmer emission. The stellar parameters are derived using low-metallicity BT-Settl models yielding effective temperatures, extinctions, and luminosities enabling robust estimates of stellar masses and ages. Mass accretion rates ( Ṁacc ) derived from Hα emission span 10⁻¹⁰─10⁻⁸ M_⊙ yr⁻¹ with a median value of 8 × 10⁻¹⁰ M_⊙ yr⁻¹. These rates are comparable to those in solar-metallicity regions of a similar age, such as Lupus and Orion, indicating minimal metallicity dependence in accretion processes. Our analysis shows that using solar-metallicity templates to fit low-metallicity stars leads to systematic overestimations of T_eff (by approximately 300 K) and A_V (by around 0.5 mag), underscoring the importance of employing metallicity-matched models for reliable characterization in low-Z environments. We present flux-calibrated, extinction-corrected spectra of these metal-poor PMS stars as a valuable resource for future investigations of disk evolution in subsolar regimes.

ExoplaNeT accRetion mOnitoring sPectroscopic surveY (ENTROPY): II. Time series of Balmer line profiles of Delorme 1(AB)b

First Author: Demars, Dorian
Instruments: UVES
ProgramIDs: 108.21ZE, 110.23VU
BibCode: 2026A&A...706A..57D

Context. Accretion processes in the planetary-mass regime are still poorly constrained, yet they strongly impact the formation and evolution of planets and the composition of circumplanetary disks. Aims. We investigate the resolved Balmer hydrogen emission-line profiles and their variability timescales in the ∼13 M_Jup, 30−45 Myr-old companion Delorme 1 (AB)b to derive constraints on the accretion mechanism at play. Methods. With VLT/UVES, we collected 31 new epochs of high-resolution optical (330─680 nm) spectra of the companion at R = 50 000, probing variability on timescales of hours to years. We study the companion's H I emission line shape and flux variability and compare them to two proposed line origins: magnetospheric accretion funnel and localized accretion shock. Results. We detect H I Balmer lines from Hα up to H10 (6564─3799 Å), as well as the UV continuum excess ─ signs of ongoing accretion. All lines and UV excess are variable. The H I lines can be decomposed into two static components that vary only by their flux. The broader component in velocity correlates strongly with the UV excess, and its profile is qualitatively reproduced by magnetospheric accretion funnel models but clearly not by shock models. With strong relative variability, this broad component almost entirely explains the variability in the shape of the line profiles. The second, narrower component correlates less with the UV excess and is best reproduced by shock-emission models. Its strong absolute variability makes it responsible for most of the line flux variability. Overall, the lines have low relative flux variability on hourly timescales, but up to ∼100% on weekly timescales and beyond, a behavior similar to T Tauri stars. Conclusions. The properties of the broad component of the H I lines strongly support magnetospheric accretion. The narrow component could be due to an accretion shock as well as chromospheric activity. Higher-cadence observations could search for rotational modulations to constrain the object's rotational period and the exact geometry of the accretion flow.

Discovery of 13 new symbiotic stars in Gaia DR3

First Author: Akras, Stavros
Instruments: OMEGACAM
ProgramIDs: 177.D-3023
BibCode: 2026MNRAS.546ag105A

Symbiotic stars (SySts) are considered potential progenitors of Type Ia supernovae (SNe Ia). However, theoretical studies suggest that their contribution to the total number of SNe Ia rate is very small. The number of known SySts remains significantly lower, by orders of magnitude, than predicted by theory. Continued searches for new members are therefore essential to better constrain population synthesis models. In this study, we conduct a search for new potential SySts captured in Gaia's observations. Optical photometric data from IPHAS and VPHAS+, infrared data from 2MASS and WISE, and ultraviolet data from GALEX are combined to uncover hidden members in the Gaia catalogue of 12.4 million variable sources. For sources lacking optical data, synthetic optical data are computed using the low-resolution Gaia BP/RP spectra in order to identify the H

$\alpha$

emitters. By applying infrared and optical selection criteria, we identified 43 S-type and 11 D-type SySts that meet these requirements. Of these, 10 S-type and 3 D-type are considered highly probable candidates, while the remainder are already known members. Analysis of the Gaia BP/RP spectroscopic data confirms the presence of the H

$\alpha$

emission line as well as molecular bands in all 13 systems, validating their classification as bona fide SySts. Systematic searches for SySts and other rare stellar groups, integrating data from multiple publicly available catalogues, are essential to uncover previously hidden members.

Dark Energy Survey Year 6 Results: Photometric Dataset for Cosmology

First Author: Bechtol, K.
Instruments: VIRCAM
ProgramIDs: 179.A-2010
BibCode: 2026ApJS..282...62B

We describe the photometric dataset assembled from the full 6 yr of observations by the Dark Energy Survey (DES) in support of static-sky cosmology analyses. DES Y6 Gold is a curated dataset derived from DES Data Release 2 (DR2) that incorporates improved measurement, photometric calibration, object classification and value-added information. Y6 Gold comprises nearly 5000 deg² of grizY imaging in the south Galactic cap and includes 669 million objects with a depth of i_AB ∼ 23.4 mag at a signal-to-noise ratio ∼ 10 for extended objects and a top-of-the-atmosphere photometric uniformity <2 mmag. Y6 Gold augments DES DR2 with simultaneous fits to multiepoch photometry for more robust galaxy shapes, colors, and photometric redshift estimates. Y6 Gold features improved morphological star─galaxy classification with an efficiency of 98.6% and a contamination of 0.8% for galaxies with 17.5 < i_AB < 22.5. Additionally, it includes per-object quality information, and accompanying maps of the footprint coverage, masked regions, imaging depth, survey conditions, and astrophysical foregrounds that are used for cosmology analyses. After quality selections, benchmark samples contain 448 million galaxies and 120 million stars. This publication is complemented by data access and documentation.

The PHANGS-MUSE/HST-Hα nebulae catalogue: Parsec-scale resolved structure, physical conditions, and stellar associations across nearby galaxies

First Author: Barnes, A. T.
Instruments: MUSE
ProgramIDs: 094.C-0623, 095.C-0473, 098.B-0551, 097.B-0640, 0100.B-0116, 098.C-0484, 1100.B-0651, 094.B-0321, 099.B-0242
BibCode: 2026A&A...706A..95B

We present the PHANGS-MUSE/HST-Hα nebulae catalogue, comprising 5177 spatially resolved nebulae across 19 nearby star-forming galaxies (D < 20 Mpc), based on high-resolution Hα imaging from HST, homogenised to a fixed (10 pc) physical resolution and sensitivity. Combined with MUSE integral field spectroscopy, this enables robust classification of 4882 H II regions and the separation of planetary nebulae and supernova remnants. We derive electron densities for 2544 H II regions using [S II] diagnostics and adopt direct or representative electron temperatures for consistent physical characterisation. Nebular sizes are measured using circularised radii and intensity-weighted second moments, yielding a median radius of approximately 20 pc and extending down to (sub-)parsec (deconvolved) radii. A structural complexity score is introduced via hierarchical segmentation to trace substructure, highlighting that around a third of the regions are H II complexes containing several individual clusters and bubbles, with an increased fraction of these regions in galactic centres. A luminosity─size relation, calibrated using the resolved HST sample, is applied to 30 790 MUSE nebulae, allowing the recovery of nebular sizes down to ~1 pc and providing statistical completeness beyond the HST detection limit. Comparisons with classical Strömgren radii indicate that observed sizes are systematically larger, corresponding to typical volume filling factors with a median of ϵ ~ 0.22 (10th─90th percentile 0.06─0.78), with larger regions exhibiting progressively lower values. We associate 3349 H II regions with stellar populations from the PHANGS-HST association catalogue, finding median ages of ~3 Myr and typical stellar masses of around 10⁴─10⁵ M_⊙, supporting the link between ionised nebular and young stellar populations. We also assess the impact of diffuse ionised gas on emission-line diagnostics and after removing confirmed supernova remnants, find no strong variation in line ratios with nebular resolution, indicating minimal systematic bias in the MUSE catalogue. This dataset establishes a detailed, spatially resolved connection between nebular structure and ionising sources, and provides a benchmark for future studies of feedback, DIG contributions, and star formation regulation in the ISM, especially in combination with matched high-resolution observations. The full catalogue is made publicly available in machine-readable format.

A comprehensive study of δ Scuti-type pulsators in eclipsing binaries: Oscillating eclipsing Algols

First Author: Pawar, T.
Instruments: FEROS
ProgramIDs: 088.D-0080, 089.D-0097, 090.D-0061, 091.D-0145
BibCode: 2026A&A...705A.251P

Eclipsing double-lined spectroscopic binaries (SB2s) hosting δ Scuti-type pulsators offer a unique laboratory for simultaneously constraining stellar geometry and interior structure. In this study, we present a comprehensive analysis of five oscillating eclipsing Algol (oEA) binaries. By combining high-precision, short-cadence TESS photometry with multi-epoch high-resolution spectroscopy, we were able to derive precise stellar and orbital parameters. The frequency power spectra were obtained using residuals from binary modelling. We further investigated the evolutionary history of these systems using a grid of MESA binary evolution simulations. Our analysis suggests that the systems must have undergone either case A or case B mass transfer, with the primary components repositioned in the Hertzsprung─Russell (HR) diagram and now pulsating in the δ Scuti regime, while the cooler secondaries are underluminous and inflated, filling their Roche lobes. This study contributes to the growing catalog of well-characterised oEA systems and our understanding of the effects of mass-transfer on the fate of these short-period binaries.

Intertwined Birth and Death: A Herbig─Haro Outflow Resolves the Distance to Vela Junior

First Author: Suherli, Janette
Instruments: MUSE
ProgramIDs: 0104.D-0092
BibCode: 2026ApJ...997L..36S

The distance to the Vela Junior supernova remnant (RX J0852.0─4622 or G266.2─1.2) has long remained uncertain, limiting our understanding of its physical properties. Using Very Large Telescope/Multi Unit Spectroscopic Explorer integral field spectroscopy, we uncover chemical and kinematic connections between the nebula surrounding its central compact object (CXOU J085201.4─461753) and the nearby Herbig─Haro outflow of Ve 7─27 (Wray 16─30), indicating a shared nitrogen-rich, Fe-peak-enhanced environment. This link ties stellar birth and death, with the young star Ve 7─27 embedded in material expelled by Vela Junior's massive progenitor, and the remnant's blast wave is expanding through the same medium. Adopting the Gaia-based distance to Ve 7─27, we revise Vela Junior's distance to 1.41 ± 0.14 kpc. At this distance, the remnant's physical radius is 23.3 ± 2.3 pc, and X-ray proper motions of the northwestern rim correspond to shock speeds of (2.8 ± 0.7) × 10³ to (5.6 ± 1.5) × 10³ km s⁻¹. These imply an age of ∼1.6─3.3 kyr and a very low ambient density, indicating that Vela Junior is expanding within a highly rarefied wind-blown cavity carved by a massive progenitor—consistent with the nondetection of strong thermal X-ray emission. This distance update also resolves long-standing inconsistencies, with major implications for its energy budget, particle acceleration efficiency, and compact object evolution.

The RoPES project with HARPS and HARPS-N: II. A third planet in the multi-planet system HD 176986

First Author: Nari, N.
Instruments: HARPS
ProgramIDs: 109.2392, 112.25SF, 192.C-0852, 198.C-0836, 106.21TJ, 183.C-0972, 091.C-0936, 072.C-0488, 110.242T, 113.26U2, 114.27J9, 108.22CE
BibCode: 2026A&A...705A.252N

Context. Earth-like planets orbiting in the habitable zone of K- to G-type stars create an RV effect in amplitude of less than 1 ms⁻¹ and have orbital periods of hundreds of days. Only long-term RV surveys with sub-meter per second precision instruments can explore the outer regions of Sun-like stars and look for Earth-like planets and super-Earths. Detecting Earth-like or super-Earth planets in the habitable zone of Sun-like stars is crucial to provide targets to the next generation of direct imaging facilities. Aims. We present the analysis of the K-type star HD 176986. It has a brightness of V=8.45 mag and a distance from the Sun of d = 27.88 pc. This star hosts a known planetary system of two super-Earths. We utilize historical and recently collected RV measurements to investigate the presence of Earth- and super-Earth-like planets in the habitable zone of HD 176986. Methods. We monitored the system with HARPS and HARPS-N. We joined historical datasets with new data collected in an ongoing blind search program. We took advantage of recently developed tools for RV extraction and stellar activity filtering. The analysis of activity indicators permits us to determine the period of the magnetic cycle of the star alongside its rotation period. We performed a joint analysis of RVs and activity indicators through multidimensional GPs to better constrain the activity model in RVs and avoid overfitting. Results. We detected a new planet orbiting the star and retrieved the two known planets. HD 176986 b has an orbital period of 6.49164_−0.00029^+0.00030 d and a minimum mass of 5.36 ± 0.44 M⊕. HD 176986 c has an orbital period of P_c = 16.8124 ± 0.0015 d and a minimum mass of 9.75_−0.64^+0.65 M⊕. HD 176986 d has an orbital period of 61.376_−0.049^+0.051 d and a minimum mass of 6.76_−0.92^+0.91 M⊕. From the analysis of activity indicators, we find evidence of a magnetic cycle with a period of 2432₋₅₉⁺⁶⁴ d, along with a rotation period of 36.05_−0.71^+0.67 d. Conclusions. We discover a new planet in the multi-planet system orbiting the K-type star HD 176986. All the planets have minimum masses compatible with super-Earths or mini-Neptunes.

Sibling sub-Neptunes around sibling M dwarfs: TOI-521 and TOI-912

First Author: Lacedelli, G.
Instruments: ESPRESSO, HARPS
ProgramIDs: 113.26NP, 111.24PJ, 1102.C-0339, 112.25F2
BibCode: 2026A&A...705A.260L

Context. Sub-Neptunes are absent in the Solar System, yet they are the most common category of planets found in our Galaxy. This kind of planet challenges the internal structure models, prompts investigations into its formation and evolution, and pushes atmospheric characterisation studies to break the degeneracy in their inner composition. Aims. We report here the discovery and characterisation of new sub-Neptunes orbiting two similar M dwarfs, TOI-521 (T_eff = 3544 ± 100 K, V = 14.7 mag) and TOI-912 (T_eff = 3572 ± 100 K, V = 12.7 mag). Each star hosts a transiting planetary candidate identified by TESS and is part of the THIRSTEE follow-up programme, which aims to understand the sub-Neptune population through in-depth and precise characterisation studies on a population level. Methods. We analysed TESS light curves, ground-based photometry, and high-precision ESPRESSO, HARPS, and IRD radial velocities to confirm the planetary nature of both candidates, infer the precise orbital and physical parameters of the planets, and investigate the presence of additional planets in the systems. Results. The two stars host nearly identical planets in terms of mass and radius. TOI-521 hosts a transiting sub-Neptune in a 1.5-day orbit with radius and mass of R_b = 1.98 ± 0.14 R_⊕ and M_b = 5.3 ± 1.0 M_⊕, respectively. Moreover, we identified an additional candidate at 20.3 days, with a minimum mass of M_p sin i = 10.7_−2.4^+2.5 M_⊕, currently not detected as transiting in our photometric dataset. Similarly, the planet orbiting TOI-912 is a 4.7-d sub-Neptune with R_b = 1.93 ± 0.13 R_⊕ and M_b = 5.1 ± 0.5 M_⊕. Interestingly, TOI-912 b likely possesses an unusually high eccentricity (e = 0.58 ± 0.02) and is probably undergoing strong tidal dissipation. If such eccentricity were confirmed, it would make TOI-912 b one of the most eccentric sub-Neptunes known to date. TOI-521 b and TOI-912 b have very similar densities (~4 g cm⁻³), and they lie in the degenerate region of the mass-radius diagram where different compositions are plausible, including a volatile-rich composition, or a rocky core surrounded by a H-He envelope. When compared to the other THIRSTEE M-dwarf targets, our sample supports the division of sub-Neptunes into two distinct populations divided by a density gap. Both planets are interesting targets for atmospheric follow-up in the context of understanding the temperature-atmospheric feature trend that starts to emerge thanks to JWST observations.

EIGER. VII. The Evolving Relationship between Galaxies and the Intergalactic Medium in the Final Stages of Reionization

First Author: Kashino, Daichi
Instruments: XSHOOTER
ProgramIDs: 286.A-5025, 089.A-0814, 086.A-0574, 087.A-0607, 086.A-0162, 084.A-0360, 084.A-0390, 093.A-0707, 098.B-0537
BibCode: 2026ApJ...997..280K

We present a comprehensive analysis of the relationship between galaxies and the intergalactic medium (IGM) during the late stages of cosmic reionization, based on the complete JWST EIGER dataset. Using deep NIRCam 3.5 μm slitless spectroscopy, we construct a sample of 948 [O III]λ5008-emitting galaxies with −21.4 ≲ M_UV ≲ −17.2 spanning 5.33 < z < 6.97 along six quasar sight lines. We correlate these galaxies with Lyα and Lyβ transmission measured from high-resolution quasar spectra across multiple redshift intervals. We find clear redshift evolution in the correlation between galaxy density and transmission: it is suppressed in overdense regions at z < 5.50, while enhanced at 5.70 < z < 6.15. The intermediate range exhibits a transitional behavior. Cross-correlation measurements further reveal excess absorption within ∼8 cMpc of galaxies at low redshifts, and enhanced transmission at intermediate scales (∼5─20 cMpc) at z > 5.70. Statistical tests using mock catalogs with realistic galaxy clustering but no correlation with the transmission field confirm that the observed correlations are unlikely to arise by chance. The evolving signals can be explained by stronger absorption in overdense regions, combined with the competing influences of local radiation fields and the rising background radiation. While local radiation dominates ionization of the surrounding IGM at earlier times, the background becomes increasingly important, eventually surpassing the impact of nearby galaxies. These results support an inside-out progression of reionization, with ionized regions originating around clustered, star-forming galaxies and gradually extending into underdense regions.

The massive hot subdwarf binary LAMOST J065816.72+094343.1

First Author: Mattig, F.
Instruments: UVES
ProgramIDs: 114.28KP
BibCode: 2026A&A...706L...2M

Context. Massive short-period binaries involving hot subdwarf stars (sdO/Bs) are rare but very relevant to constraining pathways for binary star evolution. Moreover, some of the most promising candidate progenitor systems leading to Type Ia supernovae (SNe Ia) involve sdO/Bs. LAMOST J065816.72+094343.1 has been identified to be such a candidate system. Aims. To explore the nature and evolutionary future of LAMOST J065816.72+094343.1, we complemented archival spectroscopic data with additional time series spectra as well as high-resolution spectroscopy of the object. After combining these with photometric data, we determined the orbital parameters of the system and the mass of the companion. Methods. We solved the orbit of the system by analyzing 68 low- and medium-resolution spectra using state-of-the-art mixed local thermodynamic equilibrium (LTE) and non-LTE model atmospheres. Additionally, we gathered nine high-resolution spectra to determine atmospheric parameters and the projected rotational velocity of the sdOB. The inclination angle of the system was constrained assuming tidal synchronization of the sdOB, which was verified via analysis of the ellipsoidal variations in the TESS light curve. Results. We determine LAMOST J065816.72+094343.1 to be a binary consisting of a massive 0.82 ± 0.17 M_⊙ sdOB component with a 1.30^+0.31_−0.26 M_⊙ 1 . 30 − 0.26 + 0.31 M ⊙ unseen companion. Due to the companion's mass being very close to the Chandrasekhar mass limit and high for a white dwarf, it is unclear whether the compact companion is a white dwarf or a neutron star. We find the system to be in a close orbit, with a period of P = 0.31955193 d and an inclination angle of i = 49.6^+5.2_−4.2 deg i = 49 . 6 − 4.2 + 5.2 deg . While the exact nature of the companion remains unknown, we determine the system to either lead to a SN Ia or an intermediate mass binary pulsar, potentially after a phase as an intermediate-mass X-ray binary.

A Cool Earth-sized Planet Candidate Transiting a Tenth Magnitude K-dwarf From K2

First Author: Venner, Alexander
Instruments: HARPS
ProgramIDs: 072.C-0488, 085.C-0019
BibCode: 2026ApJ...997L..38V

The transit method is currently one of our best means for the detection of potentially habitable "Earth-like" exoplanets. In principle, given sufficiently high photometric precision, cool Earth-sized exoplanets orbiting Sun-like stars could be discovered via single transit detections; however, this has not previously been achieved. In this work, we report a 10 hr long single transit event which occurred on the V = 10.1 K-dwarf HD 137010 during K2 Campaign 15 in 2017. This transit is comparatively shallow (225 ± 10 ppm) but is detected at high signal-to-noise thanks to the exceptionally high photometric precision achieved for the target. Our analysis of the K2 photometry, historical and new imaging observations, and archival radial velocities and astrometry strongly indicate that the event was astrophysical, occurred on-target, and can be best explained by a transiting planet candidate, which we designate HD 137010 b. The single observed transit implies a radius of 1.06−0.05+0.06R⊕ , and assuming negligible orbital eccentricity we estimate an orbital period of 355−59+200 days ( a=0.88−0.10+0.32 au), properties comparable to Earth. We project an incident flux of 0.29−0.13+0.11I⊕ , which would place HD 137010 b near the outer edge of the habitable zone. This is the first planet candidate with Earth-like radius and orbital properties transiting a Sun-like star bright enough for substantial follow-up observations.

A deep ALMA Band 3 survey of HDFS/MUSE3D: Survey description and initial results

First Author: Messias, Hugo
Instruments: ALMA_Band_3
ProgramIDs: 2022.A.00034.S
BibCode: 2026A&A...706A.236M

Context. After more than 10 years of ALMA operations, the community interest in conducting deep extra-galactic millimetre surveys resulted in varying strategic compromises between areal size and map depth to survey the sky. The current bias leans towards a galaxy population found in the field or towards rich starbursty proto-cluster groups, which are both tendentiously surveyed at coarse spatial resolutions. Aims. We describe a survey that addresses these biases. A deep 3 mm survey was conducted with ALMA at long baselines in a 1 × 1 arcmin² region in the Hubble Deep Field South (HDFS) that was also covered by the Multi Unit Spectroscopic Explorer (MUSE) in order to assess resolved molecular gas properties in galaxies in group environments at z > 1. Methods. ALMA observations comprising a four-pointing mosaic with a single band 3 (3 mm) spectral tuning were conducted to cover CO transitions from different groups identified by MUSE. This work consists of a total effective on-source time of 61 hours in configurations with baselines up to 15 km. Results. The final dataset yields an angular resolution of 0.15″─0.2″ (depending on the imaging weights) and maximum recoverable scales of 1″─2″. The final continuum map reaches an unprecedented sensitivity of RMS ∼ 2 μJy/beam, which allowed us to detect three sources at 3 mm (only one of which with multi-wavelength counterparts from the rest-frame UV to radio). Moreover, we detected six line emitters associated with CO J = 2 − 1 at z_spec = 1.284, one of which was not previously detected by MUSE, and none of which was detected in 3 mm continuum. The inter-stellar medium gas masses range from ∼2 × 10⁹ to ∼9 × 10¹⁰ M_⊙ (adopting α_CO = 4 M_⊙/(K.km/s.pc²), including helium). This galaxy group is quite diverse overall, and no two galaxies are alike. Some are clearly offset physically with respect to Hubble imaging that traces the rest-frame ultra-violet emission. We also derived cosmic molecular gas mass densities using this sample as a reference for group environments and found that their densities are similar to that of the galaxy population found in field environments.

Escaping Ionizing Photons from Massive Spiral Galaxies at z ∼ 1

First Author: Maulick, Soumil
Instruments: MUSE
ProgramIDs: 1101.A-0127, 096.A-0045, 095.A-0010, 094.A-0289
BibCode: 2026ApJ...998..242M

We report the detection of Lyman continuum (LyC) photons from three massive (M_* > 10¹⁰ M_⊙) spiral galaxies at a redshift of nearly 1 in the AstroSat UV Deep Field South. Notably, all three systems are viewed at low inclination (i.e., nearly face-on), prompting an investigation into the role of galaxy orientation in the detectability of LyC emission from disk systems. Two of the three galaxies, however, host active galactic nuclei, adding complexity to the interpretation of the LyC signal. We present a detailed analysis of the likely star-forming case and report tentative evidence that a face-on viewing angle may enhance the likelihood of LyC detection in disk galaxies. This represents the first detection of LyC emission from well-characterized spiral galaxies at high redshift, offering a new window into LyC escape mechanisms in such systems. Our findings highlight the need to consider geometric factors and anisotropic escape pathways facilitated by feedback processes alongside more traditional density-bounded scenarios that imply isotropic escape.

The Hidden Story of Chemical Evolution in Local Star-forming Nuclear Rings

First Author: Sextl, Eva
Instruments: MUSE
ProgramIDs: 096.B-0057, DataDoiProID
BibCode: 2026ApJ...997..329S

A Very Large Telescope/MUSE population synthesis study of metallicities in the nuclear star-forming rings of four disk galaxies (NGC 613, NGC 1097, NGC 3351, NGC 7552) is presented. Disentangling the spectral contributions of young and old stellar populations, we find a large spread of ages and metallicities of the old stars in the nuclear rings. This indicates a persistent infall of metal-poor gas and ongoing episodic star formation over many Gyr. The young stars have metallicities a factor two to three higher than solar in all galaxies except NGC 3351, where the range is from half to twice solar. Previously reported detections of extremely metal-poor regions at young stellar age on the rings of these four galaxies are a methodological artifact of the average over all stars, young and old. In addition, it is important to include contributions of very young stars (<6 Myr) in this environment. For each of the four galaxies, the extinction maps generated through our population synthesis analysis provide support for the infall scenario. They reveal dust lanes along the leading edges of the stellar bars, indicating the flow of interstellar material toward the circumnuclear zone. Prominent stellar clusters show little extinction, most likely because of the onset of stellar winds. Inside and on the nuclear rings, regions that are largely free of extinction are detected.

Exomoon search with VLTI/GRAVITY around the substellar companion HD 206893 B

First Author: Kral, Q.
Instruments: GRAVITY
ProgramIDs: 1103.B-0626, 113.26D9, 105.20T0, 1104.C-0651, 109.22ZA, 114.27UV
BibCode: 2026A&A...705A.217K

Context. This study presents the first application of high-precision astrometry to search for exomoons around substellar companions, as this field remains largely unexplored. Aims. We investigate whether the orbital motion of the companion HD 206893 B exhibits astrometric residuals consistent with the gravitational influence of an exomoon or binary planet. Methods. Using the VLTI/GRAVITY instrument, we monitored the astrometric positions of HD 206893 B and c on short (days to months) and long (yearly) timescales. This enabled us to isolate potential residual wobbles in the motion of component B attributable to an orbiting moon. Results. Our analysis reveals tentative astrometric residuals in the HD 206893 B orbit. If interpreted as an exomoon signature, these residuals correspond to a candidate (HD 206893 B I) with an orbital period of approximately 0.76 years and a mass of ~0.4 Jupiter masses. However, the origin of these residuals remains ambiguous and could be due to systematics. Complementing the astrometry, our analysis of GRAVITY R = 4000 spectroscopy for HD 206893 B confirms a clear detection of water, but no CO was found using cross-correlation. We also found that AF Lep b, and β Pic b are the best short-term candidates to look for moons with GRAVITY+. Conclusions. Our observations demonstrate the transformative potential of high-precision astrometry in the search for exomoons and proves the feasibility of the technique to detect moons with masses lower than Jupiter and potentially down to less than Neptune in optimistic cases. Crucially, further high-precision astrometric observations with VLTI/GRAVITY are essential to verify the reality and nature of this signal and apply this technique to a range of planetary systems.

Direct imaging of mass transfer and circumcompanion structures in π¹ Gru with VLTI/MATISSE

First Author: Drevon, J.
Instruments: MATISSE
ProgramIDs: 108.22E9
BibCode: 2026A&A...706L...1D

Aims. We investigate how the presence of a binary companion appears to affect dust and molecule formation in the circumstellar environment of a star on the asymptotic giant branch (AGB). Methods.L- and N-band observations obtained over the course of one month with the multi aperTure mid-infrared spectroScopic experiment instrument (MATISSE) at the very large telescope interferometer (VLTI) were used to constrain the distribution of dust and molecules in the close environment of π¹ Gru through image reconstruction. The reconstructed images were fit to the interferometric observables, that is, the visibilities and closure phases, using the two Python-based tools Python for MiRA (PYRA) and mean astrophysical images with PYRA (MYTHRA) built around the multi-aperture image reconstruction algorithm (MiRA). Results. Our observations support (i) a wind Roche-lobe overflow (WRLOF) scenario, where mass transfer from the AGB star to its companion produces a possible circumcompanion disk in the L band around π¹ Gru C, with a central cavity that likely traces dust sublimation and a circumcompanion envelope in the N band. (ii) A main-sequence nature for the companion: Because both Atacama large millimeter/submillimeter array (ALMA) and the VLTI/MATISSE N-band observations show emission, we favor a thermal infrared emission from the main-sequence star over free-free emission from a with dwarf companion. Finally, (iii) a plume-like structure extending from π¹ Gru C, likely marking the onset of the spiral observed at larger scales. Together, this provides direct evidence that links small-scale mass transfer and disk formation through WRLOF to the global circumstellar morphology. Conclusions. These results highlight the atmospheric deformation induced by the companion, reveal ongoing mass transfer between the evolved star and its companion, and indicate a circumcompanion disk-like structure.

Gaia FGK benchmark stars: Spectral library and abundances of α and Fe-peak elements of the third version

First Author: Casamiquela, L.
Instruments: FEROS, FLAMES, HARPS, UVES
ProgramIDs: 112.26WR, 69.D-0169, 71.B-0529, 71.D-0370, 60.A-9709, 072.C-0033, 072.D-0107, 073.C-0528, 074.B-0455, 074.D-0016, 078.C-0378, 080.D-2002, 082.C-0446, 087.C-0476, 087.D-0781, 088.C-0498, 088.C-0892, 089.C-0471, 60.A-9120, 60.A-9122, 60.A-9700, 072.B-0585, 073.B-0607, 074.B-0639, 074.C-0134, 075.D-0453, 076.B-0055, 076.B-0133, 077.D-0035, 082.C-0218, 083.D-0871, 085.B-0847, 085.C-0062, 086.C-0098, 086.D-0082, 087.B-0308, 088.C-0879, 089.D-0202, 090.B-0605, 092.C-0178, 092.D-0207, 093.C-0343, 093.C-0929, 095.C-0437, 096.C-0092, 097.C-0409, 188.B-3002, 193.B-0936, 266.D-5655, 273.D-5032, 290.C-5196, 380.C-0083, 383.C-0806, 65.L-0507, 67.C-0206, 67.D-0298, 67.D-0439, 68.C-0548, 68.D-0094
BibCode: 2026A&A...705A.167C

Context. Accurate determination of the chemical abundances in stars plays a pivotal role in understanding stellar structure and evolution, nucleosynthesis, and the chemical enrichment history of the Milky Way. Benchmark stars with precise and accurate atmospheric parameters and abundances are indispensable for calibrating spectroscopic surveys and testing stellar atmosphere models. Aims. This study focuses on the compilation of high-quality spectra and the determination of chemical abundances of iron-peak and α elements for the third version of the Gaia FGK benchmark stars (GBSv3). Methods. We compiled spectra of the GBSv3 from public archives and complemented these with our observations. We used fundamental atmospheric parameters to perform a spectroscopic analysis using the public code iSpec and derived the chemical abundances. Results. We compiled a homogeneous spectral library of high-resolution (42 000) and high signal-to-noise (>100) normalised spectra for 202 stars, including the 192 GBSv3, nine stars with indirect measurement of the angular diameter from previous Gaia FGK benchmark versions, and the Sun. Using four radiative transfer codes, we derived chemical abundances of 13 chemical species (Fe I, Fe II, Mg I, Si I, Ca I, Ti I, Ti II, Sc II, V I, Cr I, Mn I, Co I, Ni I). We performed an in-depth study of several sources of error. Conclusions. The GBSv3 contributes to the legacy samples of spectroscopic reference stars through improved statistics and homogeneity. This work offers the community a homogeneous spectral library and robust reference abundances for iron-peak and α elements, supported by an extensive analysis of the associated uncertainties.

COSMOS-3D: Dense Circumnuclear Gas Across Black Hole Growth Phases at z ∼ 3

First Author: Li, Zi-Jian
Instruments: ALMA_Band_3, ALMA_Band_4, ALMA_Band_6, ALMA_Band_7
ProgramIDs: 2021.1.00225.S, 2023.1.00180.L, 2021.1.01328.S, 2016.1.01012.S, 2016.1.01001.S
BibCode: 2026ApJ..1002....9L

We report the discovery of two broad-line X-ray active galactic nuclei (AGNs) (cid_414 and cid_947) at z ∼ 3 identified in the JWST Cycle 3 COSMOS-3D program using NIRCam F444W grism spectroscopy. Both exhibit prominent He Iλ10830 +Paγ emission and absorption, indicative of circumnuclear dense gas that is traced in these systems. Complementary UV and optical spectroscopy in the COSMOS field provides Lyα, Si IV, and C IV measurements. Both sources are detected in MIRI F1000W, and cid_414 is also detected in F2100W, indicating hot dust emission. The two AGNs show distinct black hole and obscuration properties. The source cid_414 displays little red dot (LRD)-like, V-shaped spectral energy distribution with a turnover near the Balmer 4000 Å break and a narrow Lyα line with logLLyα=42.49±0.01ergs−1 , with no additional metal lines detected. In contrast, cid_947 exhibits a higher He Iλ10830 absorption column density, larger X-ray─inferred N_H, lower intrinsic 2─10 keV luminosity, and strong blueshifted features in He I, Si IV, and C IV absorption with velocity offsets exceeding 5000 km s⁻¹. Photoionization modeling implies gas densities of ∼10⁹⁻¹⁰ cm⁻³ and sizes comparable to the broad-line region, consistent with dense gas envelopes predicted for LRDs. Together with previous detections of He Iλ10830 absorption in compact LRDs, these results suggest that dense circumnuclear gas is likely prevalent at high redshift and may regulate obscuration and black hole─host coevolution across AGN types.

WISDOM project ─ XXVIII. Molecular gas measurement of the supermassive black hole mass of the galaxy NGC 1387

First Author: Dominiak, Pandora
Instruments: ALMA_Band_6
ProgramIDs: 2016.1.00437.S, 2016.2.00053.S
BibCode: 2026MNRAS.548ag546D

Supermassive black hole (SMBH) masses can be measured using molecular gas kinematics. Here we present high-angular-resolution (0.12 arcsec or

$\approx 11$

pc) Atacama Large Millimeter/submillimeter Array observations of the

$^{12}$

CO(2─1) line emission of the early-type galaxy NGC 1387. The observations reveal a face-on, regularly rotating central molecular gas disc with a diameter of

$\approx 18$

arcsec (

$\approx 1.7$

kpc) and a central depression slightly larger than the SMBH sphere of influence. We forward model the CO data cube in a Bayesian framework with the KINEMATIC MOLECULAR SIMULATION code, and use Hubble Space Telescope data to constrain the stellar gravitational potential contribution to the molecular gas kinematics. We infer an SMBH mass of

$1.10^{+1.71}_{-0.95}[\text{stat},3\sigma ]^{+2.45}_{-1.09}[\text{sys}]\times 10^8$

$_\odot$

and an F160W-filter stellar mass-to-light ratio of

$0.90^{+0.44}_{-0.35}[\text{stat}, 3\sigma ]^{+0.46}_{-0.36}[\text{sys}]$

$_\odot$

$_{\odot ,\text{F160W}}$

. This SMBH mass is consistent with the SMBH mass─stellar velocity dispersion relation.

Exploring the connection between compact object mergers and fast X-ray transients: The cases of LXT 240402A and EP250207b

First Author: Becerra, R. L.
Instruments: FORS2, HAWKI
ProgramIDs: 114.27LW, 110.24CF
BibCode: 2026A&A...705A.233B

Context. The connection between compact object mergers and some extragalactic fast X-ray transients (FXRTs) has long been hypothesised but never ultimately established. Aims. In this work, we investigate two FXRTs, the LEIA X-ray Transient LXT 240402A and the Einstein Probe EP 250207b, whose precise positions lie close to nearby (z ≲ 0.1) quiescent galaxies with a negligible probability of chance coincidence, identifying them as particularly promising cases of merger-driven explosions in the local Universe. Methods. We used Chandra to derive accurate localisations for both events and secure otherwise ambiguous associations with their optical counterparts. Deep optical and near-infrared observations with VLT, GTC, and LBT were performed to characterise the surrounding environment and search for kilonova emission, the hallmark of neutron star mergers. Complementary early-time X-ray monitoring with Swift and Einstein Probe was used to constrain the non-thermal afterglow. Results. We find that both FXRTs remain compatible with a compact binary merger progenitor, which produced low-mass ejecta and kilonova emission subdominant to the afterglow. However, alternative explanations such as a distant (z ≳ 1) core-collapse supernova cannot be conclusively ruled out.

TOI-333b: A Neptune-desert planet around an F7V star

First Author: Alves, Douglas R.
Instruments: HARPS, NACO
ProgramIDs: 109.2374, 113.26GX, 112.25QD, 0103.C-0449
BibCode: 2026A&A...705A.210A

Observations have shown that planets similar to Neptune are rarely found orbiting Sun-like stars with periods up to ∼4 days. This defines the so-called Neptune desert region. The detection of each individual planet in this region therefore holds a high value by providing detailed insights into the formation and evolution of this population. We report the detection of TOI-333b, a Neptune-desert planet with a mass, radius, and bulk density of 20.1 ± 2.4 M_⊕, 4.26 ± 0.11 R_⊕, and 1.42 ± 0.21 g cm⁻³. The planet orbits an F7V star every 3.78 d, whose mass, radius, and effective temperature are of 1.2 ± 0.1 M_⊙, 1.10 ± 0.03 R_⊙, and 6241₋₆₂⁺⁷³ K, respectively. TOI-333bis likely younger than 1 Gyr, which is supported by the doublet Li line around 6707.856 Å and its comparison to Li abundances in open clusters with well-constrained ages. The planet is expected to host only a 8.5_−8.3^+10.9% gas-to-core mass ratio for an H/He envelope. On the other hand, models of irradiated ocean worlds predict a 20₋₁₀⁺¹¹% H₂O mass fraction with a core fraction of 35₋₂₃⁺²⁰%. We therefore expect that the internal composition of TOI-333bis dominated by a pure rocky composition with almost no H/He envelope, or a rocky world with almost equal mass fraction of water. Finally, TOI-333bis more massive and larger than 77% and 82% of its Neptune-desert counterparts, and its host ranks among the hottest known stars for Neptune-desert planets. This makes this system a unique laboratory for studying the evolution of these planets around hot stars.

Discovery of an Extremely Luminous Type II Cepheid in the Andromeda Giant Stellar Stream: Evidence for a Hierarchical Triple with an Inner Binary Merger

First Author: Chen, Pinjian
Instruments: FEROS
ProgramIDs: DataDoiProID
BibCode: 2026ApJ...997L..24C

We report the discovery of LAMOST J0041+3948, the most luminous post-asymptotic giant-branch (AGB) Type II Cepheid known, located in the Andromeda Giant Stellar Stream. Its spectral energy distribution (SED) exhibits a strong near-infrared excess, indicating the presence of a circumbinary dusty disk and hence binarity. SED fitting yields an effective temperature of Teff=6738−262+234 K and a post-AGB luminosity of log(L/L⊙)=4.32−0.08+0.07 . Comparison with theoretical evolutionary tracks suggests a ∼2.0─4.0 M_⊙ progenitor when accounting for a possible scattered-light contribution. Zwicky Transient Facility light curves reveal a pulsation period of 89 days that lies close to the period─luminosity relation for long-period RV Tauri stars. Follow-up spectroscopy reveals clear s-process enrichment and signatures consistent with an accretion disk around the companion. The inferred progenitor is significantly younger and more massive than a typical stream member, suggesting that an additional mechanism, such as a stellar merger, is required. We propose a formation channel in which the present post-AGB binary descends from a hierarchical triple system. In this scenario, the inner binary merged after the system was displaced to its current location by the galaxy merger event, and the resulting massive merger remnant subsequently evolved into the extremely luminous post-AGB star observed today.

Kinematic and extinction analysis of a potential spiral arm beyond the Galactic bar

First Author: Joharle, Simran
Instruments: VIRCAM
ProgramIDs: 179.B-2002
BibCode: 2026A&A...705A.131J

Context. Determining the structure of the Milky Way is essential for understanding its morphology, dynamics, and evolution. However, studying its innermost regions is challenging due to high extinction and crowding. The detection of a double red clump (RC; core-helium-burning stars) feature at very low Galactic latitudes suggests the presence of a spiral arm beyond the Galactic bar, providing new insights into the Galaxy's structure along this complex line of sight. Aims. We aim to evaluate the presence of this spiral arm by analysing the proper motion and extinction distributions of the detected RC features. Methods. We constructed proper motion and extinction difference maps to investigate the kinematic and reddening properties of the RC populations. We also confirmed the kinematic difference we see in observational data with N-body simulations of a Milky Way-like galaxy. Results. We find that the two RC features are kinematically distinct, with a relative proper motion difference of −0.16 ± 0.02 mas/yr in the component parallel to the Galactic plane. This difference can be explained by Galactic rotation if the two RC features are located at different distances along the line of sight, consistent with our simulation results. The extinction towards the secondary RC is also ~0.05 mag higher than that of the primary RC. Additionally, we estimate that the extinction difference between the RC features corresponds to only ~5% of the total extinction from Earth to the first RC, suggesting little interstellar material between the farthest edge of the Galactic bar and the kinematically distinct structure traced by the secondary RC. As a secondary result, we derived the extinction curve using JK_s photometry, obtaining A_J/A_{K_s} = 3.34 ± 0.07, consistent with previous studies of the innermost Milky Way. We find no significant variation of the extinction curve across fields or along the line of sight, within the uncertainties. The results are compatible with the secondary clump stars belonging to the spiral arm, although we cannot exclude that the population belongs to the disc.

The relationship between warm and hot gas-phase metallicity in massive elliptical galaxies and the influence of active galactic nucleus feedback

First Author: Olivares, Valeria
Instruments: MUSE
ProgramIDs: 095.B-0127, 094.A-0859, 60.A-9312, 0102.B-0048, 097.A-0366, 0103.A-0447, 097.A-0909
BibCode: 2026A&A...705A.249O

Context. Warm ionized gas is ubiquitous at the centers of X-ray bright elliptical galaxies. While it is believed to play a key role in the feeding and feedback processes of supermassive black holes, its origins remain under debate. Existing studies have primarily focused on the morphology and kinematics of warm ionized gas. Aims. This work aims to provide a new perspective on warm (∼10 000 K) ionized gas and its connection to X-ray-emitting hot gas (> 10⁶ K) by measuring and comparing their metallicities. Methods. We conducted a joint analysis of 13 massive elliptical galaxies using MUSE/VLT and Chandra observations. Emission-line ratios, including [OIII]/Hβ, [NII]/Hα, were measured using MUSE observations to infer the ionization mechanisms. We derive metallicities of the warm ionized gas using HII, and LINER calibrations. We also computed the warm phase metallicity using X-ray/EUV, and pAGB star models. For two sources at higher redshifts, the direct T_e method was also used to measure warm gas metallicities. The metallicity of the hot gas was measured using Chandra X-ray observations. Results. Our observations reveal that most sources exhibit composite ionization, with contributions from both star formation and LINER-like emission. The four sources with the lowest star formation rates in our sample ─ Centaurus, M87, M84, and Abell 496 ─ are dominated by LINER emission. A positive linear correlation was found between the gas-phase metallicities of the warm and hot phases, ranging from 0.3 to 1.5 Z_⊙. In some sources the warm gas metallicity shows a central drop. A similar radial trend has been reported for the hot gas metallicity in some galaxy clusters. Conclusions. The ionization mechanisms of cooling flow elliptical galaxies are diverse, suggesting multiple channels for powering the warm ionized gas. The positive correlation found in warm and hot gas metallicities suggest the intimate connection between the two gas phases, likely driven by gas cooling and/or mixing. The large variation in the warm gas metallicity further suggests that cold gas mass derived under the assumption of solar metallicity for the CO-to-H₂ conversion factor needs to be revised by approximately an order of magnitude.

Consensus-based algorithm for the nonparametric detection of star clusters (CANDiSC)

First Author: Obasi, C. O.
Instruments: VIRCAM
ProgramIDs: 179.B-2002, 198.B-2004
BibCode: 2026A&A...705A.244O

Context. The VISTA Variables in the Vía Láctea (VVV) and its eXtension (VVVX) are near-infrared surveys mapping the Galactic bulge and adjacent disk. These datasets have enabled the discovery of numerous star clusters obscured by high and spatially variable extinction. However, most previous searches relied on visual inspection of individual tiles, which is inefficient and biased against faint or low-density systems. Aims. We aim to develop an automated, homogeneous algorithm for systematic cluster detection across different surveys. Here, we aim to apply our method to VVVX data covering low-latitude regions of the Galactic bulge and disk, affected by extinction and crowding. Methods. We introduce the Consensus-based Algorithm for Nonparametric Detection of Star Clusters (CANDiSC), which integrates kernel-density estimation (KDE), Density-Based Spatial Clustering of Applications with Noise (DBSCAN), and nearest-neighbor density estimation (NNDE) within a consensus framework. A stellar overdensity is classified as a candidate if identified by at least two of these methods. We applied CANDiSC to 680 tiles in the VVVX PSF photometric catalogue, covering ≍ 1100, deg². Results. We detect 163 stellar overdensities, of which 118 are known clusters. Cross-matching with recen catalogues yields five additional matches, leaving 40 likely new candidates absent from existing compilations. The estimated false-positive rate is below 5%. Conclusions. CANDiSC offers a robust and scalable approach for detecting stellar clusters in deep, near-infrared surveys, successfully recovering known systems and revealing new candidates in the obscured and crowded regions of the Galactic plane.

The HST-Hyperion Survey: Companion fraction and overdensity in a z ∼ 2.5 proto-supercluster

First Author: Giddings, F.
Instruments: VIMOS, VIRCAM
ProgramIDs: 185.A-0791, 175.A-0839, 179.A-2005
BibCode: 2026A&A...706A..55G

We present a study of the galaxy merger and interaction activity within the Hyperion Proto-supercluster at z ∼ 2.5 in an effort to assess the occurrence of galaxy mergers and interactions in contrast to the coeval field and their impact on the buildup of stellar mass in high-density environments at higher redshifts. For this work, we utilized data from the Charting Cluster Construction with VUDS and ORELSE Survey (C3VO) along with extensive spectroscopic and photometric datasets available for the COSMOS field ─ including the HST-Hyperion Survey. To evaluate potential merger and interaction activity, we measured the fraction of galaxies with close kinematic companions (f_ckc) both within Hyperion and the coeval field by means of a Monte Carlo (MC) methodology developed in this work that probabilistically employs our entire combined spectroscopic and photometric dataset. We validated our f_ckc MC methodology on a simulated lightcone built from the GAlaxy Evolution and Assembly (GAEA) semi-analytic model, and we determined correction factors that account for the underlying spectroscopic sampling rate of our dataset. We find that galaxies in Hyperion have close kinematic companions ≳2.5× more than galaxies in the field and measure a corrected f_ckc = 59⁺⁹₋₁₀ 59 − 10 + 9 % for Hyperion and a corrected f_ckc = 23^+1.7_−1.8 23 − 1.8 + 1.7 % for the surrounding field; a ≳3σ difference. The enhancement in f_ckc likely correlates to an enhancement in the merger and interaction activity within the high-density environment of Hyperion and matches the trend seen in other structures. The rate of merger and interactions within the field implied from our field f_ckc measurement is well aligned with values measured from other observations in similar redshift ranges. The enhanced f_ckc measured within Hyperion suggests that merger and interaction activity play an important role in the mass growth of galaxies in denser environments at higher redshifts.

Revisiting the unification of tidal disruption events with polarimetry

First Author: Wichern, H. C. I.
Instruments: EFOSC2, FORS2
ProgramIDs: 112.25JQ, 106.216C, 199.D-0143, 111.24ME, 0103.D-0350, 106.214S, 108.222Q, 109.23FR
BibCode: 2026A&A...705A.250W

Aims. Tidal disruptions of stars by supermassive black holes produce emission at different wavelengths, but the optical emission is of ambiguous origin. A unification scenario of tidal disruption events (TDEs) has been proposed to explain the different classes of X-ray and optically selected events by introducing a dependence on the viewing angle and geometry. This work aims to test the unification scenario among optically bright TDEs using polarimetry. Methods. By studying the optical linear polarisation of nineteen TDEs (nine of which are newly analysed in this work), we placed constraints on their photosphere geometry, inclination, and the emission process responsible for the optical radiation. We also investigated how these properties correlate with the relative X-ray brightness of the events, quantified by the L_X/L_g ratio. Results. We find that 14 of the 16 non-relativistic events can be accommodated by the unification model. The continuum polarisation levels of the non-relativistic TDEs most often lie in the range P ∼ 1 − 2% (13 events), and for all except one event, they remain below 6%. For those optical TDEs that have multiple epochs of polarimetry, the continuum polarisation levels decrease with time after peak light for five of the ten events, increase for three events, and stay approximately constant for two events. When observed after +70 days (7/16 events), they become consistent with zero polarisation within uncertainties (5/7 events). This implies that the photosphere geometries of TDEs are at least initially asymmetric and evolve rapidly, which if tracing the formation of the accretion disc, suggests efficient circularisation. The polarisation signatures of emission lines of seven TDEs directly support a scenario in which optical light is reprocessed in an electron-scattering photosphere. TDEs are most often weak in X-rays when significantly polarised. However, a subset of events deviates from the unification model to some extent, suggesting this model may not fully capture the diverse behaviour of TDEs. Multi-epoch polarimetry plays a key role in understanding the evolution and emission mechanisms of TDEs.

JWST spectroscopic confirmation of the Cosmic Gems arc at z = 9.625: Insights into the small-scale structure of a post-burst system

First Author: Messa, M.
Instruments: MUSE
ProgramIDs: 112.25TF
BibCode: 2026A&A...705A.173M

We present JWST/NIRSpec integral field spectroscopy of the Cosmic Gems arc, strongly magnified by the galaxy cluster SPT-CL J0615−5746. Six-hour integration using NIRSpec prism spectroscopy (resolution R ≃ 30 − 300), covering the spectral range 0.8 − 5.3 μm, reveals a pronounced Lyα-continuum break at λ ≃ 1.3 μm, as well as weak optical Hβ and [O III] λ4959 emission lines at z = 9.625 ± 0.002, located in the reddest part of the spectrum (λ > 5.1 μm). No additional ultraviolet or optical emission lines are reliably detected. A weak Balmer break is measured alongside a very blue ultraviolet slope (β ≤ −2.5, F_λ ∼ λ^β). Spectral fitting with Bagpipes suggests that the Cosmic Gems galaxy is in a post-starburst phase, making it the highest-redshift system currently observed in a mini-quenched state. Spatially resolved spectroscopy at tens of parsecs shows relatively uniform features across subcomponents of the arc. These findings align well with the physical properties previously derived from JWST/NIRCam photometry of the stellar clusters, now corroborated by spectroscopic evidence. In particular, five observed star clusters exhibit ages of 7 − 30 Myr. An updated lens model constrains the intrinsic sizes and masses of these clusters, confirming they are extremely compact and denser than typical star clusters in local star-forming galaxies (Σ_{M_★} = 10⁵ − 10⁶ M_⊙). Additionally, four compact stellar systems consistent with star clusters (≲10 pc) are identified along the extended tail of the arc. A sub-parsec line-emitting HII1.2ex region straddling the critical line, lacking a NIRCam counterpart, is also serendipitously detected. The Cosmic Gems arc thus offers a rare opportunity to investigate, at parsec scales, the aftermath of a star formation burst in the early Universe.

Astrometric view of companions in the inner dust cavities of protoplanetary discs

First Author: Vioque, Miguel
Instruments: ALMA_Band_3, ALMA_Band_4, ALMA_Band_6, ALMA_Band_7, ALMA_Band_8
ProgramIDs: 2012.1.00631.S, 2012.1.00698.S, 2013.1.00291.S, 2013.1.00437.S, 2015.1.00979.S, 2015.1.01301.S, 2015.A.00005.S, 2016.1.00344.S, 2016.1.00484.L, 2016.1.00715.S, 2016.1.01164.S, 2016.1.01286.S, 2016.1.01344.S, 2016.1.01511.S, 2017.1.00388.S, 2017.1.00449.S, 2017.1.00492.S, 2017.1.00969.S, 2017.1.01151.S, 2017.1.01404.S, 2017.1.01460.S, 2017.1.01578.S, 2017.1.01631.S, 2017.1.01678.S, 2018.1.00028.S, 2018.1.00310.S, 2018.1.00350.S, 2018.1.00532.S, 2018.1.00536.S, 2018.1.00689.S, 2018.1.01020.S, 2018.1.01054.S, 2018.1.01055.L, 2018.1.01066.S, 2018.1.01255.S, 2018.1.01302.S, 2018.1.01309.S, 2018.1.01458.S, 2018.1.01755.S, 2018.1.01829.S, 2018.A.00030.S, 2019.1.00566.S, 2019.1.00607.S, 2019.1.00847.S, 2019.1.01059.S, 2019.1.01091.S, 2019.1.01210.S, 2019.1.01270.S, 2021.1.00128.L, 2021.1.00378.S, 2021.1.00709.S, 2021.1.00994.S, 2021.1.01123.L, 2021.1.01137.S, 2021.1.01661.S, 2021.1.01705.S, 2022.1.00154.S, 2022.1.00313.S, 2022.1.00340.S, 2022.1.00646.S, 2022.1.00742.S, 2022.1.00760.S, 2022.1.00908.S, 2022.1.01302.S
BibCode: 2026A&A...705A.238V

Context. Protoplanetary discs with inner dust cavities (often referred to as 'transition discs') are potential signposts of planet formation. However, few companions have been identified within these cavities, and the role of companions in shaping them remains unclear. Aims. We used Gaia astrometry to search for planetary and stellar companions in a sample of 98 transition discs, assessing the occurrence rate of such companions and their potential influence on cavity formation. Methods. For the 98 young stellar objects (YSOs) with inner dust cavities, we computed Gaia proper motion anomalies, which together with the renormalised unit weight error (RUWE), identify companions with mass ratios q ≳0.01 at ∼0.1−30 au. We assessed the impact of disc gravity, accretion, disc-scattered light, dippers, starspots, jets, and outflows on the measured proper motion anomalies, concluding that these effects are unlikely to affect our analyses and that astrometric techniques such as the one of this work can be robustly applied to YSOs. Results. Significant proper motion anomalies are found in 31 transition discs (32% of the sample), indicative of companions. We recovered 85% of the known companions within our sensitivity range. Assuming that the astrometry of each system is dominated by a single companion, we modelled the semi-major axis and mass required to reproduce the observed astrometric signals. Most inferred companions have M>30 M_J, placing many within or near the stellar mass regime. Seven sources host companions compatible with a planetary mass (M<13 M_J, HD 100453, J04343128+1722201, J16102955-3922144, MHO6, MP Mus, PDS 70, and Sz 76). For the non-detections, we provide the companion masses and semi-major axes that can be excluded in future searches. About half (53%) of detected companions cannot be reconciled with having carved the observed dust cavities. Conclusions. We have gathered evidence of the presence of companions in a large sample of transition discs. However, we find that the population of transition discs cannot be fully described as a circumbinary population. Transition discs host as many companions within our sensitivity range as do randomly sampled groups of YSOs and main-sequence stars. If dust cavities are shaped by companions, such companions must reside at larger orbital separations than those of the companions detected here, and we predict them to be of planetary mass.

The ALMA-QUARKS Survey: Evidence of an Explosive Molecular Outflow in IRAS 15520─5234

First Author: Hoque, Ariful
Instruments: ALMA_Band_6
ProgramIDs: 2021.1.00095.S
BibCode: 2026ApJ..1001..161H

We present a study of the massive protocluster IRAS 15520─5234, which displays evidence of an explosive molecular outflow that unleashed a kinetic energy of at least 10⁴⁸ erg. The protocluster contains 16 dense cores detected in the Atacama Large Millimeter/submillimeter Array (ALMA) band 6 continuum emission maps, having masses in the range from 0.2 to 11.0 M_⊙. Our analysis of CO (2−1) emission reveals 28 well-collimated outflow fingers, the majority of which follow a Hubble─Lemaître velocity law. The outflow fingers show no preferred orientation in the plane of sky and emerge from a common center of origin. We estimate the total mass, momentum, and kinetic energy of the outflow fingers and find that the values are at least 1 order of magnitude higher than the typical bipolar outflows associated with massive protostars. The morphology and kinematics of the outflow fingers suggest that the outflow associated with IRAS 15520─5234 is explosive in nature. We calculate the dynamical age of the explosive event to be approximately 6550 yr. Additionally, we estimate the frequency of such explosive outflows in the Galaxy, which is one event every 83 yr. Finally, we speculate that the rearrangement of masses within the massive protocluster and the dynamical interaction among the massive cores may result in the formation of such an energetic event.

Protostellar Outflows Shed Light on the Dominant Close Companion Star Formation Pathways

First Author: Sponzilli, Ryan
Instruments: ALMA_Band_6
ProgramIDs: 2017.1.00053.S, 2018.1.01038.S
BibCode: 2026ApJ..1001..134S

Understanding the formation pathway for close-companion protostars is central to unraveling the processes that govern stellar multiplicity and very early star formation. We analyze a large sample of 51 Class 0/I close-companion protostellar systems, of which 38 show detectable outflows, yielding 42 measured outflows used in our analysis. We use Atacama Large Millimeter/submillimeter Array observations of 11 systems in Perseus and 40 systems in Orion. These companions formed either directly at these small scales (≲500 au separations) via disk fragmentation or at larger scales (>1000 au separations) via turbulent fragmentation followed by inward migration. Because of differences in formation mechanism, the former is expected to have preferentially aligned disks and outflows, whereas the latter is expected to show no preferred alignment. The relative prevalence of these formation pathways remains uncertain, yet it is critical to forming a comprehensive picture of star formation. We examine the distribution of position angles (PAs) of companion protostars relative to the PAs of their molecular outflows. The outflow, as traced by ¹²CO (J = 2 → 1), is a useful proxy for the angular momentum of the system, expected to be orthogonal to the binary orbital plane. We use a simple model to account for a random sampling of inclination and orbital phase in each system, finding that the observations are consistent with a distribution where the outflows are preferentially orthogonal to the companions. Based on this analysis, we suggest disk fragmentation is the dominant formation pathway for close-companion protostellar systems.

Stratification of the Active Galactic Nucleus─Driven Multiphase Outflows in the Dwarf Seyfert Galaxy NGC 4395

First Author: Nandi, Payel
Instruments: ALMA_Band_6
ProgramIDs: 2017.1.00572.S
BibCode: 2026ApJ..1001..226N

We present a multiwavelength study of nuclear outflows in the nearby dwarf Seyfert galaxy NGC 4395, which hosts an intermediate-mass black hole. Using JWST/NIRSpec and MIRI integral-field-unit spectroscopy (1.66─28.6 μm), together with Atacama Large Millimeter/submillimeter Array (ALMA) and Gemini/GMOS data, we probe the ionized and molecular gas on parsec scales. The JWST nuclear spectra reveal 134 emission lines, including H I, He, numerous fine-structure lines, H₂ rotational/rovibrational transitions, and several polycyclic aromatic hydrocarbon bands. Modelling of the H₂ rotational lines reveals three warm/hot molecular components (T ≍ 580, 1480, and 2900 K), along with a cold (< 50 K) phase traced by ALMA CO(2─1). Outflow signatures are detected in cold and warm/hot molecular gas, in H I, and in 36 fine-structure lines spanning ionization potentials of 7.6─300 eV. Ionized outflow velocities range from 127 to 716 km s⁻¹, with blueshifted and redshifted components consistent with a stratified biconical geometry. The cold molecular gas shows a mass outflow rate nearly 1─2 orders of magnitude larger than that of the warm/hot molecular and ionized phases. The kinetic coupling efficiency is 0.003%─0.12% for the coronal-line gas and 0.4%─1.4% for the H I outflow, indicating that only the low-ionization gas significantly impacts the surrounding ISM. Outflow velocity and the fraction of flux in the outflowing component increase with ionization potential, implying that the most highly ionized gas originates closest to the active galactic nucleus and is most efficiently accelerated.

Linear filament and nested cluster evolution tomography (LANCET): I. Capture the evolution of dense gas in 14-parsec filament G316.8

First Author: Xu, Fengwei
Instruments: ALMA_Band_6
ProgramIDs: 2016.1.00909.S
BibCode: 2026A&A...708A.251X

A dynamic view of mass assembly is essential for understanding the formation of massive stars and clusters. However, interpreting evolutionary diagnostics from Galactic-wide surveys requires careful consideration of distance and environmental variations. The G316.8 filament provides an excellent controlled case: a 14-parsec, nearly linear structure comprising three contiguous subregions with comparable molecular gas reservoirs (each ~10 000 M_⊙), yet spanning a clear evolutionary sequence from a northern infrared dark cloud (young) through a central massive young stellar object (intermediate), to a southern HII region (evolved). The Linear filament and nested cluster evolution tomography (LANCET) project mapped the entire G316.8 filament with the Atacama Compact Array (ACA) at 1.3 mm, achieving 6″ (0.08 pc) resolution over 26.7 arcmin² (17.1 pc²). By combining ACA 7 m data with Herschel and APEX/ArTéMiS observations, we produced high-resolution temperature and column-density maps. We quantified subregional differences using (i) dense-fragment statistics, (ii) column-density probability distribution functions (N-PDFs), and (iii) the scale-dependent structural diagnostic, the ∆-variance. From young to intermediate to evolved, the maximum fragment mass increases from 8 to 160 to 490 M_⊙, while the dense-gas mass fraction (>0.5 g cm⁻²) rises from 0.4 to 2.3 to 9.6%. Along this sequence, the N-PDF develops a slightly flatter primary power-law tail and an additional, steeper secondary tail; the ∆-variance slope becomes progressively shallower. Across G316.8, the subregional differences consistently indicate a coherent evolutionary trend of massive star formation, in which gas is continuously assembled into sub-parsec dense structures. The forthcoming 12 m array observations are about to extend this dynamic picture by resolving dense core formation and probing gas kinematics and magnetic fields.

B Aur, a Rosetta stone for studies of planet formation: IV. C/O estimates from CS and SO interferometric observations

First Author: Rivière-Marichalar, P.
Instruments: ALMA_Band_6
ProgramIDs: 2019.1.00579.S, 2021.1.00690.S
BibCode: 2026A&A...707A.348R

Context. Protoplanetary disks are the birthplaces of planets. As such, they set the initial chemical abundances available for planetary atmosphere formation. Thus, studying elemental abundances, molecular compositions, and abundance ratios in protoplanetary disks is key to linking planetary atmospheres to their formation sites. Aims. We aim to derive the sulfur abundance and the C/O ratio in the AB Aur disk using interferometric observations of CS and SO. Methods. New NOEMA observations of CS 3─2 toward AB Aur are presented. We used velocity-integrated intensity maps to determine the inclination and position angles. Keplerian masks were constructed for all observed species to assess the presence of non-Keplerian motions. We used the CS/SO ratio to study the C/O ratio. We compared our present and previous interferometric observations of AB Aur with a NAUTILUS disk model to gain an insight into the S elemental abundance and C/O ratio. Results. We derived an observational CS/SO ratio ranging from 1.8 to 2.6. Only NAUTILUS models with C/O≳1 can reproduce such ratios. The comparison with models points to strong sulfur depletion, with [S/H]=8 × 10⁻⁸, but we note that no single model can simultaneously fit all observed species.

The ALMA survey to Resolve exoKuiper belt Substructures (ARKS): IV. CO gas imaging and overview

First Author: Mac Manamon, S.
Instruments: ALMA_Band_6, ALMA_Band_7
ProgramIDs: 2012.1.00142.S, 2012.1.00198.S, 2015.1.01260.S, 2016.1.00104.S, 2016.1.00195.S, 2016.1.00907.S, 2017.1.00167.S, 2017.1.00825.S, 2018.1.01222.S, 2019.1.00189.S, 2022.1.00338.L
BibCode: 2026A&A...705A.198M

Context. CO gas is detected in a significant number (~20) of debris discs (exoKuiper belts), but understanding its origin and evolution remains elusive. Crucial pieces of evidence are its mass and spectro-spatial distribution, which are coupled through optical depth and have only been analysed at low to moderate resolution so far. The ALMA survey to Resolve exoKuiper belt Substructures (ARKS) is the first ALMA large program to target debris discs at high spectro-spatial resolution. Aims. We used ¹²CO and ¹³CO J=3-2 line data of 18 debris belts observed by ARKS, 5 of which were already known to be gas-bearing, in order to analyse the spectro-spatial distribution of CO and constrain the gas mass in discs that were known to host gas previously, and to search for gas in the remaining 13 discs without previous CO detections. Methods. We developed a line-imaging pipeline for ARKS CO data with a high spectro-spatial resolution. Using this tool, we produced line cubes for each of the ARKS targets, with a spatial resolution down to about 70 mas and a spectral resolution of 26 m s⁻¹. We used spectro-spatial shifting and stacking techniques to produce a gallery of maps with the highest possible signal-to-noise ratio (S/N) and with radial and spectral profiles that reveal the distribution and kinematics of gas in five gas-bearing discs at unprecedented detail. Results. For each of the five gas-bearing discs (HD 9672/49 Ceti, HD 32297, HD 121617, HD 131488, and HD 131835), we constrained the inner radius of the ¹²CO (r_min ~ 3-68 au), and we found that the radial brightness profile of CO peaked interior to the dust ring, but that CO was also more radially extended than the dust. In a second-generation scenario, this would require significant shielding of CO that would allow it to viscously spread to the observed widths. We present the first radially resolved ¹²CO/¹³CO isotopologue flux ratios in five gas-bearing debris discs and found them to be constant with radius for the majority (four out of five) of systems. This indicates that ¹²CO and ¹³CO are both optically thick or optically thin throughout the discs. We report CO line fluxes or upper limits for all systems and optical depth dependant masses for the five systems with detected CO. Finally, we analysed the ¹²CO J=3-2 line luminosities for a range of ARKS debris discs and for debris discs from the literature. We confirm that gas is mostly detected in young systems. However, the high scatter seen in young/high fractional luminosity systems indicates no trend within the systems with detected gas. This could be caused by different system properties and/or evolution pathways.

The ALMA survey to Resolve exoKuiper belt Substructures (ARKS): X. Interpreting the peculiar dust rings around HD 131835

First Author: Jankovic, M. R.
Instruments: ALMA_Band_6, ALMA_Band_7, SPHERE
ProgramIDs: 095.C-0298, 2012.1.00142.S, 2012.1.00198.S, 2015.1.01260.S, 2016.1.00104.S, 2016.1.00195.S, 2016.1.00907.S, 2017.1.00167.S, 2017.1.00825.S, 2018.1.01222.S, 2019.1.00189.S, 2022.1.00338.L
BibCode: 2026A&A...705A.204J

Context. Dusty discs detected around main-sequence stars are thought to be signs of planetesimal belts in which the dust distribution is shaped by collisional and dynamical processes, including interactions with gas if present. The debris disc around the young A-type star HD 131835 is composed of two dust rings at ∼65 au and ∼100 au, a third unconstrained innermost component, and a gaseous component centred at ∼65 au. New ALMA observations show that the inner of the two dust rings is brighter than the outer one, in contrast with previous observations in scattered light. Aims. We explore two scenarios that could explain these observations: the two dust rings might represent distinct planetesimal belts with different collisional properties, or only the inner ring might contain planetesimals while the outer ring consists entirely of dust that has migrated outwards due to gas drag. Methods. To explore the first scenario, we employed a state-of-the-art collisional evolution code. To test the second scenario, we used a simple dynamical model of dust grain evolution in an optically thin gaseous disc. In each case we identified the parameters of the planetesimal and the gaseous disc that best reproduce the observational constraints. Results. Collisional models of two planetesimal belts cannot fully reproduce the observations by only varying their dynamical excitation, and matching the data through a different material strength requires an extreme difference in dust composition. The gas-driven scenario can reproduce the location of the outer ring and the brightness ratio of the two rings from scattered light observations, but the resulting outer ring is too faint overall in both scattered light and sub-millimetre emission. Conclusions. The dust rings in HD 131835 could be produced from two planetesimal belts, although how these belts would attain the required extremely different properties needs to be explained. The dust-gas interaction is a plausible alternative explanation and deserves further study using a more comprehensive model.

The ALMA survey to Resolve exoKuiper belt Substructures (ARKS): IX. Gas-driven origin for the continuum arc in the debris disc of HD121617

First Author: Weber, P.
Instruments: ALMA_Band_6, ALMA_Band_7, SPHERE
ProgramIDs: 0101.C-0420, 2012.1.00142.S, 2012.1.00198.S, 2015.1.01260.S, 2016.1.00104.S, 2016.1.00195.S, 2016.1.00907.S, 2017.1.00167.S, 2017.1.00825.S, 2018.1.01222.S, 2019.1.00189.S, 2022.1.00338.L
BibCode: 2026A&A...705A.203W

Context. Debris discs were long considered to be largely gas-free environments, where dynamical evolution is governed primarily by collisional fragmentation, gravitational stirring, and radiative forces. Recent detections of CO molecular line emission in debris discs demonstrate that gas is present, but its abundance and origin are still uncertain. The ALMA survey to Resolve exoKuiper belt Substructures (ARKS) observed both the gas and dust of several debris discs at high resolution and revealed a narrow ring of gas and dust in the disc HD 121617, with an asymmetric arc-like feature that is 40% brighter than the rest of the ring. Aims. An important open question is how representative the estimated CO masses are for the total gas mass in debris discs. We aim to constrain the total gas mass in HD 121617 using numerical models under the assumption that the dust arc is produced by hydrodynamical processes involving the gas. Methods. We used the hydrodynamical code Dusty FARGO-ADSG, in which dust is modelled as Lagrangian particles. We explored the effects of radiation pressure and dust feedback, as well as of varying the total gas mass on the dynamical evolution of the system. We compared these simulations with observations via radiative transfer calculations. Results. We find that an unstable gas ring can create a size-dependent radial and azimuthal dust trap. The total gas mass dictates the efficiency of particle trapping as a function of grain size. We find that two of our models, M_gas=50 M_⊕ and M_gas=5 M_⊕, can simultaneously reproduce the observed arc in the ALMA band 7 continuum image and the radial outward offset of the VLT/SPHERE scattered light ring, driven by the combined effects of gas drag and radiation pressure. We further find a conservative lower limit of M_gas>2.5 M_⊕ and a conservative upper limit of M_gas<250 M_⊕. Conclusions. If the ALMA band 7 asymmetry is caused by gas drag, reconciling the required gas mass with the observed ¹²CO emission suggests the presence of significant amounts of H₂, consistent with the gas being primordial, that is, long-lived remnant material from the protoplanetary disc phase. In this scenario, HD 121617 would represent a hybrid disc, bridging the protoplanetary and debris disc stages. As an arc-shaped emission can alternatively be reproduced by a planet's gravitational forcing, future observations are crucial to distinguish between these two scenarios.

The ALMA survey to Resolve exoKuiper belt Substructures (ARKS): VII. Optically thick gas with broad CO gaussian local line profiles in the HD 121617 disc

First Author: Brennan, A.
Instruments: ALMA_Band_6, ALMA_Band_7
ProgramIDs: 2012.1.00142.S, 2012.1.00198.S, 2015.1.01260.S, 2016.1.00104.S, 2016.1.00195.S, 2016.1.00907.S, 2017.1.00167.S, 2017.1.00825.S, 2018.1.01222.S, 2019.1.00189.S, 2022.1.00338.L
BibCode: 2026A&A...705A.201B

Context. CO gas has been detected in ~20 debris discs, typically classified as CO-poor or CO-rich. We present observations of the CO-rich HD 121617 debris disc as part of the ALMA survey to Resolve exoKuiper belt Substructures (ARKS). Aims. We model local CO line profiles in the HD 121617 debris disc to investigate optical depth, CO mass, and temperature. HD 121617 is a well-suited ARKS target due to its previously detected CO emission and moderate inclination, reducing the effect of Keplerian shear. Methods. Using high-resolution ALMA Band 7 observations of ¹²CO J=3─2 (26 m s⁻¹, 0_⋅'' 1), we create local line profiles by aligning and stacking spectra in concentric annuli of 0_⋅'' 02 width. These profiles are modelled with both a toy model and a RADMC-3D model that includes projection effects and Keplerian shear. Results. The resulting local profiles are Gaussian-shaped and broad due to the effect of Keplerian shear. Fitting a RADMC-3D model to the ¹³CO data, we find that an optically thick model (temperature of 38 K and mass of 2 × 10⁻³ M_⊕) reproduces the data, particularly the enhanced intensity at orbital azimuths of ~±45° and ±135°, which forms an X-shape in the velocity integrated intensity map, as well as the broader ¹²CO linewidth compared to ¹³CO. Scaling this model by the ISM abundance ratio (~77) also reproduces the ¹²CO data, but high optical depths and model assumptions limit mass constraints. Conclusions. Keplerian shear causes azimuthally averaged line profiles to appear Gaussian regardless of optical depth; therefore, we caution against using the local line profiles to distinguish between optically thin and thick emission. We constrain the mean molecular weight to 12.6_−1.1^+1.3, dependent on model assumptions. Although model dependent, our ¹³CO results indicate that C¹⁸O might also be optically thick in CO-rich debris discs, contrary to previous assumptions, and that the mean molecular weight is significantly higher than if H₂ were the dominant gas species, suggesting a non-primordial composition.

The ALMA survey to Resolve exoKuiper belt Substructures (ARKS): VI. Asymmetries and offsets

First Author: Lovell, J. B.
Instruments: ALMA_Band_6, ALMA_Band_7, SPHERE
ProgramIDs: 096.C-0640, 0104.C-0436, 0102.C-0916, 095.C-0273, 0101.C-0753, 098.C-0686, 095.C-0298, 0101.C-0420, 2012.1.00142.S, 2012.1.00198.S, 2015.1.01260.S, 2016.1.00104.S, 2016.1.00195.S, 2016.1.00907.S, 2017.1.00167.S, 2017.1.00825.S, 2018.1.01222.S, 2019.1.00189.S, 2022.1.00338.L
BibCode: 2026A&A...705A.200L

Context. Asymmetries in debris discs provide unique clues to understand the evolution and architecture of planetary systems. Previous studies of debris discs at (sub)millimetre wavelengths have suggested the presence of asymmetries in a wide variety of systems, yet the lack of sufficiently sensitive high-resolution observations means that the typical properties of debris disc asymmetries have not been studied at the population level. The aim of the ALMA survey to Resolve exoKuiper belt Substructures (ARKS) is to expand our understanding of radial and vertical dust structures, as well as gas distributions and kinematics, in debris discs. The ARKS sample of 24 highly resolved targets in ALMA's Bands 6 and 7 (1.1─1.4 mm and 0.8─1.1 mm, respectively) provided a unique opportunity to study their asymmetries. Aims. Here, in ARKS VI, we present a systematic analysis of the asymmetries and stellocentric offsets present in the ALMA continuum data for the ARKS survey. Our aims are to (i) identify asymmetries in debris disc dust distributions, (ii) quantify debris disc asymmetry properties, and (iii) discuss the potential origins of debris disc asymmetries. This work is the first systematic analysis of asymmetries in a large sample of well-resolved discs at (sub)millimetre wavelengths. Methods. We utilised empirical methods to identify emission asymmetries (relative to disc major and minor axes, and azimuthal disc locations) and the presence of offset emission between disc centres and the locations of the host stars, via an analysis of their calibration procedures and disc properties. We associated observational asymmetry types (offset, major and/or minor axis, azimuthal) and plausible physical classes (arcs, eccentricities, and possible clumps and warps) associated with each source. Results. We show that there are ten systems, almost half of the ARKS sample, that host either a continuum emission asymmetry or offset emission. Three systems host offsets (HD 15115, HD 32297, and HD 109573 (HR 4796)), four host azimuthal asymmetries (HD 9672 (49 Ceti), HD 92945, HD 107146, and HD 121617), two host an asymmetry in their major axis (HD 10647 (q¹ Eri), and HD 39060 (β Pic)), and one hosts an asymmetry in their minor axis (HD 61005). We attribute the offset asymmetries to non-zero eccentricities, and three of the azimuthal asymmetries to arcs. The presence of an asymmetry or offset in the ARKS sample appears to be correlated with the fractional luminosity of cold dust. We tentatively suggest that continuum asymmetries are more prevalent in CO-rich debris discs, suggesting that gas interactions may drive debris dust asymmetries. We identify seven other tentative asymmetries, including four in distinct ARKS systems and three in systems with otherwise significant asymmetries. Conclusions. This study demonstrates that debris disc asymmetries in the ARKS sample are common, and plausibly so in the wider population of debris discs at (sub)-millimetre wavelengths. This means that (sub)-millimetre asymmetries plausibly await discovery in debris discs as we probe these with higher sensitivity and resolution. Throughout, we highlight future studies to further investigate the origins of debris disc asymmetries, and build on the work presented here.

The ALMA survey to Resolve exoKuiper belt Substructures (ARKS): II. The radial structure of debris discs

First Author: Han, Yinuo
Instruments: ALMA_Band_6, ALMA_Band_7
ProgramIDs: 2012.1.00142.S, 2012.1.00198.S, 2015.1.01260.S, 2016.1.00104.S, 2016.1.00195.S, 2016.1.00907.S, 2017.1.00167.S, 2017.1.00825.S, 2018.1.01222.S, 2019.1.00189.S, 2022.1.00338.L
BibCode: 2026A&A...705A.196H

Context. Debris discs are populated by belts of planetesimals, whose structure carries dynamical imprints of planets and the formation and evolutionary history of the planetary system. The relatively faint emission of debris discs has previously made it challenging to obtain a large sample of high-resolution ALMA images to characterise their substructures. Aims. The ALMA survey to Resolve exoKuiper belt Substructures (ARKS) was recently completed to cover the lack of high-resolution observations and to investigate the prevalence of substructures such as radial gaps and rings in a sample of 24 debris discs. This study characterises the radial structure of debris discs in the ARKS programme. Methods. We modelled all discs with a range of non-parametric and parametric approaches, including those that deconvolve and deproject the image or fit the visibilities directly, in order to identify and quantify the disc substructures. Results. Across the sample we find that of the 24 discs, 5 host multiple rings, 7 are single rings that display halos or additional low-amplitude rings, and 12 are single rings with at most tentative evidence of additional substructures. The fractional ring widths that we measured are significantly narrower than previously derived values, and they follow a distribution similar to the fractional widths of individual rings resolved in protoplanetary discs. However, there exists a population of rings in debris discs that are significantly wider than those in protoplanetary discs. We also find that discs with steep inner edges consistent with planet sculpting tend to be found at smaller (<100 au) radii, while more radially extended discs tend to have shallower edges more consistent with collisional evolution. An overwhelming majority of discs have radial profiles that are well-described by either a double power law or double-Gaussian parametrisation. Conclusions. While our findings suggest that it may be possible for some debris discs to inherit their structures directly from pro-toplanetary discs, there exists a sizeable population of broad debris discs that cannot be explained in this way. Assuming that the distribution of millimetre dust reflects the distribution of planetesimals, mechanisms that cause rings in protoplanetary discs to migrate or debris discs to broaden soon after formation may be at play, possibly mediated by planetary migration or scattering.

The ALMA survey to Resolve exoKuiper belt Substructures (ARKS): I. Motivation, sample, data reduction, and results overview

First Author: Marino, S.
Instruments: ALMA_Band_6, ALMA_Band_7
ProgramIDs: 2012.1.00142.S, 2012.1.00198.S, 2015.1.01260.S, 2016.1.00104.S, 2016.1.00195.S, 2016.1.00907.S, 2017.1.00167.S, 2017.1.00825.S, 2018.1.01222.S, 2019.1.00189.S, 2022.1.00338.L
BibCode: 2026A&A...705A.195M

Context. The outer regions of planetary systems host dusty debris discs analogous to the Kuiper belt (exoKuiper belts), which provide crucial constraints on planet formation and evolution processes. ALMA dust observations have revealed a great diversity in terms of radii, widths, and scale heights. At the same time, ALMA has also shown that some belts contain CO gas, whose origin and implications are still highly uncertain. Most of this progress, however, has been limited by low angular resolution observations that hinder our ability to test existing models and theories. Aims. High-resolution observations of these belts are crucial for understanding the detailed distribution of solids and for constraining the gas distribution and kinematics. Methods. We conducted the first ALMA large programme dedicated to debris discs: the ALMA survey to Resolve exoKuiper belt Substructures (ARKS). We selected the 24 most promising belts to best address our main objectives: analysing the detailed radial and vertical structure, and characterising the gas content. The data were reduced and corrected to account for several systematic effects, and then imaged. Using parametric and non-parametric models, we constrained the radial and vertical distribution of dust, as well as the presence of asymmetries. For a subset of six belts with CO gas, we constrained the gas distribution and kinematics. To interpret these observations, we used a wide range of dynamical models. Results. The first results of ARKS are presented as a series of ten papers. We discovered that up to 33% of our sample exhibits substructures in the form of multiple dusty rings that may have been inherited from their protoplanetary discs. For highly inclined belts, we found that non-Gaussian vertical distributions are common and could be indicative of multiple dynamical populations. Half of the derived scale heights are small enough to be consistent with self-stirring in low-mass belts (M_belt ≤ M_Neptune). We also found that 10 of the 24 belts present asymmetries in the form of density enhancements, eccentricities, or warps. We find that the CO gas is radially broader than the dust, but this could be an effect of optical depth. At least one system shows non-Keplerian kinematics due to strong pressure gradients, which may have triggered a vortex that trapped dust in an arc. Finally, we find evidence that the micron-sized grains may be affected by gas drag in gas-rich systems, pushing the small grains to wider orbits than the large grains. Conclusions. ARKS has revealed a great diversity of radial and vertical structures in exoKuiper belts that may arise when they are formed in protoplanetary discs or subsequently via interactions with planets and/or gas. We encourage the community to explore the reduced data and data products that we have made public through a dedicated website.

Stellar-mass black holes on the millimetre Fundamental Plane of black hole accretion

First Author: Elford, Jacob S.
Instruments: ALMA_Band_3, ALMA_Band_6
ProgramIDs: 2016.1.00496.S, 2016.1.00773.S, 2017.1.00051.S, 2019.1.01324.T, 2023.1.00887.S
BibCode: 2026MNRAS.546ag037E

Recent work revealed the existence of a galaxy 'millimetre Fundamental Plane of black hole accretion', a tight correlation between nuclear 1 mm luminosity, intrinsic 2─10 keV X-ray luminosity and supermassive black hole mass, originally discovered for nearby low- and high-luminosity active galactic nuclei. Here we use mm and X-ray data of five X-ray binaries (XRBs) to demonstrate that these stellar-mass black holes also lie on the mm Fundamental Plane, as they do at radio wavelengths. One source for which we have multi-epoch observations shows evidence of deviations from the plane after a state change, suggesting that the plane only applies to XRBs in the hard state, as is true again at radio wavelengths. We show that both advection-dominated accretion flows and compact jet models predict the existence of the plane across the entire range of black hole masses, although these models vary in their ability to accurately predict the XRB black hole masses.

On the multiplicity of red-Herschel sources and its implications for extreme star formation

First Author: Quirós-Rojas, Marianela
Instruments: ALMA_Band_6, ALMA_Band_7
ProgramIDs: 2016.1.00087.S, 2016.1.00139.S, 2017.1.00510.S, 2018.1.00489.S, 2018.1.00526.S, 2021.1.01628.S, 2022.1.00432.S
BibCode: 2026MNRAS.545f2133Q

We study the multiplicity of galaxies in the largest sample of red-Herschel sources (

$S_{250 \, \mu \mathrm{m}} < S_{350 \, \mu \mathrm{m}} < S_{500 \, \mu \mathrm{m}}$

) using archival Atacama Large Millimeter/submillimeter Array (ALMA) observations. Out of 2416 fields with ALMA detections (from a total of 3089 analysed maps), we identify 474 multiple systems within a radius of 16 arcsec (equivalent to the 500

$\mu$

m Herschel beam size): 420 doubles, 51 triples, and 3 quadruples. In each case, the brightest source contributes, on average, 64, 48, and 42 per cent of the total flux in double, triple, and quadruple systems. The average combined ALMA flux density of the sources in double systems is comparable to that of the two brightest components within triple and quadruple systems. Non-parametric tests suggest that only a small fraction of the double systems (

${\lesssim} 13$

per cent) are composed of sources with compatible redshifts, while 47─67 per cent of triple and quadruple fields contain at least one potentially associated pair. Simulations using a mock catalogue of dusty star-forming galaxies suggest that 32 per cent of the double systems are likely physically associated (

$\Delta z < 0.01$

, i.e.

$\lesssim$

10 cMpc at

$z = 3$

) and, while only 8 per cent of the triple and none of the quadruple systems meet this criterion,

${\sim}$

70 per cent of them include at least one likely associated pair. Our results suggest that enhanced star formation rates in submillimetre galaxies are primarily driven by internal processes rather than large-scale interactions. This study also provides a catalogue of potential overdensities for follow-up observations, offering insights into protocluster formation and evolution.

Ring Asymmetry and Spin in M87*

First Author: Bernshteyn, Vadim
Instruments: ALMA_Band_6
ProgramIDs: 2017.1.00841.V, 2019.1.01797.V
BibCode: 2026ApJ..1000..231B

Event Horizon Telescope (EHT) images of the supermassive black hole M87* depict an asymmetric ring of emission. General relativistic magnetohydrodynamic (GRMHD) models of M87* and its accretion disk predict that the amplitude and location of the ring's peak brightness asymmetry should fluctuate due to turbulence in the source plasma. We compare the observed distribution of brightness asymmetry amplitudes to the simulated distribution in GRMHD models, across varying black hole spin a_*. We show that, for strongly magnetized (MAD) models, three epochs of EHT data marginally disfavor ∣a_*∣ ≲ 0.2. This is consistent with the Blandford─Znajek model for M87's jet, which predicts that M87* should have nonzero spin. We show quantitatively how future observations could improve spin constraints and discuss how improved spin constraints could distinguish between differing jet-launching mechanisms and black hole growth scenarios.

Unveiling the collision between molecular outflows: observational evidence and hydrodynamic simulations

First Author: Cohen-Arazi, E.
Instruments: ALMA_Band_7
ProgramIDs: 2017.1.00914.S
BibCode: 2026MNRAS.547ag071C

We present an unexplored scenario for interpreting the outflows in the EGO G338.92+0.55 (b) region (hereafter, EGO G338). Within this framework, we investigate the hypothesis that the interaction between two outflows is responsible for the observed morphology and kinematics of this astrophysical object. To explore this possibility, we reanalyse the region using observational molecular line data. We base our analysis on maps of moments 0, 1, and 2 of the CO emission associated with the molecular outflows. Additionally, we conduct three-dimensional hydrodynamic simulations to examine the presence or absence of a collision between two jets. From our numerical results, we produce synthetic CO images to facilitate a direct comparison with observations. The findings of this study provide compelling evidence that the observed morphology and kinematics in the EGO G338 region are the result of a likely collision between two molecular outflows.

ALMA Band 9 CO(6─5) Reveals a Warm Ring Structure Associated with the Embedded Protostar in the Cold Dense Core MC 27/L1521F

First Author: Tokuda, Kazuki
Instruments: ALMA_Band_6, ALMA_Band_7, ALMA_Band_9
ProgramIDs: 2011.0.00611.S, 2015.1.00340.S, 2024.1.00023.S
BibCode: 2026ApJ..1001L...1T

Infall and outflows, coupled with magnetic fields, rapidly structure the gas around newborn protostars. Shocks from interacting components encode the temperature and density distribution, offering a direct probe of the earliest evolution history. However, interferometric observations characterizing warm envelopes using high-excitation lines remain scarce. We present Atacama Large Millimeter/submillimeter Array Band 9 observations of the Taurus dense core MC 27/L1521F, which hosts a Class 0 protostar, targeting the CO(J = 6─5) line at an angular resolution of ∼2″ (≍300 au). We detect an off-centered ringlike structure with a diameter of ∼1000 au that was not identifiable in previous low-J CO data, where emission close to the systemic velocity is strongly affected by optical depth. The ring shows a typical peak brightness temperature of ∼3 K at our resolution. Excitation considerations indicate that the detected CO(J = 6─5) emission likely arises from relatively warm (T ≳ 20 K) and dense (n(H₂) ≳ 10⁵ cm⁻³) gas embedded within the surrounding cold, dense core. The morphology and kinematics suggest an energetic and localized shock-heating event, potentially linked to dynamical gas─magnetic-field interactions in the earliest protostellar phase. Our results demonstrate that high-J CO observations provide a powerful new window on warm and dense gas components, enabling a more direct view of the physical processes operating at the onset of star formation.

Disk Wind Feedback from High-mass Protostars. V. Application of Multimodal Machine Learning to Characterize Outflow Properties

First Author: Xu, Duo
Instruments: ALMA_Band_6
ProgramIDs: 2015.1.01454.S
BibCode: 2026ApJ..1001..120X

Characterizing protostellar outflows is fundamental to understanding star formation feedback, yet traditional methods are often hindered by projection effects and complex morphologies. We present a multimodal deep learning framework that jointly leverages spatial and spectral information from CO observations to infer protostellar mass, inclination, and position angle (PA). Our model, trained on synthetic Atacama Large Millimeter/submillimeter Array (ALMA) observations generated from 3D magnetohydrodynamic simulations, utilizes a cross-attention fusion mechanism to integrate morphological and kinematic features with probabilistic uncertainty estimation. Our results demonstrate that Vision Transformer architectures significantly outperform convolutional networks, showing remarkable robustness to reduced spatial resolution. Interpretability analysis reveals a physically consistent hierarchy: spatial features dominate across all parameters, whereas spectral profiles provide secondary constraints for mass and inclination. Applied to observational ALMA data, the framework delivers stable mass and PA estimates with exceptionally tightly constrained inclination angles. This study establishes multimodal deep learning as a powerful, interpretable tool for overcoming projection biases in high-mass star formation studies.

Full-polarization millimeter wavelength variability of Sagittarius A^* during the 2018 EHT campaign

First Author: Albentosa-Ruiz, Ezequiel
Instruments: ALMA_Band_6
ProgramIDs: 2017.1.00797.V
BibCode: 2026A&A...708A.179A

Context. Sagittarius A* (Sgr A^*), the supermassive black hole at the center of the Milky Way, provides a unique laboratory to study accretion dynamics and plasma processes near the event horizon. Aims. We investigated the variability and polarization properties of Sgr A^* using ALMA observations during the 2018 Event Horizon Telescope campaign. Methods. We analyzed high-cadence full-polarization light curves from ALMA at millimeter wavelengths, performed time-series analysis, and investigated the temporal behavior during an X-ray flare observed by Chandra on 2018 April 24. The variability characteristics are compared with expectations from standard accretion flow models. Results. We find low variability in total intensity (σ/μ < 10%), but significantly higher variability in linear and circular polarization (∼30% and ∼50%, respectively). A time-series analysis reveals red-noise variability, with power spectral densities between −2 and −3 across all Stokes parameters. Polarized intensity shows stable intra-day timescales, while total intensity exhibits more variable timescales, suggesting distinct emission regions, with polarization likely arising from a coherent structure. On April 24, a statistically significant inter-band delay in polarized intensity coincides with a near-simultaneous X-ray and millimeter peak that deviates from the typical delayed flare scenario. This event also features enhanced millimeter variability and coherent polarization loop evolution. The observed simultaneity challenges standard models of transient synchrotron emission with cooling delays, favoring instead a scenario of continuous energy injection in an optically thin region. Conclusions. Our results offer new constraints on the physical mechanisms driving variability in Sgr A^*, and provide key observational input for refining theoretical models of accretion and plasma behavior in the vicinity of supermassive black holes.

Warps survive beyond fly-by encounters in protoplanetary disks: RW Aur A as a case study

First Author: Kimmig, C. N.
Instruments: ALMA_Band_6
ProgramIDs: 2018.1.00973.S
BibCode: 2026A&A...708A.194K

Aims. Stellar fly-bys can have multiple dynamical effects on protoplanetary disks, including warping and the excitation of spiral arms. Since observations indicate that warps are common, we aim to investigate these effects for different fly-by trajectories. We further link our models to observations by applying them to the RW Aur system, which is a fly-by candidate with a well-constrained trajectory. Methods. We investigated the disk dynamics in grid-based hydrodynamical simulations, which allow for a lower disk viscosity than in commonly used smoothed particle hydrodynamics models. We post-processed our simulations of the RW Aur system with radiative transfer models to create synthetic images of the dust continuum and gas kinematics. Results. Fly-bys inclined with respect to the original disk plane can excite warps of a few degrees, but the exact outcome depends on the specific geometry of the encounter. Specifically, we find that the position of the periastron with respect to the initial disk plane plays a role in the resulting warp strength. Within our parameter set, the strongest warp is excited for a retrograde fly-by with a periastron that is not in the same plane as the disk. Our models show that the warp can persist even after the perturber can no longer be clearly linked to the system, implying that past fly-bys are a possible origin of observed warps. Excited spirals arms, on the other hand, are much more short-lived than a warp. We performed a simulation of the recent close encounter in the observed disk around RW Aur A, one of the few systems with a well-constrained trajectory. We find that a warp of about 5° can be excited and that the strong spiral arms have already disappeared at the current time of observation (300 yr after periastron). This compares well with existing continuum observations, and our synthetic kinematic evaluations hint at remnant structures in the gas density that may be detectable.

Multiwavelength ALMA Imaging of HD 34282: Dust-trapping Signatures of a Vortex Candidate

First Author: Ma, Xiaoyi
Instruments: ALMA_Band_3, ALMA_Band_4, ALMA_Band_6, ALMA_Band_7
ProgramIDs: 2022.1.00315.S, 2015.1.00192.S, 2017.1.01578.S, 2023.1.00108.S
BibCode: 2026ApJ..1001..124M

Azimuthal arcs in millimeter continuum emission from protoplanetary disks are often attributed to dust-trapping vortices, but definitive observational confirmation of vortices remains lacking. We present sub- 0.″1 resolution Atacama Large Millimeter/submillimeter Array continuum observations of the HD 34282 disk at 0.9, 1.3, 2.1, and 3.1 mm. These observations resolve a bright azimuthal arc superposed on a compact double-gap, triple-ring morphology, most clearly at shorter wavelengths, and enable us to probe the physical origin of the arc. It exhibits a lower spectral index than the surrounding rings, consistent with enhanced grain growth and/or higher dust surface density of a dust-trapping vortex. Its azimuthal width decreases with increasing wavelength, consistent with tighter confinement of larger grains or lower optical depths at longer wavelengths. These observations probe dust with Stokes numbers St ≲ 0.03. Vortex models predict negligible peak shifts in this regime, consistent with the 1.3─3.1 mm data. At 0.9 mm; however, the arc peak is offset by ∼15^∘ ± 4^∘ in the direction of disk rotation relative to longer wavelengths, and the nearside ring emission is locally dimmer compared to the farside, likely reflecting optical-depth or temperature effects. These observations are consistent with azimuthal dust trapping, potentially associated with a vortex-induced pressure maximum.

astromorph: self-supervised machine learning pipeline for astronomical morphology analysis

First Author: Bjerkeli, P.
Instruments: ALMA_Band_6
ProgramIDs: 2018.1.00532.S
BibCode: 2026A&A...708A.156B

Context. Modern telescopes generate increasingly large and diverse datasets, often consisting of complex and morphologically rich structures. To efficiently explore such data requires automated methods that can extract and organize physically meaningful information, ideally without the need for extensive manual interaction. Aims. Our aim is to provide a user-friendly implementation of a self-supervised machine learning framework to explore morphological properties of large datasets, based on the Bootstrap Your Own Latents (BYOL) method. By enabling the generation of meaningful image embeddings without manually labelled data, the framework will enable key tasks such as clustering, anomaly detection, and similarity-based exploration. Methods. We present astromorph, a Python package that implements the BYOL method in a way tailored for astronomical imaging. In contrast to existing BYOL implementations, astromorph accommodates data of varying dimensions and resolutions, including both single-channel FITS images and multi-channel spectral cubes. The package is built with usability in mind, and offers streamlined pipeline scripts for ease of use as well as deeper customization options via PyTorch-based classes. Results. To demonstrate the utility of astromorph, we apply it in two contrasting science cases representing different astronomical domains: images of protoplanetary disks observed with the Atacama Large Millimeter/submillimeter Array (ALMA), and infrared dark clouds observed with Spitzer and Herschel. In both cases we demonstrate how astromorph produces scientifically meaningful embeddings that capture morphological differences and similarities across large samples. Conclusions. astromorph enables users to apply a robust, label-free approach for uncovering morphological patterns in astronomical datasets. The successful application to two markedly different datasets suggests that the pipeline is broadly applicable across a wide range of imaging-rich astronomical contexts, providing a user-friendly tool for advancing discovery in observational astronomy.

JOYS: JWST MIRI/MRS spectra of the inner 500 au region of the L1527 IRS bipolar outflow

First Author: Devaraj, R.
Instruments: ALMA_Band_6
ProgramIDs: 2019.1.00261.L, 2019.A.00034.S
BibCode: 2026A&A...708A..29D

Context. Outflows and jets are defining characteristics in protostellar evolution, intimately linked to accretion. Understanding their properties and origins is essential for probing the earliest phases of star formation. Aims. This study characterizes the physical and kinematic properties within the innermost 500 au region of the L1527 bipolar outflow, a class 0/I low-mass protostar, as part of the JWST Observations of Young protoStars (JOYS) program. Methods. We obtained spectroscopic observations using the JWST MIRI/MRS instrument across 5-28 μm at 0.2-1.0″ spatial resolution. We identified emission lines from molecular and ionized species and analyzed their spatial morphology using line-integrated intensity maps. We derived gas temperatures and column densities from excitation diagram analysis of H₂ rotational lines and compared results with shock models. Results. The observations reveal extended molecular hydrogen emission tracing the bipolar outflow, with the H₂ gas temperatures distributed into warm (~550 K) and hot (~2500 K) components, likely originating from moderate-velocity J -type shocks and some UV irradiation. We detect forbidden atomic and ionized emission lines of [Ni II], [Ar II], [Ne II], [Ne III], [S I], and [Fe II] showing spatially extended morphology. Double-peaked emission profiles were seen in [Ar II], [Ne III], and [Fe II] in the eastern region, suggesting that the high-velocity component traces a fast, highly ionized jet. A radial velocity map derived from [Ne II] emission shows the eastern region to be redshifted and the western region blueshifted, contrary to earlier interpretations. Conclusions. The analysis of the MIRI/MRS observations reveals molecular, atomic, and ionized emission lines in this low-mass protostar connected with active outflow signatures. The most striking feature discovered is a poorly collimated high-velocity ionized jet, embedded within a broader, wide-angle molecular outflow likely driven by a disk wind. The coexistence of these components supports a stratified outflow structure and suggests that L1527 exhibits jet-launching characteristics atypical of its early evolutionary stage.

Diverse stages of star formation in the IRAS 18162-2048 region: Emergence of UV feedback

First Author: Fedriani, R.
Instruments: ALMA_Band_3, SINFONI
ProgramIDs: 0101.C-0317, 2012.1.00441.S
BibCode: 2026A&A...708A..11F

Context. High-mass star formation remains a major open problem in astrophysics, particularly regarding the transition between deeply embedded protostars and the onset of ionising radiation capable of producing photodissociation regions (PDRs) and compact H II regions. Aims. We aim to characterise the excitation and ionisation conditions of the high-mass star-forming region IRAS 18162−2048, which is where the parsec-scale jet HH80−81 lies. Methods. We obtained adaptive optics─assisted integral field spectroscopy in the near-IR K band (1.93─2.47 µm) with VLT/SINFONI, complemented by VLA X and C bands (3−6 cm) and ALMA band 3 (∼3.3 mm) observations. We analysed the continuum and line emission to derive visual extinction and excitation conditions and the kinematics of the gas of the region. Results. The near-IR continuum reveals two IR sources, IRS 2 and IRS 7, while the main protostellar core, IRAS 18162-2048, remains undetected up to 2.47 µm. IRS 7 shows a peculiar hydrogen recombination line (HRL) Brγ profile with a narrow emission component superimposed on a broad absorption feature, consistent with a B2/B3 zero-age main-sequence (ZAMS) star. Extended H₂ emission exhibits a 'sawtooth' pattern in the excitation diagram, characteristic of UV radiation in a PDR rather than shock excitation. The radiative transfer model Cloudy reproduces the H₂ ro-vibrational populations for T_gas = 600 K and n_H = 7.9 × 10³ cm⁻³. The VLA X and C bands observations reveal a compact radio source previously reported as a 'stationary condensation' (SC) and coincident with IRS 7. For the first time, we detect IRS 7/SC in millimetre wavelengths. The spectral index in the 3−6 cm and 3.3 mm regime is consistent with optically thin free─free emission. Conclusions. Our near-IR and radio observations reveal that IRS 7/SC is a B2/B3 ZAMS star that has begun to photo-ionise its environment, giving rise to an extended PDR and a compact H II region. The coexistence of this source with the deeply embedded protostar IRAS 18162-2048 and other bubble-like structures in the field suggests a multi-generational star-forming environment. Future James Webb Space Telescope observations targeting the H₂ pure rotational lines (3─28 µm) and other HRLs less affected by extinction will be essential to characterising the cooler molecular and ionised gas to fully disclose the formation history of the region.

MUSE-ALMA Haloes: XIV. The ALMA Large Programme Data Release

First Author: Péroux, Céline
Instruments: ALMA_Band_4, ALMA_Band_6, UVES
ProgramIDs: 113.2693, 2023.1.00127.L
BibCode: 2026A&A...708A.146P

The interactions between gas and galaxies are of paramount importance to our understanding of structure formation. A fundamental element of such baryon cycle studies is a complete census of the condensed matter (stars and cold gas) in both galaxies and their immediate surroundings, the so-called circumgalactic medium. Of particular importance are the processes of converting molecular gas into stars and deciphering whether this < 100 K gas is tracing gas flows. The MUSE-ALMA Haloes survey assembled probes of the neutral atomic gas H I, ionised gas, and stellar component for a sample of 79 z ∼ 0.5 galaxies. This was achieved by combining absorption-line spectroscopy of background quasars with a projected impact parameter as low as 5 kpc and as high as 250 kpc to probe the low-density circumgalactic gas with emission-line tracers of both ionised gas and stars. This paper presents the Large Programme observational setup and releases the data characterising the molecular phase of some of the MUSE-ALMA Haloes targets so as to reach a complete census of their condensed baryons. ALMA's unique millimetre coverage and high sensitivity are ideal for characterising the CO emission of these z ∼ 0.5 H I-selected galaxies. By measuring the molecular mass, kinematics, gas flows, and gas fractions, this project (i) quantifies the role of molecular gas in H I-rich galaxies, (ii) characterises the molecular phase of gas flows from morpho-kinematics analyses, and (iii) establishes a census of the condensed baryons in the interstellar and circumgalactic media. Ultimately, these results will provide unique insights into the baryon cycle ─ a crucial component of galaxy formation.

The ALPINE-CRISTAL-JWST Survey: Chemical Abundance Comparison between the ISM and CGM of Main-sequence Galaxies at z = 4─6

First Author: Wang, Wuji
Instruments: ALMA_Band_7
ProgramIDs: 2017.1.00428.L, 2019.1.00226.S, 2022.1.01118.S, 2021.1.00280.L
BibCode: 2026ApJ..1000..308W

Gaseous halos around galaxies play an important role in galaxy evolution. The exchange of metals from the interstellar medium (ISM) to the circumgalactic medium (CGM) is caused by the formation, feedback, and/or merging history of galaxies. We study the variation in chemical composition between the ISM (≲3 kpc) and CGM (∼5─10 kpc) for a sample of M_⋆ > 10^9.5 M_⊙ main-sequence galaxies at 4 < z < 6 with both JWST and Atacama Large Millimeter/submillimeter Array observations. Using JWST/NIRSpec integral field spectroscopy, we derive the optical line ratios from the ISM and the CGM for our sample, focusing on the typical optical lines used for metallicity studies. Our comparison shows that the ISM and the CGM have similar chemical abundances. This indicates that the CGM of these typical 4 < z < 6 galaxies is enriched to the level of their ISM in the early Universe. Using statistical tests, we find that some of the line ratios show marginal differences between the ISM and CGM. Combined with Cloudy modeling, our results suggest that a difference in ionization level (higher for the ISM) is the dominant reason for the observed ratio difference of oxygen line ratios. There is also indication of a deficit in the nitrogen abundance with respect to oxygen in the CGM, which suggests a delay in redistribution of secondary nitrogen. Finally, an enhanced F_{[C II]158μm}/F_Hα ratio is observed in the CGM, suggesting that feedback and/or mergers play a key role in metal mixing.

A Potential Link between Nuclear Winds and Cold Gas Outflows on Kiloparsec Scales in Reionization-era Quasars

First Author: Zhu, Yongda
Instruments: ALMA_Band_7
ProgramIDs: 2022.1.00662.S
BibCode: 2026ApJ..1000..312Z

Feedback from accreting supermassive black holes may regulate galaxy evolution, but statistical evidence linking nuclear winds to kiloparsec-scale cold gas outflows remains limited in the early Universe. Here, we report statistical evidence for such a connection in a sample of luminous quasars at z ∼ 5.5. We compare stacked [C II] 158 μm emission profiles from Atacama Large Millimeter/submillimeter Array observations, which trace galactic-scale neutral gas, for quasars with and without broad absorption lines (BALs) that indicate powerful nuclear winds on subkiloparsec scales. A total of 5 BAL and 11 non-BAL quasar spectra are included in the stacking analysis. The BAL quasar stack exhibits a potential blueshifted broad component in the [C II] line profile, with a velocity offset of ∆v_b = −2.1 × 10² km s⁻¹ and a full width at half-maximum of 1.18 × 10³ km s⁻¹, whereas the non-BAL stack shows no obvious broad component. Using a conservative "clean-stack" selection that excludes quasars with partial [C II] spectral coverage, the BAL broad residual is reduced to a hint-level feature. We estimate that up to a few percent to one quarter of the nuclear wind energy may be transferred to cold neutral gas on kiloparsec scales. Although the sample size is limited, these results suggest a potential link between BAL winds and cold gas feedback in quasar host galaxies. These results provide empirical motivation for future tests of how multiphase outflows relate to the diversity of quasar host properties, including M_BH/M_*.

Substellar initial mass function of Trumpler 14

First Author: Rom, T.
Instruments: VIRCAM
ProgramIDs: 088.C-0117
BibCode: 2026A&A...706A..58R

Context. Young, massive stellar clusters offer a prime setting to explore brown dwarf (BD) formation under high densities and intense UV radiation. Trumpler 14 (Tr 14), a ∼1 Myr old cluster located at a distance of 2.4 kpc that is particularly rich in O-type stars, is an ideal target for such a study. Aims. Our goal is to measure the initial mass function (IMF) in the young massive, high-UV-flux cluster. Methods. We present the deepest study to date of the IMF in Tr 14, based on Gemini Multi-Conjugate Adaptive Optics System/Gemini-South Adaptive Optics Imager imaging. We constructed the IMF using both the Besançon Galactic model and an observational control field from VISTA for background correction. Completeness was assessed using artificial star tests and applied to the IMF derivation. Results. We estimated the IMF down to the 20% completeness limit found at ∼0.01 M_⊙. Using the control-field-based IMF as our primary result, we find a slope of α = 0.14 ± 0.19 for masses between 0.01 and 0.2 M_⊙, and α = 1.72 ± 0.04 for 0.2─4.5 M_⊙, where dN/dM ∝ M^−α. The low-mass slope is largely influenced by the incompleteness-affected lowest bin; excluding it brings our results into agreement with those for other young clusters. The resulting median for the star-to-BD ratio in the 0.03─1 M_⊙ mass range is 4.0, with a 95% confidence interval of 2.8─5.8. Conclusions. Our analysis reveals that Tr 14 hosts a relatively flat substellar IMF, but this is strongly influenced by the lowest-mass bin, which may be affected by incompleteness. When that bin is excluded, the IMF becomes consistent with those of other regions. The star-to-BD ratio falls within the usually observed ∼3─6 range, indicating that BDs with masses above ∼0.03 M_⊙ form with similar efficiencies across environments. However, the relative lack of objects below this threshold suggests that the presence of an environment with both high stellar density and far-UV flux plays a role in shaping the IMF by suppressing the formation of BDs at masses <0.03 M_⊙.

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