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Physics Astrophysics Astrophysics of Galaxies

astro-ph.GA Watch Astrophysics of Galaxies

Tuesday 22 September

Astrophysics of Galaxies

Misaligned tidal tails in open clusters: a signature of the local spiral arm resonance

Andrés E. Piatti

Tidal tails of open clusters are traditionally expected to align with their orbital motion due to Galactic shear. However, recent observations suggest that a significant population of clusters exhibits misaligned tails, the origin of which remains poorly understood. I investigate the structural properties of tidal tails for a sample of 155 nearby open clusters within 1 kpc of the Sun to characterize the influence of non-axisymmetric Galactic perturbers on stellar stripping geometry.Using high-precision Gaia DR3 astrometry and the probabilistic membership, I trace the primary orientation and physical length of tidal tails. I distinguish between local and global perturbations by analyzing the spatial distribution of misalignment (DeltaPA) relative to the boundaries of the Local Arm and comparing results with recent test-particle simulations of barred and spiral potentials. I identify three distinct dynamical regimes. While the majority of the population is shear-aligned, a significant subset exhibits a spatially indifferent background misalignment (10deg < DeltaPA < 30deg) consistent with global Galactic bar torques. In contrast, a population of nascent tails (< 0.3 kpc) exhibits larger misalignments (DeltaPA > 40deg) with a unique spatial specificity, occurring exclusively within the inter-arm gaps (|d_arm| > 0.2 kpc). These significant misalignments could represent a transient dynamical phase occurring within the corotation resonance's zero-shear zone, where the radial gravitational forcing of the spiral potential dominates stellar exit trajectories by rotating the eigenvectors of the tidal tensor. This could identify nascent tidal tails as uniquely sensitive high-resolution tracers of the non-axisymmetric Galactic potential.
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Astrophysics of Galaxies

Exploring the influence of reionisation-era galaxies on their local intergalactic medium using the Sherwood-Relics simulations

Hamish Anderson, Laura C. Keating, Luke Conaboy et al. (+3 more)

Recent surveys have detected excess flux in the Lyman-$\alpha$ forest of quasar spectra several Mpc from high-redshift line-emitting galaxies, indicating a correlation between intergalactic medium (IGM) transmission and reionisation-era galaxies. We examine the galaxy-IGM connection using the Sherwood-Relics simulation suite, a set of hybrid radiation-hydrodynamic simulations that model the IGM at high redshift. We simulate the Lyman-$\alpha$ forest and a population of mock [OIII] emitters using the survey specifications of JWST's ASPIRE programme. We measure the evolution of the effective optical depth in regions close to galaxies, and contrast this with a control sample probing the random IGM. We characterise the changing physical properties of the IGM to explain the observed sightline-to-sightline scatter in opacity between 5.4 < $z$ < 6.2. We find that the IGM is more opaque than average at small radii ($r$ $\leq$ 5 cMpc/$h$) close to galaxies, as these regions are overdense. At larger radii (15 < $r$ $\leq$ 50 cMpc/$h$), the IGM is more ionised than average, due to the higher photoionisation rate near galaxies. We find qualitative agreement with the observational results from ASPIRE, though we see large realisation-to-realisation scatter driven by cosmic variance, as also seen in theoretical explorations of the galaxy-Ly$\alpha$ transmission cross-correlation function. Our results generally agree with observations claiming that there is a large-scale ionisation bias around [OIII] emitters, supporting the idea that their role is significant in shaping the properties of the IGM during reionisation.
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All authors Hamish Anderson, Laura C. Keating, Luke Conaboy, Xiangyu Jin, James S. Bolton, Ewald Puchwein

Astrophysics of Galaxies · Cross-listed from astro-ph.CO

Bayesian Galaxy Asymmetry

Mathieu Perron-Cormier, Kristine Spekkens, Nathan Deg et al. (+2 more)

Galaxy asymmetry is an efficient way to characterize galaxy morphology in atomic hydrogen 21 cm emission detections. We propose a novel Bayesian approach to calculate the probability of an underlying squared differences asymmetry in a noisy detection. This approach has a number of advantages, including the recovery of low asymmetry values where prior noise corrections failed. More importantly, our approach provides robust uncertainties on the asymmetry, enabling a wide variety of statistical studies of galaxy populations. This method is generalized for convolved noise measures. We validate our method using a convergence test. Finally, we show how, when applied to the untargeted HI survey WALLABY, our method nearly triples the number of reliable measurements relatively to the previous state-of-the-art technique. This Bayesian approach to measure asymmetry will therefore further unlock the statistical power of widefield galaxy surveys.
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All authors Mathieu Perron-Cormier, Kristine Spekkens, Nathan Deg, Lawrence M. Widrow, Marcin Glowacki

Astrophysics of Galaxies · Cross-listed from astro-ph.EP

NGTS clusters survey - VII. An Enigmatic Short-Period Circumsecondary Disk Candidate in Orion

Niamh Mallaghan, Ernst J. W. de Mooij, Christopher A. Watson et al. (+31 more)

Young stellar systems provide key insights into the processes governing star/planet formation, often exhibiting complex and evolving photometric variability. In this paper, we present an analysis of the object around NOI 105872, observed by the Next Generation Transit Survey (NGTS) to eclipse a young ($4.1\pm0.4$ Myr) M-type star in the Orion Nebula Cluster. The system displays deep, asymmetric eclipses with a period of $\sim0.69$ days, alongside variability in morphology. We combine photometric observations spanning approximately a decade from multiple ground- and space-based facilities to investigate the nature of this system. We explore a range of physical scenarios to reproduce the eclipse profiles and their evolution. After analysis, our preferred explanation is a circumsecondary disk surrounding a companion in orbit around the M-type primary. We adopt a six-parameter disk model and fit the eclipse profiles independently to each dataset. The best-fitting solution yields a disk radius of $\sim 0.005 \mathrm{au}$ or $0.98 R_{*}$, with broadly consistent orientations across epochs, but with variations that may be attributed to disk precession or intrinsic stellar variability. Constraints from the Hill radius imply a companion mass consistent with a very low-mass stellar companion. These results establish NOI 105872 as a candidate for a circumsecondary disk system in a young stellar environment. Continued photometric monitoring and spectroscopic follow-up will be essential to confirm this interpretation. If confirmed, systems such as NOI 105872 provide valuable benchmarks for understanding disk dynamics, companion formation, and the origin of complex eclipse phenomena in young stars.
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All authors Niamh Mallaghan, Ernst J. W. de Mooij, Christopher A. Watson, Edward Gillen, Matthew Kenworthy, Louise D. Nielsen, David R. Anderson, Matthew P. Battley, Edward M. Bryant, Matthew R. Burleigh, Benjamin M. J. Cadell, Sarah L. Casewell, Alexander Chaushev, V. S. Dhillon, Elsa Ducrot, Jorge Fernandez Fernandez, Samuel Gill, Michael Gillon, Michael R. Goad, Faith Hawthorn, Katlyn L. Hobbs, James McCormac, Maximiliano Moyano, Catriona A. Murray, Toby Rodel, Suman Saha, Ramotholo R. Sefako, John Southworth, Mathilde Timmermans, Amaury H. M. J. Triaud, Jose Vines, Richard G. West, Peter J. Wheatley, Tafadzwa Zivave

Astrophysics of Galaxies

Rest-Frame UV and Optical Structural Evolution of Narrowband-Selected Lyman-alpha Emitters at z = 2-7 with JWST/NIRCam

Ronaldo Laishram, Haruka Kusakabe, Satoshi Kikuta et al. (+8 more)

We present a systematic study of the rest-frame ultraviolet (UV) and optical morphologies of Ly$\alpha$ emitters (LAEs) at $z \simeq 2$-$7$ from the SILVERRUSH multi-narrowband catalog, using JWST/NIRCam imaging from COSMOS-Web. We fit Sérsic profiles in four NIRCam filters (F115W, F150W, F277W, F444W) for LAEs spanning $\sim 2.2$ Gyr of cosmic time. LAE sizes show a mild increase from rest-frame UV to optical wavelengths, with a median optical-to-UV size ratio of $R_{e,\rm opt}/R_{e,\rm UV} = 1.14^{+0.01}_{-0.02}$, indicating a small morphological $K$-correction; this offset is significant at $z \leq 5.7$ but not at $z = 6.6$. The rest-frame optical sizes follow a power-law evolution, given by $R_e \propto (1+z)^{-0.94 \pm 0.09}$, decreasing from $0.91^{+0.07}_{-0.07}$ kpc at $z = 2.2$ to $\sim 0.5$ kpc at $z \gtrsim 5$, in close agreement with a recent JWST study of spectroscopically confirmed LAEs. The rest-frame optical size-mass relation slopes are broadly consistent with those of the general star-forming galaxy (SFG) population, while LAEs lie below it in normalization over $z \sim 3$-$6$. More compact LAEs tend to exhibit higher Ly$\alpha$ equivalent widths, a trend driven mainly by the most compact, marginally resolved sources. These compact systems also occupy elevated SFR surface-density regimes, consistent with a scenario in which concentrated star formation may facilitate Ly$\alpha$ escape. No significant correlation of LAE rest-frame optical size with projected large-scale environment is found over $z \simeq 2$-$7$, suggesting that LAE morphology may be governed primarily by internal galaxy properties, except possibly in the most extreme overdensities.
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All authors Ronaldo Laishram, Haruka Kusakabe, Satoshi Kikuta, Shunta Shimizu, Yusei Koyama, Tadayuki Kodama, Michaela Hirschmann, Greta Toni, Carter Flayhart, Rasha M. Samir, Novan Saputra Haryana

Astrophysics of Galaxies

Mass Distribution of M31 from its Rotation Curve up to 167 kpc

Hao Wu, Yang Huang, Huawei Zhang et al. (+2 more)

The mass distribution of the Andromeda galaxy (M31) is fundamental for understanding its dark matter content, assembly history, and dynamical role within the Local Group. However, estimates of M31's total mass remain quite uncertain, partly because of limited dynamical constraints at large galactocentric radii. Moreover, M31's recent merger history has produced abundant tidal substructures and may have left its outer halo out of dynamical equilibrium, complicating equilibrium-based mass estimates. We use over 8,500 tracers with line-of-sight velocities to constrain the rotation curve (RC) of M31 over R=2–167 kpc. In the disk, we derive the RC from a clean tracer sample using the Jeans equation and find good agreement with previous H I measurements. In the halo, we use Gaussian mixture modeling to account for tidal substructures and Galactic foreground contamination and constrain the kinematics of the residual dynamically hot halo. Assuming this halo population can be treated as an equilibrium tracer, we infer the outer RC and constrain M31's mass distribution for different velocity anisotropies beta and dark matter halo profiles. The NFW and Dekel–Zhao (DZ) models yield broadly consistent total masses ranging from 1.12(+0.11/-0.10) to 1.63(+0.21/-0.17)x10^12 Msun for beta=0.3–0.7. In contrast, the Einasto profile favors substantially lower masses of 0.41(+0.09/-0.06) to 0.86(+0.21/-0.16)x10^12 Msun, highlighting significant dependence on the adopted halo profile, although Einasto solutions are more in tension with independent mass estimates based on M31 satellite galaxies than the NFW and DZ models at fixed beta. Overall, our analysis provides a comprehensive measurement of M31's mass distribution under the assumption of dynamical equilibrium, while also quantifying the systematic uncertainties associated with halo velocity anisotropy and the choice of dark matter density profile.
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All authors Hao Wu, Yang Huang, Huawei Zhang, Qikang Feng, Cheng Liu

Monday 21 September

Astrophysics of Galaxies · Cross-listed from astro-ph.EP

1I/'Oumuamua-like objects's SFDs with older, current and future surveys

Rodrigo Albornoz-Montenegro and César Fuentes

Interstellar Objects (ISOs) may provide direct evidence of planetesimals ejected from early-stage solar systems. Studying these objects and predicting their detection through various surveys is vital for enhancing our understanding of planetary formation. We show how ISO size distribution (SFD), f_D~D^-q, controls expected detections in current and future surveys. We focus on TESS and the Vera Rubin Observatory LSST while analyzing Pan-STARRS and ATLAS. TESS is expected to detect ~1 ISO from shallow SFDs (q<2.5). On the other hand, LSST is likely to detect ~0.2-100 ISO yr^-1 over its lifetime. ATLAS is likely to detect one non-cometary object for populations with q<3. We further estimate ~0-8 detections of cometary like-3I/ATLAS objects by LSST in 10 years and ~1 cometary object detected by TESS over its mission time, independent of the nucleus size distribution. By considering both 1I/'Oumuamua and 3I/ATLAS from the same SFD, our results suggest that more asteroid-like objects are produced rather than comets during the early stages of planetary formation. Imminent detections of ISOs by LSST will help constrain the slopes of the SFDs for asteroid-like and cometary ISOs better, and, if applicable, differentiate between them.
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Astrophysics of Galaxies

PEGASUS (Pfs Emission-line GAlaxy SUrvey with Subaru): I. Three-dimensional large-scale structures at $z > 1$ probed with emission-line galaxies

Mariko Kubo, Tadayuki Kodama, Rhythm Shimakawa et al. (+16 more)

To comprehensively understand the environmental effects on galaxy evolution, it is crucial to precisely map the distribution and thoroughly examine the properties of galaxies, including low-mass building blocks. Deep narrow-band imaging observations conducted with Hyper Suprime-Cam (HSC) on the Subaru Telescope systematically probed the distribution of low-mass star-forming galaxies as H$\alpha$, [O {\footnotesize II}], and [O {\footnotesize III}] emission-line galaxies at $0.4\leq z\leq1.6$. We perform a comprehensive spectroscopic follow-up observation of these emission-line galaxies with narrow-band-based emission-line fluxes $\geq 2\times10^{-17}$ erg s$^{-1}$ cm$^{-2}$ within $\approx1.8$ deg$^2$ area centered on the COSMOS field using `Ōnohi`ula - Prime Focus Spectrograph (PFS) on the Subaru Telescope. In this paper, we outline the data product and present the large-scale structures at $z>1$. 9079 out of 9917 of the targets are observed, and the redshifts of 92%~of the observed targets are successfully confirmed. We survey groups, filamentary large-scale structures, and voids at $z=1.19$, $1.47$, and $1.60$ based on the three-dimensional distribution of $520-920$ [O {\footnotesize II}] emission-line galaxies with stellar masses $M_\star\geq10^{9.5}~M_{\odot}$ at each redshift. Groups with halo masses $1\times10^{12}-6\times10^{13}~M_{\odot}$ are identified along the filaments, whereas the most massive groups are located at the densest intersections of filaments as predicted by cosmological simulations. Voids hidden on the surface density maps are robustly extracted on the volume density map. Our spectroscopic sample provides a powerful basis for quantifying the evolution of galaxies along the diverse environments back in time toward cosmic noon epoch in forthcoming papers.
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All authors Mariko Kubo, Tadayuki Kodama, Rhythm Shimakawa, Yusei Koyama, Masato Onodera, Akio K. Inoue, Hisakazu Uchiyama, Tohru Nagao, Ken-ichi Tadaki, Ronaldo Laishram, Ryoma Wagatsuma, Chen Nuo, Haruka Kusakabe, Satoshi Kikuta, Yuma Sugahara, Kentaro Motohara, Kazuki Daikuhara, Ken Osato, Yongming Liang

Astrophysics of Galaxies

CHASE Spectral Survey I: Measuring Contamination in the Color-selected J-region Asymptotic Giant Branch Distance Indicator

Siyang Li, Alexei V. Filippenko, Arief Ahmad et al. (+11 more)

The J-region asymptotic giant branch (JAGB) method for distance measurements uses the near uniform luminosity of carbon-rich AGB stars as a standard candle. Its application rests on an assumed but rarely examined premise: the stars contained in the JAGB color-magnitude selection box are primarily carbon-rich AGB stars. We investigate the purity of the photometric selection in the Milky Way with an optical spectroscopic survey (~3590-7150 $\mathring{A}$) called CHASE (Carbon stars, Hubble tension, And Spectroscopic Exploration of JAGB populations) using the Shane 3 m telescope at Lick Observatory. These stars are classified using molecular bandhead step indices, which recover 100% of known classifications. We report the observations of 76 stars (54 within the standard JAGB selection box of 1.5 < J - K < 2.0 mag) and find only 13 of 54 stars are carbon-rich, a 76$\pm$6 oxygen-rich contamination under blind photometric selection. This contamination remains high (71%) even within $\pm$0.4 mag of the JAGB peak itself, showing it is not confined to the edges of the selection box. This inhomogeneity may explain why recent literature find field-to-field and methodological variations of 0.1-0.2 mag that now dominate its systematic error budget. These variations could be caused, in part, by inhomogeneous stellar populations that consist of differing spectral types, and hence differing mean magnitudes.
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All authors Siyang Li, Alexei V. Filippenko, Arief Ahmad, Adam G. Riess, Stefano Casertano, Thomas G. Brink, Richard Anderson, Caroline D. Huang, Louise Breuval, Noriyuki Matsunaga, Gracelynn Jost, Yash Mehta, Elaina Sadler, Julian Shapiro

Astrophysics of Galaxies

SALVAGE II: no systematic molecular gas depletion in the central 2 kpc of AGN hosts

Scott Wilkinson, Chiara Circosta, Toby Brown et al. (+5 more)

In cosmological simulations, active galactic nuclei (AGN) feedback is found to be necessary for the shutdown of galaxy-wide star-formation by heating and/or removing molecular gas. However, at low-redshift, there is little evidence of systematic large-scale gas depletion. Some recent observations have found molecular gas depletion in AGN hosts, but limited to the central regions of galaxies. In this work, we use the SDSS-ALMA Legacy-Value Archival Gas Exploration (SALVAGE) dataset, which provides molecular gas and stellar mass measurements from the inner (r < 0.5-2 kpc) and outer region of the galaxy. Using AGN diagnostics from optical emission lines, mid-IR colour, and X-ray luminosity, we identify 70 AGN at z < 0.07 and inspect their central molecular gas reservoirs with a suite of metrics compared to non-AGN controls. In agreement with global studies of low-z AGN hosts, we find that, compared to matched non-AGN, the central regions of AGN have equal molecular gas fractions and enhanced molecular gas surface densities. For the first time, we explore the central gas reservoirs of AGN identified with different selection criteria and find two optical AGN classes that show a tentative 1.5$\sigma$ and 1.8$\sigma$ signal of central molecular gas depletion. However, the AGN with central gas depletion do not occupy any specific region of the parameter space, such as AGN luminosity, that can provide a physical explanation for the depletion. If AGN are responsible for large-scale gas removal, the lack of systematic gas depletion in SALVAGE AGN sets an upper limit on the physical scale of the gas removal while the AGN remains observable.
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All authors Scott Wilkinson, Chiara Circosta, Toby Brown, Sara L. Ellison, Shoshannah Byrne-Mamahit, Almudena Alonso-Herrero, Santiago Garcia-Burillo, Federico Esposito

Astrophysics of Galaxies

Calcium Triplet Absorption is Common around Little Red Dots

Jenny E. Greene, Hanpu Liu, Raphael E. Hviding et al. (+29 more)

We present new evidence for an optically thick atmosphere surrounding Little Red Dots (LRDs) in the form of Ca absorption at rest-frame 8500A, the calcium triplet (CaT). Building on the detection of CaT absorption in one local LRD analog (the "Egg", Lin et. al. 2025), we investigate the region around rest-frame 8500A for an archival sample of 17 LRDs ($2 < z < 5$) with JWST/NIRSpec grating data. We detect CaT absorption in three individual sources, and find that on average there is an absorption equivalent width (EW) EW$_{\rm CaT} \approx -5$ A. Among the three detections, two are approaching the deepest absorption seen in integrated light from stars. Given that the continuum around CaT is probably dominated by the central engine, we argue that the absorbers are likely to be associated with the LRD. Such absorption has not historically been associated with any components of an AGN central engine, but a cool, optically thick photosphere as proposed for LRDs would naturally produce such absorption. The EW$_{\rm CaT}$ that we observe can be matched by hydrostatic atmosphere models at relatively low metallicity ([M/H]$<-1$) combined with an effective temperature $T_{\rm eff} > 4500$ K. Alternatively, the distribution can be matched at a low photospheric gas density $\rho_{\rm ph}<10^{-11}{\rm~g~cm^{-3}}$ that requires a non-hydrostatic gas structure on dynamical grounds. In the future, metal absorption lines should be a powerful complementary probe of the gas conditions, and possibly the enclosed mass, of LRDs.
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All authors Jenny E. Greene, Hanpu Liu, Raphael E. Hviding, Rohan P. Naidu, David J. Setton, Bingjie Wang, Ivo Labbe, Vasily Kokorev, Xiaojing Lin, Hollis B. Akins, Anna de Graaff, Joel Leja, Jorryt Matthee, Alberto Torralba, Karl Glazebrook, Rachel Bezanson, Leindert A. Boogaard, Gabriel Brammer, Caitlin M. Casey, John Chisholm, Xiaohui Fan, Lukas Furtak, Seiji Fujimoto, Yan-Fei Jiang, Yilun Ma, Themiya Nanayakkara, Erica J. Nelson, Richard Pan, Eliot Quataert, Anthony J. Taylor, Christina Williams, Adi Zitrin

Astrophysics of Galaxies · Cross-listed from astro-ph.SR

Using Machine Learning to Model Stellar Collisions in our Galactic Center

Tristan C. Sand, Sanaea C. Rose, Elena González Prieto et al. (+9 more)

Direct collisions in the inner pc of the Galactic center can alter the orbits and properties of stars. The outcome of a collision depends on a number of parameters, including the masses and ages of the stars, the impact parameter, and the initial relative velocity. We utilize the newly developed $\verb|collAIder|$, a machine learning tool developed to predict the outcomes of stellar collisions, to bridge 3D hydrodynamic simulations of stellar collisions with a dynamical model of the Galactic center. Our results show a substantial population of stripped stars, $\sim$$10\%$ of the initial stellar population, produced by mass loss during high-speed collisions. Stellar mergers are less frequent, with about $5\%$ of the stars experiencing a collision-induced merger. We also find that high-speed, nearly head-on collisions can completely disrupt the stars. These destructive collisions are usually preceded by 10 or more collisions, which gradually reduce the mass of the star before it is ultimately destroyed. We estimate that mass loss during stellar collisions injects roughly $(2.5-8)\times 10^5$ M$_\odot$ of gas into the surrounding environment. Most of this gas is injected into the inner $0.1$ pc and about $90\%$ is retained within the cluster and may be accreted onto the supermassive black hole.
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All authors Tristan C. Sand, Sanaea C. Rose, Elena González Prieto, James C. Lombardi, Jr., Charles F. A. Gibson, Fulya K{\i}roğlu, Kyle Kremer, Christopher E. O'Connor, Enrico Ramirez-Ruiz, Frederic A. Rasio, Tjitske Starkenburg

Astrophysics of Galaxies

A radial basis of massless potential-density pairs

E.V. Polyachenko and I.G. Shukhman

In the matrix method for linear perturbations of spherical stellar systems, the perturbed potential and density are expanded over a set of potential-density pairs. For radial perturbations, mass conservation makes the coefficient of $1/r$ in the perturbed potential vanish, so that the potential decays faster than $1/r$. Starting from the $\ell=0$ Hernquist–Ostriker family, we construct in closed form a set of potential-density pairs whose potentials decay as $r^{-p}$ with a prescribed $p\ge2$, the tail containing all subsequent integer powers. For $p=2$ each pair is individually massless, and the potential of the $n$-th pair is expressed through a single Jacobi polynomial. We derive the combination weights, the leading tail coefficients and the Gram matrix analytically; the Gram matrix is banded with half-width $p-1$ (tridiagonal at $p=2$). The $n$-th potential element has exactly $n-1$ nodes, spread from $r\sim n^{-2}$ to $r\sim n^{2}$, so that the set resolves both the centre and the far periphery. As a test, the expansion of the dilation-mode potential of the isochrone model converges exponentially and carries no parasitic mass at any truncation, in contrast to the standard set.
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Astrophysics of Galaxies

First Trigonometric Parallax Measurements with the KVN and VERA Array (KaVA)

Nobuyuki Sakai, Daisuke Sakai, Noriyuki Kawaguchi et al. (+26 more)

To demonstrate the astrometric capability of the combined Korean VLBI (Very Long Baseline Interferometry) Network (KVN) and VLBI Exploration of Radio Astrometry (VERA) Array (KaVA), we conducted six-epoch VLBI observations of 22-GHz H$_{2}$O masers associated with the star-forming region W3(OH). Two atmospheric calibration methods, (1) GPS and (2) JMA (Japan Meteorological Agency) mesoscale analysis data, and two phase-reference sources were independently applied to the astrometric analysis. Trigonometric parallaxes of W3(OH) were successfully measured with all calibration strategies, including the first successful parallax measurement using JMA calibration. The combined-fit parallax is 0.497$\pm$0.024 mas, corresponding to a distance of 2.01$^{+0.10}_{-0.09}$ kpc. This value is consistent with the previous Very Long Baseline Array (VLBA) result of 0.489$\pm$0.017 mas. KaVA achieved a 55$\%$ higher signal-to-noise ratio in phase-referenced maps than VERA, in good agreement with theoretical expectations. These results suggest that KaVA will enable trigonometric parallax measurements of 22-GHz H$_2$O masers that are difficult to observe with VERA alone because of low flux densities and/or limited $uv$ coverage. A flux variation from 510\,$\pm$\,50 to 3900\,$\pm$\,400 Jy was detected in W3(OH) over a one-year observing campaign and is attributed to two nearby maser features separated by only $\sim$64 AU at 2.01 kpc. The brightest feature showed a decrease in linewidth with increasing peak flux density, consistent with unsaturated maser amplification, whereas no similar trend was found for the other feature, suggesting different responses to the same amplification conditions, possibly owing to differences in saturation state and internal velocity structure.
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All authors Nobuyuki Sakai, Daisuke Sakai, Noriyuki Kawaguchi, Shuangjing Xu, Bo Zhang, Taehyun Jung, Chungsik Oh, Jeong-Sook Kim, Soon-Wook Kim, Hiroshi Imai, Yuanwei Wu, Maria Rioja, Niu Liu, Zehao Lin, Ibnu Nurul Huda, Shuaibo Bian, Leonid Petrov, Jingdong Zhang, Takaaki Jike, Yoshiaki Tamura, Jeong Ae Lee, Hao Ding, Koichiro Sugiyama, Kazuhiro Hada, Kiyoaki Wajima, Kazuya Hachisuka, Mareki Honma, Kee-Tae Kim, Se-Jin Oh

Astrophysics of Galaxies

Giant Low-Surface Brightness Galaxies in the Global Picture of Galaxy Formation and Evolution

Fedor M. Kolganov, Igor V. Chilingarian, Anna S. Saburova et al. (+5 more)

Giant low-surface brightness galaxies (gLSBGs) challenge standard merger-driven galaxy assembly models due to their large, dynamically cold disks, with radii often larger than 100~kpc and dynamical masses exceeding ${\sim}10^{12}$~\Ms. We identify $60$ gLSBGs, including a volume-complete subsample of $35$ galaxies out to $z=0.1$ in the 120~sq.deg. area. Using new and archival photometric and spectroscopic data, we homogeneously analyze their structural properties and derive central velocity dispersions. We update the gLSBG volume density estimate in the local Universe to $(3.6 \pm 0.6) \cdot 10^{-5}~\text{Mpc}^{-3}$. This number corresponds to about 1 in 4000 galaxies in the $g$-band luminosity range $0.14-1.37 \cdot 10^{11}~L_{\odot}$ out to $z=0.1$, which is consistent with EAGLE cosmological simulations but 3.8 times lower than the corresponding value in TNG100. Central surface brightness and scalelength of the gLSB disks scale with the luminosity of the central component, becoming fainter and flatter as the central component grows more luminous, suggesting rapid disk formation rather than the inside-out growth typical of high surface brightness late-type galaxies. Many gLSBGs also show extended UV counterparts in GALEX, strengthening their connection to XUV-disk galaxies. Finally, comparison with superluminous spirals shows that even complete gas-to-star conversion cannot transform a typical gLSBG into a superspiral, owing to their lower total baryonic mass.
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All authors Fedor M. Kolganov, Igor V. Chilingarian, Anna S. Saburova, Damir Gasymov, Evgenii V. Rubtsov, Vladislav I. Klochkov, Kirill A. Grishin, Mariia Demianenko

Astrophysics of Galaxies · Cross-listed from astro-ph.SR

The oldest low-$\alpha$ thin disc stars

Riano E. Giribaldi, Laura Magrini, Marco Palla et al. (+1 more)

The formation pathway of the $\alpha$-poor Milky Way thin disc remains under debate. The latest observational data indicates the presence of comparable numbers of old stars in both the low- and high-$\alpha$ disc components, suggesting either coeval or overlapping formation epochs. Using GALAH DR4, we provide evidence that the $\alpha$-poor stars coexist with $\alpha$-rich stars up to $\sim$12.5 Gyr. Stellar ages of 0.5 Gyr precision were re-derived for nearly $30\,000$ subgiant stars using accurate effective temperatures ($T_{\rm{eff}}$) from the infrared flux method (IRFM) together with distances based on Gaia parallaxes. About 22% of the sample constitutes a population peaking at 9.2 Gyr, with evidence for an extended old-age tail reaching 12.5 Gyr. Among stars older than 10 and 11 Gyr, between 20 and 30% have relative low [$\alpha$/Fe] and solar-like metallicities ($-0.5 \leq \mathrm{[Fe/H]} \leq +0.5$ dex). These stars exhibit kinematics consistent with those of near solar-age $\alpha$-poor stars in the thin disc. These stars can be evolved Sun-like stars, i.e. old solar analogues, whose $T_{\rm{eff}}$ and gravity modified with the time. Comparison with a well-tested Galactic disc chemical evolution model supports the presence of a significant fraction of old, $\alpha$-poor disc stars, confirming the plausibility of our selection criteria. We provide a catalogue with the selected sample to facilitate spectroscopic follow-ups at high resolution.
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All authors Riano E. Giribaldi, Laura Magrini, Marco Palla, Carlos Viscasillas Vázquez

Astrophysics of Galaxies

Gone with the wind? Potential gas inflow in the broad-line region of a QSO at $z=0.287$ traced by time-varying Balmer absorption

Xihan Ji, Dominic J. Walton, Francesco D'Eugenio et al. (+6 more)

We report spectroscopic observations of a remarkable QSO, J115724.80-000455.56 at $z=0.287$ from the Dark Energy Spectroscopic Instrument (DESI) survey. This QSO exhibits variability in its hydrogen Balmer absorption over a time interval of 10 months in the observed frame between 2021 and 2022. The observed Balmer absorption can be decomposed into two components with distinct kinematics: a non-varying, "stationary" component and a varying, "dynamic" component. Both absorbers have gas column densities of $N_{\rm H}\sim 10^{22}~{\rm cm^{-2}}$ and likely have densities of $n_{\rm H}\gtrsim 10^{8}~{\rm cm^{-3}}$. We inferred small effective physical sizes of $\lesssim 10^{-3}$ pc for the absorbers, which, together with the time variability, suggests that the absorption occurs in the broad-line region (BLR). The reshifted centroid velocities of both absorbers imply an inflow, where the inferred mass inflow rate is comparable to the single-epoch mass accretion rate of this QSO. The 2022 epoch of this QSO further reveals a 10% change in the column density over 2 months, indicating the gas inflow might be continuous. We also obtained new X-ray observations using the $\it Einstein~Probe$, which reveals an X-ray-to-bolometric luminosity ratio significantly below the general AGN population. The X-ray weakness is consistent with strong gas obscuration with $N_{\rm H}= 4.0^{+ 1.6}_{- 1.5}\times10^{23}~{\rm cm^{-2}}$. The substantially higher gas obscuration seen in the X-rays compared to the optical possibly indicates a warm absorber inside the BLR or merger-driven enhancement of the galactic scale obscuration consistent with optical imaging. This QSO might thus represent an active feeding phase after a recent gas-rich merger.
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All authors Xihan Ji, Dominic J. Walton, Francesco D'Eugenio, Ignas Juodžbalis, Vasily Belokurov, Andrew C. Fabian, Roberto Maiolino, Jiamu Huang, Douglas N.C. Lin

Astrophysics of Galaxies

The KAGG survey: KCWI Analysis of Gas around Galaxies at z~3-5

Grecco A. Oyarzún, Marc Rafelski, J. Xavier Prochaska et al. (+5 more)

We present the KCWI Analysis of Gas around Galaxies (KAGG) survey of Ly$\alpha$ emission around Damped Ly$\alpha$ Absorbers (DLAs) at z~3-5 with the Keck Cosmic Web Imager (KCWI) integral-field spectrograph. The KAGG survey is characterized by the sample of 36 DLAs spanning a wide metallicity range, the wide search area for associated Ly$\alpha$ emission (impact parameter b$~\lesssim 120~$kpc), and the high emission sensitivity, reaching Ly$\alpha$ luminosities $\lesssim10^{42}$ erg s$^{-1}$. We identify 7 DLA Ly$\alpha$ emitters that are likely DLA galaxy candidates due to the good match between the Ly$\alpha$ emission and DLA redshifts. Based on a composite sample of 11 DLA Ly$\alpha$ emitters from KAGG and MAGG (MUSE Analysis of Gas around Galaxies), we find that the impact parameters of DLA Ly$\alpha$ emitters decrease with DLA metallicity, from b$~>50~$kpc at [M/H]~-2 to b$~<50~$kpc at [M/H]~-1. Including Ly$\alpha$ emitters at larger velocity offsets and at larger impact parameters from the DLAs, we construct samples of 35 "Group" Ly$\alpha$ emitters and 17 "Large-scale" Ly$\alpha$ emitters. We find that their impact parameters and incidence rates also depend on DLA metallicity. Based on simulations of our survey and comparisons with models of galaxy formation, we conclude that higher DLA metallicities are associated with higher halo masses. The low Ly$\alpha$ emission detection rate at low impact parameters suggests that most DLA galaxies either have low stellar masses (M$~\lesssim10^{8}M_{\odot}$) or have their Ly$\alpha$ emission suppressed due to HI resonant scattering and/or dust absorption.
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All authors Grecco A. Oyarzún, Marc Rafelski, J. Xavier Prochaska, Nissim Kanekar, Marcel Neeleman, Marie Wisz, Michele Fumagalli, Regina A. Jorgenson

Astrophysics of Galaxies

Dark matter haloes from dwarf to massive galaxies: no systematic inner-density tension with {\Lambda}CDM hydrodynamical simulations

Pavel E. Mancera Piña, Justin I. Read, Jorge Sarrato-Alós et al. (+1 more)

Two of the most prominent small-scale challenges to the cold dark matter (CDM) paradigm are the cusp-core and diversity-of-rotation-curves problems. The former concerns the shallow inner DM density profiles inferred for many galaxies compared with the cusps predicted by collisionless CDM, while the latter concerns the wider range of inner DM densities and rotation curve shapes inferred observationally than hydrodynamical simulations traditionally reproduce. Robust observational constraints on DM core sizes and halo densities are therefore essential for testing both the nature of DM and the impact of galaxy formation processes. We analyse the inner DM distribution of a curated sample of 48 gas-rich galaxies and 8 Milky Way gas-poor satellites, spanning 6 orders of magnitude in $M_\ast$. We find substantial scatter in DM core sizes and degrees of coreness, with both cuspy and cored haloes occurring over a broad $M_\ast$ range. The cores are energetically consistent with stellar feedback, requiring modest supernova energy coupling efficiencies of order $0.1-1\%$. Comparisons with the NIHAO, FIRE-2, and EDGE simulations reveal broad agreement in the inner DM densities and logarithmic slopes of observed and simulated galaxies. The main residual differences concern the steep slopes of some massive simulated galaxies and differences in SHMRs. Using a rotation-curve diversity diagnostic from previous work, we find that extreme discrepancies with simulations are absent from our curated sample and largely attributable to uncertain kinematics or baryonic mass distributions. Within the scope of our analysis, we find no evidence of a systematic inner-density tension between our galaxy sample and current $\Lambda$CDM hydrodynamical simulations. Together with the modest energetic requirements for core formation, this substantially alleviates the cusp-core and diversity-of-rotation-curves problems.
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All authors Pavel E. Mancera Piña, Justin I. Read, Jorge Sarrato-Alós, Claudia Muni

Astrophysics of Galaxies

CRIMSONS: An Online Tool for Modeling Chemical Enrichment with Stochastic IMF Sampling

Martina Rossi, Lapo Querci, Stefano Ciabattini et al. (+14 more)

Chemical enrichment is a universal process shaped by several interconnected factors, including stellar feedback, the nature of chemical polluters, and the underlying distribution of stellar masses. Three key ingredients are often difficult to treat simultaneously in chemical-evolution models: the stochastic sampling of the stellar IMF, uncertainties in stellar nucleosynthesis yields, and pre-enrichment from primordial PopIII stars. In low star-formation rate environments, incomplete IMF sampling makes enrichment sensitive to the random presence or absence of massive supernova progenitors. Here, we present CRIMSONS, the first online tool designed to model chemical enrichment while self-consistently incorporating these three ingredients. The framework allows users to explore different IMFs, stellar population masses and metallicities, and multiple stellar yield sets. It follows the evolution of individual stars and tracks 30 elements(H-Zn), including contributions from SN, AGB stars, and TypeIa SNe. The current implementation adopts a closed-box framework, neglecting gas flows and spatial mixing, thus providing a controlled setup to isolate the effects of IMF sampling, stellar yields, and PopIII pre-enrichment. With CRIMSONS, we show that incomplete IMF sampling produces large abundance scatter, particularly in low-mass stellar populations. Different yield prescriptions introduce element-dependent variations, while some abundance ratios remain comparatively robust across models. Finally, comparison between models including primordial enrichment and those adopting only a metallicity floor shows that PopIII pre-enrichment can significantly affect subsequent chemical evolution. CRIMSONS therefore provides a controlled framework for quantifying the relative impact of stochastic IMF sampling, nucleosynthetic uncertainties, and primordial pre-enrichment on predicted abundance patterns
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All authors Martina Rossi, Lapo Querci, Stefano Ciabattini, Stefania Salvadori, Irene Vanni, Davide Massari, Edoardo Ceccarelli, Donatella Romano, Viola Gelli, Raffaele Pascale, Alice Mori, Elka Rusta, Ioanna Koutsouridou, Ása Skúladóttir, Laura Magrini, Riano Giribaldi, Jose Schiappacasse-Ulloa

Astrophysics of Galaxies

EPOCHS-DR2 I: Expanded data release and properties of $6.5<z<16.5$ photometrically selected galaxies across NIRCam deep fields covering $\sim700\,\rm arcmin^2$ with the galfind software

Duncan Austin, Christopher J. Conselice, Thomas Harvey et al. (+14 more)

We present the \epochstwo\ sample of $2452$ star forming galaxies at $6.5<z_{\rm phot}<16.5$ produced using the \galfind\ photometric pipeline across $\sim650-740~\mathrm{arcmin}^2$ in six of the most widely used deep, blank field \jwst/NIRCam imaging surveys. $293$ galaxies are spectroscopically confirmed and a spectroscopic–photometric redshift comparison yields a normalized median absolute deviation, $\sigma_{\rm NMAD}=0.017$, an $\eta=4.3\%$ outlier rate, and a mean offset $\langle\Delta z\rangle=-0.022$. We find $34$ little red dots (LRDs) with “V–shaped” SEDs, as well as $69$ L–type, $36$ T–type, and $2$ compact Y–type brown dwarf candidates, which we remove from our sample. The fiducial sample yields a flattening $\beta_{\rm UV}-M_{\rm UV}$ relation with only moderately blue median $\beta_{\rm UV}(M_{\rm UV}=-19)=-2.32^{+0.08}_{-0.07}$ at $z\simeq12.5$, implying dust-polluted stellar populations at the highest redshifts. A “gold” sample of $62$ sources are identified at $z_{\rm phot}>10.5$, $\sim85\%$ of which are without NIRSpec follow-up, including $15$ candidates at $z_{\rm phot}>13.5$ across a diverse range of proper sizes $30\,\rm pc\lesssim r_{\rm c}\lesssim1.5\,\rm kpc$ and UV slopes $-4.0\lesssim\beta_{\rm UV}\lesssim-1.5$. Two very promising candidates stand out, GS-W-4608 and GN-Med-1881, with $\beta_{\rm UV}\lesssim-3$, $\gtrsim1.6\,\rm mag$ \lya\ break colors, and F335M and F410M detections which improve their high-redshift solution robustness. Complementary to our high-redshift sample, this public data release provides the community with optical/NIR catalogs, empirical PSFs, and \eazypy, \bagpipes, and \bdfinder\ SED fitting results, enhancing the legacy value of photometric JWST data in the upcoming era of wide-field imaging datasets with Euclid and Roman.
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All authors Duncan Austin, Christopher J. Conselice, Thomas Harvey, Nathan J. Adams, Louis Quilley, Jordan C. J. D'Silva, Vadim Rusakov, Qiong Li, Lewi Westcott, Caio Goolsby, James Arcidiacono, Kai Madgwick, William J. Roper, Brenda Frye, Norman A. Grogin, Rafael Ortiz III, Rogier Windhorst

Astrophysics of Galaxies

Galaxy evolution in the post-merger regime. V - Atomic gas evolution traced by ALFALFA stacks

Sara L. Ellison, Manasvee Saraf, Leonardo Ferreira et al. (+4 more)

(Abridged) In this work, we investigate the role of atomic hydrogen (HI) gas in the galaxy merger lifecycle. In order to both identify galaxies in mergers, as well as to predict their time since coalescence, we present an extension of the MUlti Model Merger Identifier (MUMMI) machine vision pipeline applied to Dark Energy Camera Legacy Survey (DECaLS) imaging. The new MUMMI-DECaLS catalog contains 19,951 post-mergers, of which 14,638 have robust time post-merger (T_PM) predictions. The MUMMI-DECaLS post-merger galaxy catalog is cross-matched with the Arecibo Legacy Fast ALFA (ALFALFA) survey. For the 752 post-mergers thus identified, as well as a matched control sample, we produce median spectral stacks of 21~cm emission, finding that the post-mergers are HI deficient by 0.11 dex compared with non-interacting galaxies. When divided into T_PM bins we find that the HI deficit (or excess) is strongly dependent on both the time since coalescence and whether the galaxies are star-forming or quenched. Star-forming post-mergers in particular show a strong HI evolution with T_PM, exhibiting a 0.1 dex MHI excess immediately after coalescence, a 0.3 dex MHI deficit at 0.16 < T_PM < 0.96 Gyr and normal gas masses by ~ 1.5 Gyr after coalescence. On the other hand, despite being matched in star formation rate, stellar mass and redshift, quenched post-mergers are HI deficient at both short and long post-coalescence times. Nonetheless, a significant mass of HI (>10^9 M_sun) remains even in these late-time quenched post-mergers, representing a resource which could potentially re-fuel star formation in the future. Our results demonstrate the complexity of quantifying the HI behaviour in mergers, which depends not only on timing, but also star-forming status, which can complicate comparisons between different studies and samples.
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All authors Sara L. Ellison, Manasvee Saraf, Leonardo Ferreira, Amelie Saintonge, Dirk Scholte, Jing Wang, Qifeng Huang

Astrophysics of Galaxies

Reducing False Positives in Strong-Lens Searches with Generalized-Mean Consensus of Machine-Learning Ensembles in the Kilo-Degree Survey

Ziqi Li, Rui Li, Xu Huang et al. (+11 more)

Context. In wide-field surveys, the main challenge is not just classifier sensitivity, but the overwhelming number of false positives. Searching for strong lenses among millions to bilions of galaxies produces many contaminants, making the bottleneck for follow-up inspection and building statistically useful lens samples. Aims. We aim to improve the purity of strong-lens candidate selection in KiDS DR4 by combining several classifiers. The objective is to retain high completeness for known candidates while substantially reducing the fraction of non-lenses. Methods. We trained convolutional, Transformer-based, and hybrid classifiers, including Li ResNet+, Swin Transformer variants, Swin-MLP, and DemiLensNet. Their probabilistic outputs were combined at score level using averaging and a generalized mean consensus. The models were tested on simulated KiDS-like lens images and then evaluated on real KiDS DR4 lens candidates embedded in a non-lens sample. Results. On the simulated test set, ensembles show no advantage over the best single models. On the mixed real KiDS test set, the arithmetic mean reduces the false-positive rate at 90% completeness from 0.016-0.020 (the range spanned by the two best individual models) to 0.011 for the seven-model ensemble. The generalized mean reduces it further, to 0.007. Applied to the full LRG and BG samples at the same 90% completeness level, the generalized mean reduces returned candidates by roughly 50% for LRGs and 70% for BGs, relative to the best single model. After visual inspection, we obtain 170 new high-quality candidates (24 Class A and 146 Class B), together with 1706 Class C candidates. Conclusions. Our results demonstrate that the generalized mean consensus of an ML ensemble strategy provides a practical route to reducing the visual inspection workload while preserving a high recovery rate of promising strong-lens candidates.
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All authors Ziqi Li, Rui Li, Xu Huang, Hui Li, Pufan Liu, Liang Gao, Crescenzo Tortora, Nicola N. Napolitano, Xiaoyue Cao, Ran Li, Liqing Chen, Kang Jiao, Valerio Busillo, Yue Dong

Astrophysics of Galaxies

A Newly Discovered VVVX Star Cluster Surfing the Galactic Disk

Elisa R. Garro, José G. Fernández-Trincado, Casmir O. Obasi et al. (+15 more)

We report the discovery of Garro 04, a previously unidentified stellar cluster toward the Galactic disc, uncovered as part of the ESO/KMOS VVVX-GalCen Spectroscopic Survey. This object was serendipitously confirmed as a stellar overdensity in the VISTA Variables in the Vía Láctea eXtended (VVVX) survey footprint and subsequently confirmed through medium-resolution $K$-band spectroscopy obtained with the K-band Multi Object Spectrograph (KMOS) at the ESO Very Large Telescope. The combined photometric and spectroscopic analysis reveals a coherent stellar population with common radial velocities and chemical properties, supporting its classification as a genuine star cluster rather than a statistical fluctuation of the disk field. We derive the fundamental properties of Garro 04, including its structural parameters, distance, kinematics, and compute its orbital properties, finding that its motion remains confined to the Galactic disk region. Finally, our analysis suggests that Garro~04 is likely an old open cluster, or an object straddling the boundary between the canonical globular and open cluster classifications, with an estimated Age $ = 5 \pm 2$ Gyr and a metallicity of $\mathrm{[Fe/H]} = -0.5 \pm 0.2$, finding an excellent agreement between the photometric and spectroscopic determinations.
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All authors Elisa R. Garro, José G. Fernández-Trincado, Casmir O. Obasi, Dante Minniti, Matías Gómez, Roberto K. Saito, Javier Alonso-García, Alonso Luna, Valentin D. Ivanov, Maria Gabriela Navarro, Sara Federle, Bernardo P. L. Pereira, Beatriz Barbuy, Devika Bhadrakumar Sindhu, Bruno Dias, Tali Palma, Ilaria Petralia, Sasi Saroon

Astrophysics of Galaxies

CAVITY: Calar Alto Void Integral-field Treasury surveY: II. Second public data release

B. Bidaran, A. Jiménez, R. García-Benito et al. (+30 more)

Studying galaxy evolution under the unique environmental conditions of cosmic voids provides an opportunity to disentangle the role of the large-scale environment in shaping mass assembly (both baryonic and dark matter), regulating galaxy physical properties, and driving the transformation from star-forming to quiescent systems. We present the second public data release (DR2) of the Calar Alto Void Integral-field Treasury Survey (CAVITY), an ongoing legacy programme designed to study void galaxies (VGs) across a range of nearby ($0.005 \leq z \leq 0.050$) voids with different sizes and dynamical stages, providing 200 science-grade optical integral-field spectroscopy (IFS) data cubes. By doubling the number of galaxies relative to DR1 while maintaining the same selection criteria, DR2 significantly increases the dataset's statistical power, enabling more robust characterization of galaxy properties and their correlations with environment. The observations were obtained with the PMAS/PPAK spectrograph on the 3.5-m Calar Alto telescope using the V500 configuration, covering the optical spectral range of 3745-7500 A at a resolution of 6 A (FWHM). The DR2 VG sample spans a broad range of stellar masses, morphologies, colours, and gas ionisation properties. We describe the sample selection, observing strategy, data reduction pipeline, quality-control procedures, and the public access to the CAVITY datasets and associated ancillary data on the survey's database. In addition, we present a characterisation of the large- and local-scale environments of CAVITY galaxies, showing that the 15 surveyed voids encompass a wide variety of sizes, galaxy richness, galaxy populations, and local structures, including galaxy groups. This release comprises 200 IFS data cubes, publicly available together with the master catalogues at the survey's dedicated webpage: https://cavity.caha.es/data/dr2/.
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All authors B. Bidaran, A. Jiménez, R. García-Benito, M. Argudo-Fernández, M. Alcázar-Laynez, S.B. De Daniloff, S. Duarte Puertas, D. Espada, E. Florido, Y. K. González-Koda, I. Pérez, T. Ruiz-Lara, L. Sánchez-Menguiano, G. Torres-Ríos, P. Vásquez-Bustos, S. Verley, A. Zurita, M. A. Canossa-Gosteinski, A. M. Conrado, H. M. Courtois, I. del Moral-Castro, J. Falcón-Barroso, A. Ferré-Mateu, M. Hernández-Sánchez, A. Lugo-Aranda, S. Subramanian, P. Villalba-González, L. Galbany, R. M. González Delgado, R. F. Peletier, S. F. Sánchez, R. van de Weygaert, A. Fernández-Martín

Astrophysics of Galaxies

Physical conditions in PDRs revealed by IGRINS ro-vibrational H2 observations

Aurélien Piluso, Vincent Maillard, Raphael Meshaka et al. (+10 more)

We compare H2 high ro-vibrational observations of 5 PDRs (S140, IC63, Horsehead Nebula, NGC 2023 and Orion Bar) obtained with the IGRINS spectrograph to PDR models produced with the Meudon PDR code, in order to estimate the physical conditions and to constrain the physical and chemical processes that govern PDRs. We use newly flux-calibrated and extinction-corrected IGRINS H2 observations covering the 1.45-2.45 um range at a resolution of 45000, and adjust Meudon PDR models using both a simple chi2 minimization approach and a robust method using Bayesian inversion followed by posterior exploration via an advanced MCMC technique. The PDR models use specific incident FUV spectra for each PDRs based on theoretical stellar spectra from the Pollux database. The Meudon PDR code is able to reproduce more than 85% of the observed H2 ro-vibrational line intensities within a factor of two. We find that (1) a realistic modeling of the incident FUV field (both in term of geometry and of spectral shape) and (2) the inclusion of recent data on collisional de-excitation rates for high vibrational levels of H2 are key to this success. H2 ro-vibrational emission lines are found to provide good constraints on both the thermal pressure and the incident FUV field strength, G0, although with a non-negligible remaining degeneracy in most PDRs. Additional constraints, such as the spatial scales of the PDR derived from ALMA or JWST observations, are found to be able to lift this degeneracy. For low excitation PDRs, the observations provide evidence that nascent H2 molecules formed on grains have relatively low rotational energy and high vibrational energy, as predicted by theoretical and experimental studies of the surface formation of H2.
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All authors Aurélien Piluso, Vincent Maillard, Raphael Meshaka, Emeric Bron, Franck Le Petit, Kyle Kaplan, Pierre Palud, Emilie Habart, Evelyne Roueff, Jacques Le Bourlot, Aristide Doussot, David Languignon, Nicolas Moreau

Astrophysics of Galaxies

LATED: JWST integral field spectroscopy of a galaxy caught in chemical infancy at $z=4.8$ behind Abell 2744

Mingyu Li, Roberto Maiolino, Zheng Cai et al. (+26 more)

When Population III (Pop III) star formation ended remains an open question. LATED-1 is an intrinsically faint ($M_\mathrm{UV}=-16.15$) Ly$\alpha$ emitter at $z=4.80$ revealed by VLT/MUSE behind the lensing cluster Abell 2744 ($z=0.308$). Before any spectroscopic metallicity constraints, it was identified as an extremely metal-poor or metal-free galaxy candidate from JWST imaging by LATED, our novel photometric selection framework. Here we present serendipitous JWST/NIRSpec PRISM integral-field spectroscopy of this target. The spectrum reveals Ly$\alpha$, H$\beta$, and H$\alpha$ at 7.0, 5.6, and 17.7$\sigma$, as well as tentative detections of [O III]$\lambda\lambda4959,5007$ at 2.9$\sigma$, and yields $R3=\mathrm{[O\,III]\lambda5007/H\beta}=0.59^{+0.27}_{-0.21}$, upholding the earlier LATED photometric prediction of $R3<1.54$ ($2\sigma$ limit). The canonical JWST-based strong-line calibration, extrapolated to low metallicity, implies $\log (O/H)=6.45^{+0.17}_{-0.19}$, or $Z/Z_\odot=0.58_{-0.20}^{+0.28}\%$, placing LATED-1 among the most metal-poor galaxies known. Its modest magnification ($\mu=2.80$) leaves the intrinsic properties insensitive to the lens model. LATED-1 is therefore a dwarf galaxy caught in the earliest state of chemical enrichment, and a compelling target for testing whether Pop III star formation can persist to $z<5$. The result demonstrates that photometric selection, especially through the LATED methodology, can reach below one per cent solar metallicity to identify Pop III galaxy candidates for spectroscopic follow-up.
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All authors Mingyu Li, Roberto Maiolino, Zheng Cai, Hannah Übler, Boyuan Liu, Qiao Duan, Fuyan Bian, Sijia Cai, Francesco D'Eugenio, Eiichi Egami, Bjorn H. C. Emonts, Xiaohui Fan, Yuki Isobe, Lucy R. Ivey, Xihan Ji, Gareth C. Jones, Maria Koller, Xiaojing Lin, Christopher C. Lovell, Kimihiko Nakajima, Masami Ouchi, Robert G. Pascalau, J. Xavier Prochaska, Jan Scholtz, Fengwu Sun, Sandro Tacchella, Yunjing Wu, Fujiang Yu, Zijian Zhang

Astrophysics of Galaxies

LATED: Ly$\alpha$-anchored photometric selection of candidate metal-free and extremely metal-poor star formation from the end of reionisation to cosmic noon

Mingyu Li, Zheng Cai, Roberto Maiolino et al. (+24 more)

Cosmological simulations allow a low-level tail of Population III (Pop III) star formation to persist to $z=2-6$. Spectroscopic confirmation is expensive, so an efficient photometric pre-selection is needed. We present LATED (Lyman-Alpha Tomography of Extremely Metal-poor Domains), which selects metal-free and extremely metal-poor candidates from a Ly$\alpha$-emitter parent sample using strong-line diagnostics. The method requires three bands and two colours, $x=m_{\rm OIII}-m_{{\rm H}\alpha}$ and $y=m_{{\rm H}\alpha}-m_{\rm cont}$, which trace oxygen abundance and the H$\alpha$ equivalent width, respectively. Requiring that the filters simultaneously contain [O III]+H$\beta$ and H$\alpha$, together with a Ly$\alpha$ parent selection, defines five windows spanning $z=1.92-6.60$ (four JWST/NIRCam, one Roman/WFI). The criteria, $x\geq x_{\rm min}(z)$ and $y\leq y_{\rm max}(z)$, are set by the per-redshift extrema of a forward-modelled Pop III template locus. Ordinary metal-enriched star-forming and AGN templates fall outside the selection region, and possible contaminants such as little red dots are flagged by their multi-band colours. To check contamination empirically, we apply LATED to 1126 JADES spectroscopic galaxies, and no source is selected in the four NIRCam windows. We release a Python package which converts the same photometry into R3=[O III]/H$\beta$ as a measurement or upper limit, reproducing JADES spectroscopy with small 0.12 dex scatter. Applied to 85 archival MUSE Ly$\alpha$ emitters in Abell 2744, LATED recovers the confirmed extremely metal-poor galaxy AMORE6 and reveals three new candidates at $z=3-5$. Photometry alone cannot establish a metal-free nature. LATED delivers prioritised candidates for spectroscopic follow-up, providing a scalable route toward a systematic census of late-time Pop III star formation.
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All authors Mingyu Li, Zheng Cai, Roberto Maiolino, Fuyan Bian, Sijia Cai, Francesco D'Eugenio, Qiao Duan, Eiichi Egami, Xiaohui Fan, Yuki Isobe, Xihan Ji, Gareth C. Jones, Maria Koller, Xiaojing Lin, Boyuan Liu, Christopher C. Lovell, Kimihiko Nakajima, Masami Ouchi, Robert G. Pascalau, Zijin Su, Jan Scholtz, Fengwu Sun, Sandro Tacchella, Hannah Übler, Yunjing Wu, Fujiang Yu, Zijian Zhang

Astrophysics of Galaxies · Cross-listed from astro-ph.SR

Companion masses of Gaia DR3 AstroSpectroSB1 binaries: a Bayesian forward-modelling framework

Prasid Sandave and Raghuveer Garani

Gaia Data Release 3 (DR3) has substantially expanded the study of unresolved binaries by providing combined astrometric and spectroscopic orbital solutions for a large sample of non-single stars. We present a Bayesian forward-modelling framework for estimating companion masses in Gaia DR3 AstroSpectroSB1 systems. The method samples the physical parameters of each binary, predicts the corresponding astrometric Thiele-Innes constants and spectroscopic orbital coefficients, and evaluates their likelihood using the full covariance matrix published by Gaia. An external prior on the primary mass is incorporated to resolve the remaining degeneracy between the component masses and orbital inclination in single-lined systems. We apply this framework to 1035 AstroSpectroSB1 systems with primary-mass estimates drawn from the Gaia DR3 astrophysical\_parameters table. Of these, 760 systems also have Gaia-reported estimates for both component masses and are used as a validation sample. The remaining 275 systems constitute an inference sample for which the mass of the fainter, unresolved companion is estimated. For systems with well converged posteriors, the inferred parameters reproduce the Gaia orbital observables, while the companion masses recovered for the validation sample are consistent with the Gaia estimates. In the inference sample we find 113 well converged systems for which the companion masses are meaningfully inferred. We find that the population is dominated by ordinary stars, together with a smaller high-mass tail that may contain massive white dwarfs or other compact-object candidates. Our framework provides a scalable approach for converting Gaia AstroSpectroSB1 solutions into companion-mass posterior distributions, identifying promising systems for targeted follow-up, and preparing for the larger and more precise orbital samples anticipated with Gaia DR4.
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Astrophysics of Galaxies

Gravity-driven Emergence of Multi-fractal Density Structure in the Orion A Integral Shaped Filament

Mengke Zhao, Guang-Xing Li, Keping Qiu et al. (+1 more)

Molecular clouds are often described as self-similar structures, although spatially averaged measures do not retain local variations in density scaling. We use the density exponent $\kappa_\rho$ ($\rho \propto r^{\kappa_\rho}$) to characterize the density structure of the Integral Shaped Filament (ISF) in Orion\,A. Applying the Multiscale Decomposition Reconstruction method to the Herschel column-density map, we find distinct density–scale relations across the connected filament. Their slopes steepen from $\kappa_\rho \approx -1.7$ to $-1.9$ in the quiescent OMC-4/5 regions, through $\approx -2.1$ in the star-forming OMC-2/3, to $\approx -2.3$ in OMC-1, which hosts massive star formation. The ISF therefore does not follow a single local density-scaling exponent but exhibits multi-fractal density scaling. The pixel-level distributions show the same progression toward higher volume density and more negative $\kappa_\rho$. Since $\kappa_\rho$ measures the concentration of gas toward smaller scales, we interpret this sequence as gravity-driven differential collapse: denser regions have shorter free-fall times and develop steeper density profiles. Longitudinal gas motions toward OMC-1 may limit the mass supply available for large-scale growth in the outer sub-regions and help maintain the observed range of local exponents. These results link local density scaling to gravitational concentration within a single connected filamentary system.
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All authors Mengke Zhao, Guang-Xing Li, Keping Qiu, Guangya Zeng