Astrophysics of Galaxies
Reconstructing the Projected Dark Matter Field across 0.1-100 Mpc Scales from the SDSS Survey
Kunyao Zhao, Yingjie Peng, Dingyi Zhao et al. (+16 more)
Dark matter sets the gravitational environment in which
galaxies form and evolve, but cannot be observed directly. We present a conditional
diffusion model that reconstructs the projected dark matter density field from the
galaxy stellar-mass density field for direct application to
galaxy surveys. The model is trained on CAMELS and validated on the independent IllustrisTNG300-1 simulation.
Halo masses inferred from the reconstructed projected-aperture measurements agree well with the corresponding true values, with a scatter below 0.2 dex. On 100 kpc scales, reconstructed surface densities show a typical scatter of ~0.3 dex in the regime most relevant for observations. We apply the model to SDSS
galaxies with $M_\star\ge10^9\,M_\odot$ in a contiguous low-
redshift region. Averaging over 100
stochastic realizations, we reconstruct and publicly release a projected dark matter field covering $90\times90\,(h^{-1}\mathrm{Mpc})^2$ with a pixel size of $0.097\,h^{-1}\mathrm{Mpc}$. This pixel area corresponds to the characteristic projected area of
halos with masses of ~$10^{10.6}\,h^{-1}\,M_\odot$. The map reveals the multiscale projected
cosmic web, including cluster-scale overdensities, filaments and voids. Projected-aperture masses are statistically consistent with SDSS group-catalog masses, while the derived
halo mass function broadly matches mock-catalog expectations. The reconstructed projected potential places Coma in one of the deepest wells and near a convergence region of the inferred projected acceleration field, suggesting that the reconstruction retains both local overdensities and coherent large-scale projected gravitational structure. This work shows that
diffusion-based dark matter reconstruction can be applied to real
galaxy surveys, enabling
halo-mass- and spatially resolved dark-matter-environment-based studies of
galaxy evolution in SDSS and future wide-area surveys.
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All authors Kunyao Zhao, Yingjie Peng, Dingyi Zhao, Xiaohu Yang, Luis C. Ho, Kai Wang, Jing Dou, Zeyu Gao, Qiusheng Gu, Yukun Liu, Roberto Maiolino, Houjun Mo, Alvio Renzini, Canpo Su, Bitao Wang, Yu-Chen Wang, Bingxiao Xu, Feng Yuan, Xingye Zhu
Astrophysics of Galaxies · Cross-listed from astro-ph.EP
JWST Reveals Refractory-Rich Water Ice in Interstellar Comet 3I/ATLAS: Evidence for a Continuum of Grain Properties across Protoplanetary Disks
Silvia Protopapa, Michael S. P. Kelley, Martin A. Cordiner et al. (+12 more)
We present JWST/NIRSpec PRISM observations of the interstellar comet 3I/ATLAS obtained on 2025 August 6 (Epoch 1), 2025 December 22 (Epoch 2), and 2026 April 1 (Epoch 3), spanning eight months around perihelion at heliocentric distances of 3.3, 2.4, and 5.7 au, respectively. The spectra reveal a broad 3 $\mu$m absorption band together with H$_2$O, CO$_2$, and CO gas emission. Unlike previously reported water-ice-rich Solar System comae, the strong 3 $\mu$m absorption is accompanied by weak or absent 1.5 and 2.0 $\mu$m water-ice bands. Spectral modeling indicates that the observations are best reproduced by submicron- to micron-sized water-ice-bearing aggregates containing refractory material. Compared with Epoch 1, the Epoch 3 spectrum favors the presence of a second population of larger, micron-sized, ice-rich aggregates and exhibits a subtle Fresnel-like structure near 3.1 $\mu$m, consistent with crystalline water ice. The observations can be explained by either crystalline water ice at both epochs, with the spectral
evolution arising primarily from changes in grain size and refractory mixing, or an
evolution from an amorphous-like to crystalline state. The spectral properties of 3I bridge those of water-ice-bearing Solar System comae and several spectral classes of mid-sized trans-Neptunian objects, suggesting that the icy building blocks of planetesimals formed in different protoplanetary disks may span a continuum in the physical state of water ice, ranging from pure ice grains to water-ice-bearing aggregates with varying refractory content at submicron-to-micron scales, with 3I extending toward the refractory-rich end of this continuum.
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All authors Silvia Protopapa, Michael S. P. Kelley, Martin A. Cordiner, Stefanie N. Milam, Dennis Bodewits, Steven B. Charnley, Maria N. Drozdovskaya, Sara Faggi, Davide Farnocchia, Aurélie Guilbert-Lepoutre, Marco Micheli, Nathan X. Roth, Megan E. Schwamb, Darryl Z. Seligman, Geronimo L. Villanueva
Astrophysics of Galaxies · Cross-listed from astro-ph.HE
Hydrodynamic Simulations of Eccentric Black Hole Encounters in AGN Discs
Andrew Imai, Henry Whitehead and Bence Kocsis
We investigate close encounters between stellar-mass black holes (BHs) in the gaseous discs of active galactic
nuclei (AGNs), during which binary black holes (BBHs) may form. We perform a suite of 483 2D adiabatic viscous hydrodynamic simulations within a shearing box prescription using the Eulerian grid code Athena++. We co-evolve the two embedded BHs with the gas. To probe the dependence of capture on non-circular initial conditions, we vary the initial radial separation $b$, the eccentricity $e$ of one of the stellar BHs around the central supermassive black hole, and the eccentric phase angle $\phi_e$. We consider eccentricities from $e=0$ to $e=0.1$ and compare them with the local disc aspect ratio $h=H/R_0\simeq0.005$. We find that small eccentricities shift the capture window in the parameter space. Eccentricities of order the disc aspect ratio, in particular $e\sim h$–$2h$, produce successful captures at initial separations that do not capture in the circular models. By contrast, systems with $e \gg h$ retain less gas before encounter and have lower capture fractions across the sampled parameter grid. We find that the first periapsis distance is a useful predictor of direct capture. Predicting direct capture for $r_{\rm p}<0.1r_H$ correctly classifies $92.7\%$ of Hill sphere encounters. The Hill sphere gas mass helps identify gas-poor failures, but provides no clear additional capture boundary within this suite, in which the initial disc density, temperature, and viscosity parameter are held fixed. Pre-encounter eccentricity modifies gas-assisted BBH formation through its combined effects on the first-encounter geometry and the gas reservoir available for orbital energy dissipation.
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Astrophysics of Galaxies
Galactic archaeology meets exoplanets: linking stellar birth radii to exoplanet demographics
M. L. L. Dantas, J. J. García-Delgado, I. Rebollido et al. (+1 more)
Stars observed in the solar vicinity were not necessarily born there. Radial mixing can redistribute stellar populations across the Galactic disc, decoupling their present-day locations from the environments in which they formed. We summarise a framework that combines Galactic chemical
evolution models with a generalised additive model to infer stellar birth radii. We apply it to 1327 predominantly thin-disc
planet hosts with homogeneous ages, Gaia DR3 astrometry, and SWEET-Cat atmospheric parameters. We find that giant-
planet systems preferentially trace metal-rich inner-disc birth environments, whereas rocky-only systems are less centrally concentrated; and no clear relation between radial displacement and detected
planet multiplicity.
Planet-host
stars that migrate towards the inner parts of the
Galaxy have systems with larger orbital separations; however, this may partly reflect the known dependence of planetary orbital properties on host-
star metallicity rather than a causal effect of Galactic stellar migration. These results illustrate how Galactic archaeology can complement
exoplanet demographics by linking planetary systems to their probable birth environments.
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All authors M. L. L. Dantas, J. J. García-Delgado, I. Rebollido, R. Smiljanic
Astrophysics of Galaxies · Cross-listed from astro-ph.SR
A census of massive eclipsing binaries in the Whirlpool Galaxy
Cheyanne Shariat, Kareem El-Badry, Maude Gull et al. (+3 more)
We present a census of massive eclipsing binary (EB) candidates in the Whirlpool
Galaxy (M51), a face-on spiral
galaxy at 7.5 Mpc with $Z\sim Z_\odot$. Using 34 epochs of red-optical Hubble Space
Telescope (HST) photometry and a single epoch of broadband UV-optical photometry, we identify 173 massive EB candidates ($>5~{\rm M_\odot}$) with orbital periods $P_{\rm orb}$=1-30 days. The sample traces young stellar populations across the spiral arms of M51. Joint light-curve and spectral energy distribution fits for 136 systems yield binaries spanning $T_{\rm eff}=10{,}000$-$50{,}000$ K, $R=7$-$66~{\rm R_\odot}$, and masses of $5$-$120~{\rm M_\odot}$. We use detailed injection-recovery simulations to quantify the survey's completeness and infer intrinsic properties of the massive binary population. At the population level, we infer a close-binary fraction of $f_{\rm close}=27.4\pm7.1\%$ for $2\leq P_{\rm orb}/{\rm d}<20$ and $0.1\leq q\leq1$. Over the same period range, the intrinsic period distribution is consistent with being log-uniform, ${\rm d}N/{\rm d}\log P_{\rm orb}\propto P_{\rm orb}^{\pi}$ with $\pi=0.29\pm0.32$. These demographics broadly match those of massive-
star populations in the Milky Way, LMC, and SMC, with tentative evidence for a lower close-binary fraction at lower
metallicity. Across the $\sim0.2$-$1.1~Z_\odot$ range spanned by these
galaxies, the overall similarities suggest that the formation of close massive binaries depends only weakly on
metallicity. Our survey establishes EBs as a powerful tool for measuring massive-binary demographics beyond the Local Group and provides a rich panchromatic census of $\sim$100,000 luminous
stars and variables in M51.
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All authors Cheyanne Shariat, Kareem El-Badry, Maude Gull, Daniel R. Weisz, Charlie Conroy, Alessandro Savino
Astrophysics of Galaxies
A model to mini-quench early galaxies by balancing stellar feedback and gas accretion
Judah Luberto and Steven R. Furlanetto
The James Webb Space
Telescope (JWST) has discovered a population of low-mass, early
galaxies with very low levels of
star formation over tens of Myr. These "mini-quenched"
galaxies were one of the many surprises from JWST and still require a robust explanation. We seek to explain a few important properties of these
galaxies, namely the timescales governing their
star formation and quenching. We use a simple model that pairs stellar feedback with the forces binding gas to a $z \sim 6$
galaxy, and with plausible parameter choices, this model produces mini-quenching in
galaxies approximately as large as observed mini-quenched
galaxies – up to total stellar masses of $\sim 10^{10} M_{\odot}$. In our model, the ejected interstellar gas forms into a spherical shell that expands outward during quenching. Our novel improvement is allowing this expanding shell to prevent accreting gas from falling in, in contrast to other models whose shells do not interact with accreting gas. Using our model, if a
galaxy accretes isotropically, we find that stellar feedback can reproduce observed timescales of mini-quenching with plausible
galaxy-formation parameter values. However, at low
halo masses, the quenching timescale of our model is too long ($> 100$ Myr). A potential solution for a long quenching time is for the
galaxy to accrete via filaments, in which case only a portion of the shell interacts with the accreting gas and the quenching timescale decreases to more accepted values. However, the ram pressure from feedback cannot stop filaments with very small opening angles, as occur in some
halo formation models, making mini-quenching impossible. Finally, we use this model to estimate the fraction of
galaxies undergoing mini-quenching, finding that it can be large.
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Astrophysics of Galaxies · Cross-listed from astro-ph.SR
The T-GEX project. II. Chrono-chemo-dynamic signatures of UV-bright FGK stars
D. Beltrán, M. L. L. Dantas, R. Smiljanic et al. (+1 more)
We compare the ages, chemical abundances, Galactic orbits, and inferred birth environments of 37 T-GEX
stars with strong (G1), normal (G2), and intermediate (G3) UV emission. The groups show distinct correlation structures: UV colours correlate with chemical and orbital quantities in G1; G2 has the largest number of significant (anti-)correlations; and no UV-colour correlation reaches the adopted threshold in G3. Most
stars have prograde disc-like orbits, while both
halo-like objects belong to G2. The groups overlap in the [Mg/Fe]-[Fe/H] plane, but G1 is shifted towards lower [Fe/H] and higher [Mg/Fe]. Among the 18 probable thin-disc members, G3 has a smaller median birth radius than G2 (5.70 versus 8.10 kpc), despite their nearly identical median guiding radii ($\langle R_g \rangle$; 8.23 versus 8.25 kpc). All five G1
stars are Ti-enriched compared to Fe, and four combine enhanced Co with comparatively low Mn and, in some cases, Cr. A related but less complete pattern occurs in G3, whereas Co enhancement in some G2
stars does not reproduce the joint signature. The UV-defined groups are heterogeneous and do not correspond to unique Galactic components. The convergence of $\alpha$-enhancement (likely thick disc members), positive Ti ratios, and the Cr-Mn-Fe-Co-Ni chemical abundance pattern (clearest in G1 but present in related form in G3) supports high-energy core-collapse (i.e. hypernovae) enrichment of the natal material of some UV-excess
stars. Additionally, the smaller G3 birth radii (for those in the Galactic thin disc) indicate more inward formation regions and provide a possible spatial link to UV-bright stellar populations in the bulges of spiral
galaxies. Neither result establishes a single causal pathway. Whether mixture-dependent metal-line blanketing connects this enrichment to the UV emission requires tailored spectral modelling.
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All authors D. Beltrán, M. L. L. Dantas, R. Smiljanic, P. B. Tissera
Astrophysics of Galaxies
A High-Mass Size Deficit for Void Galaxies in the Complete SDSS DR7
Olivia Curtis, Bryanne McDonough and Tereasa G. Brainerd
We characterize how environment shapes the sizes, luminosity functions, and mass functions of
galaxies in large-scale underdensities by comparing the NSA catalog of the Sloan Digital Sky Survey Data Release 7 with an identically selected TNG300 sample, both built with the void finding
algorithm VoidFinder, and by assigning a local average underdensity contrast to each
galaxy via a spherical top-hat smoothed density field approximation. Void
galaxies have fainter characteristic magnitudes than their non-void counterparts, and, at fixed stellar mass,
redshift, and color, NSA void
galaxies with $M_*>10^{11}h^{-1}M_\odot$ are about $11\pm3\%$ more compact than
galaxies in the field, a deficit the TNG300 simulation reproduces. The
galaxies that are responsible for this effect are almost all central and predominantly early type, i.e., the systems that are most likely to grow their outer envelopes via late-time mergers. These trends hold across two
redshift bins to $z\leq0.114$. Crucially, this deficit is not a fixed property of the void sample but a steep function of the underdensity contrast, deepening toward the emptiest interiors and washing out at a typical density, implying that strict density control and sample selection are imperative when conducting environmental dependency studies like these. The same environmental dependence appears in the stellar mass function, which shifts to lower masses in the deepest voids, and in the close-pair (i.e., the ongoing merger) fraction, which falls toward the emptiest regions. Together, these point to a late-time, merger-driven growth of massive
galaxies that is suppressed in voids, leaving their most massive members structurally distinct today.
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Astrophysics of Galaxies · Cross-listed from astro-ph.SR
Precise and Accurate Mass and Radius Measurements of Thirty Galactic Metal-Poor Stars in Detached Eclipsing Binaries
D. M. Rowan, K. Z. Stanek, C. S. Kochanek et al. (+4 more)
Detached eclipsing binaries have long served as fundamental
benchmarks for making direct comparisons with stellar models. By combining the light curve and radial velocity orbit of a detached eclipsing binary, precise masses and radii can be measured for both components. However, catalogs of eclipsing binaries are dominated by solar-
metallicity stars. Here we characterize fifteen eclipsing binaries selected to have $[\rm{M/H}]\lesssim -0.5$ using TESS photometry, Gaia XP spectra, large spectroscopic surveys, and Galactic kinematics. We use three spectrographs, PEPSI on the Large Binocular
Telescope, the Levy spectrograph on the Automated
Planet Finder
telescope, and CHIRON on the SMARTS 1.5m
telescope. We jointly model the light curves and radial velocities and measure the stellar masses and radii with median fractional uncertainties of < 1%. We use spectral disentangling to extract the spectra of both
stars and model them using the spectral synthesis code Korg. We find three systems with $[\rm{M/H}] < -2.0$, two of which are kinematically consistent with the Milky Way's
halo. J0001+2156 has $[\rm{M/H}]=-2.51$, making it the most metal-poor detached eclipsing binary characterized to date. Eleven of the twelve other systems have $[\rm{M/H}] \lesssim -0.5$ and are split between being highly ($[\alpha/\rm{M}] > 0.25$) and moderately ($[\alpha/\rm{M}] < 0.25$) $\alpha$-enhanced. We compare our measured masses and radii to predictions from theoretical isochrones and estimate the ages of the binaries. We estimate ages with typical uncertainties of $\lesssim 0.5$ Gyr, and three of the binaries have estimated ages greater than 10 Gyr, up to $13.8^{+0.8}_{-0.7}$ Gyr. Finally, we update the empirical relations for stellar masses and radii on the main sequence using a sample of 621
stars.
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All authors D. M. Rowan, K. Z. Stanek, C. S. Kochanek, Benjamin J. Fulton, Ilya Ilyin, Howard Isaacson, David V. Martin
Astrophysics of Galaxies
Rubin LSST DP2 unveils almost-dark galaxies in the Virgo Cluster
Minh Ngoc Le, Johan H. Knapen, Željko Ivezić et al. (+26 more)
Galaxies with the faintest surface brightness are currently known only in the Local Group. Similar objects should exist beyond our vicinity and are crucial for understanding
galaxy evolution, structure, and dark matter content, yet surveys have not reached the depth required to detect them systematically. We present a population of seven almost-dark
galaxies identified in Data Preview 2 of the Rubin Legacy Survey of Space and Time. They surround M49 in the vicinity of the Virgo Cluster, and exhibit central surface brightnesses in the range of $26.9 - 28.5 \, \mathrm{mag \, arcsec^{-2}}$ in the $g$-band, with half-light radii of $0.6 - 4.6 \, \mathrm{kpc}$ at the distance of Virgo, and stellar masses of $10^6 - 10^7 \, \mathrm{M_\odot}$. Their characteristics are analogous to those of the faintest and low-mass
galaxies identified among satellite
galaxies And XXI, And XXIII, and And XXV in the Local Group. This discovery demonstrates the power of the forthcoming Rubin LSST 10-year survey to uncover extremely faint
galaxies at scale, promising the large statistical samples needed to constrain the faint-end luminosity function and the nature of dark matter.
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All authors Minh Ngoc Le, Johan H. Knapen, Željko Ivezić, Junais, Aaron Watkins, Dan S. Taranu, Pierre-Alain Duc, Anthony Englert, Erfan Nourbakhsh, J. Anthony Tyson, Jiaxuan Li, Roberto J. Assef, Uzay Aydin, Jose Benavides, Natanael M. Cardoso, Priyanka Chakraborty, Ricardo Demarco, Bililign Dullo, Alister W. Graham, Marc Huertas-Company, Kian-Tat Lim, Jakub Nadolny, Dieu Nguyen, Reynier Peletier, Rossella Ragusa, Kevin Reil, R. Michael Rich, Hector Hernandez-Toledo, Michael H. F. Wilkinson
Astrophysics of Galaxies
Massive Galaxy Halos Contain Less Inner Dark Matter Than Predicted
Yu-Chen Wang, Yingjie Peng, Xiaohu Yang et al. (+17 more)
The mass profiles of
galaxy halos encode how baryons reshape dark matter distribution, yet direct observational constraints across the full radial range remain scarce. Here we combine stellar kinematics from MaNGA, H I dynamical measurements from ALFALFA, and independently calibrated
halo masses of SDSS groups to statistically reconstruct the mass distribution of central
galaxies over nearly two orders of magnitude in radius. We demonstrate that H I data alone do not provide reliable total
halo mass estimates, necessitating an independent group-based
halo-mass scale. Compared to the IllustrisTNG and EAGLE simulations, the observational profiles of low-mass
halos are broadly consistent; in contrast, massive observed
halos exhibit systematically lower dynamical masses at the H I radius, lower inner dark-matter masses, and lower central dark-matter fractions (about 4$\sigma$ difference in units of population scatter) at fixed total
halo mass. After subtracting baryonic contributions, the inferred dark-matter profiles remain broadly consistent with an NFW form, but with lower effective concentrations than predicted for massive
halos. These results suggest that the inner dark-matter content of massive
halos has been reduced more significantly than predicted by current hydrodynamical simulations, plausibly due to long-term baryonic
halo heating in massive systems.
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All authors Yu-Chen Wang, Yingjie Peng, Xiaohu Yang, Luis C. Ho, Dingyi Zhao, Jing Dou, Hao Fu, Zeyu Gao, Qiusheng Gu, Fangzhou Jiang, Yukun Liu, Roberto Maiolino, Houjun Mo, Canpo Su, Bitao Wang, Kai Wang, Bingxiao Xu, Feng Yuan, Kunyao Zhao, Xingye Zhu
Astrophysics of Galaxies
Rotational spectroscopy and astronomical search of propane-1-thiol (CH3CH2CH2SH) and propane-2-thiol ((CH3)2CHSH)
Wentao Song, Assimo Maris, Victor M. Rivilla et al. (+4 more)
This study focuses on propanethiol (or propyl mercaptan, C3H7SH), a sulfur analogue of propanol and a key target for investigating interstellar sulfur chemistry. We report the laboratory rotational spectroscopic characterization of its two structural isomers, propane-1-thiol (1PT) and propane-2-thiol (2PT). For 1PT, experimental analysis led to the observation of three almost isoenergetic conformers, Aa,Ag and Gg, marking the first-time report of the latter. For 2PT, both the anti and gauche conformers were identified. We also assigned, for the first time, several monosubstituted isotopologues in natural abundance: the 34S, 13C1, and 13C2 species for the anti-2PT conformer, as well as the 34S species for the gauche-2PT conformer.Resolvable tunneling splitting, caused by the large-amplitude motion of the sulfhydryl (SH) group, was observed for both the Ag-1PT and gauche-2PT conformers. Global fittings, integrating previous measurements, allowed for the accurate determination of rotational constants, quartic centrifugal distortion constants, and vibrational coupling parameters. The newly derived spectroscopic parameters were utilized to conduct an astronomical search toward the chemically rich Galactic Center molecular cloud G+0.693-0.027. While no evidence for propanethiol was found, we established rigorous upper limits for their column densities. These results indicate that 1PT and 2PT are approximately 13 and 5 times less abundant than ethanethiol in this source, respectively. Furthermore, the derived lower limit for the O/S ratio (29) for the 1-propanol/1-propanethiol pair is consistent with the solar value (37), proviiding a valuable
benchmark for understanding the depletion of sulfur in the ISM.
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All authors Wentao Song, Assimo Maris, Victor M. Rivilla, Miguel Sanz-Novo, Izaskun Jimenez-Serra, Luca Evangelisti, Sonia Melandri
Astrophysics of Galaxies · Cross-listed from astro-ph.SR
A large shell around the hypergiant VY Canis Majoris
D. P. K. Banerjee, V. Joshi, A. Evans A. A. Djupvik et al. (+10 more)
We report the detection of a remarkable shell around the red hypergiant VY CMa using data from the Spectro-Photometer for the History of the Universe, Epoch of Reionization, and Ices Explorer (SPHEREx). The shell, which in projection on the plane of the sky appears as a ring, is almost circular in appearance. It has an external diameter of $\sim14'$ to $15'$, and is seen most clearly in the SPHEREx 7827A spectro-photometric image. Filaments, radially aligned with VY CMa, are seen to cut across the shell in several places. We discuss the possibility that the shell is matter swept out from the neighboring
star forming region Sh 2-310, by the wind from VY CMa. Resonant atomic scattering, a light echo, or Extended Red Emission are explored as the source of the observed SPHEREx emission. However, no interpretation is without difficulty and further observations are most desirable.
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All authors D. P. K. Banerjee, V. Joshi, A. Evans A. A. Djupvik, Ken Hall, F.-J. Hambsch S. Sharma, G. Rangwal, A. Devaraj, T. R. Geballe, L. Izzo, T. Liimets, T. Schaeffer, S. Starrfield, C. E. Woodward
Astrophysics of Galaxies
CosmoDyn: a semi-analytic post-processing framework for the dynamical evolution of compact stellar systems and black holes in cosmological simulations
Pierre Boldrini, Paola Di Matteo, David Katz et al. (+5 more)
Although a large number of cosmological simulations are now publicly available, their spatial and mass resolutions remain insufficient to accurately follow the dynamics of compact stellar systems and black holes. A complementary approach is therefore required to exploit the cosmological assembly histories encoded in these simulations without rerunning them. We present CosmoDyn, an open-source Python framework that reconstructs time-dependent galactic environments from any cosmological simulations and explicitly follows unresolved compact objects within them. A distinctive feature of CosmoDyn is that it models not only the main host
galaxy but also its accreted satellites via moving gravitational potentials. The framework can therefore account simultaneously for the delivery of ex-situ populations and for the dynamical influence of satellites on in-situ population already present in the host. The modular pipeline comprises four main stages: reconstructing the evolving host and satellite potentials; generating in-situ and ex-situ populations of compact objects; integrating their orbits with configurable prescriptions for dynamical friction, and mass loss; and modeling tidal streams. Once reconstructed, the same cosmological environment can be reused to explore different objects, initial conditions, and physical prescriptions at low computational cost. CosmoDyn thus enables rapid parameter exploration and applications to statistically significant
galaxy samples, while its modular architecture is designed to incorporate progressively more realistic potentials, and formation models.
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All authors Pierre Boldrini, Paola Di Matteo, David Katz, Laia Casamiquela, Chervin Laporte, Maxime Assuerus, Marco Montuori, Glenn van de Ven
Astrophysics of Galaxies
CNO in Giant Metal-Poor Stars
Jannat Alazzawi
We present the chemical abundance analysis for elements carbon, nitrogen, oxygen and the carbon isotopic ratio in a sample of metal-poor
stars selected from the RAVE survey based on their extreme radial velocities. Stellar parameters were derived using Gaia photometry and parallaxes, and elemental abundances were determined from high-resolution UVES spectra obtained at the ESO Very Large
Telescope. The
stars span a wide
metallicity range (-2.9 ___ [Fe/H] ___ -1.2) and, for the majority of the sample, exhibit kinematic properties consistent with the Galactic outer
halo population.
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Astrophysics of Galaxies · Cross-listed from astro-ph.HE
Studying the Intermittency of Magnetized Interstellar Medium by Synchrotron Polarization Intensity and its Gradient
Ru-Yue Wang and Jian-Fu Zhang
Based on synthetic polarization observations, we qualitatively investigate the intermittency of the magnetized interstellar medium (ISM) through synchrotron polarization intensity (SPI) and synchrotron polarization gradient (SPG). Three principal findings emerge from our analysis: (1) The intermittency of the magnetized ISM is strongly modulated by magnetization and compressibility, with pronounced modulation effects predominantly observed in regimes characterized by strong magnetization and high compressibility. (2) The characterized intermittency of the magnetized ISM demonstrates a dependence on the electron spectral index under conditions where the random
magnetic field dominates. (3) SPG enables the identification of finer three-dimensional fractal structures in the case of strong Faraday depolarization. The synergistic application of SPI and SPG substantially enhances the reliability of probing magnetized ISM intermittency from real observations.
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Astrophysics of Galaxies
The Spitzer Data Fusion - A Far-Ultraviolet to Far-Infrared Multi-Wavelength Database in Spitzer Extragalactic Survey Fields
Mattia Vaccari
I present the Spitzer Data Fusion, a multi-wavelength photometric database providing far-ultraviolet to far-infrared flux measurements, together with photometric and spectroscopic
redshifts, for 4.4 million IRAC-selected sources over 65\,deg$^2$ in eight of the most widely studied extragalactic survey fields. A companion product, the SERVS Data Fusion, provides 2.8 million sources over 18\,deg$^2$ selected from deeper Spitzer warm-mission imaging. Catalogs are band-merged with wavelength-dependent matching radii, astrometrically registered against 2MASS, and distributed as FITS binary tables, one per field, as \href{https://doi.org/10.5281/zenodo.6120913}{DOI: 10.5281/zenodo.6120913} and as CDS/VizieR \href{https://cdsarc.cds.unistra.fr/viz-bin/cat/II/377}{catalog II/377}. The database is intended as a community resource for photometric
redshift calibration, spectral energy distribution fitting, sample selection and multi-wavelength cross-identification, and is a natural bridge between the Spitzer legacy fields and ongoing Euclid, Rubin and SKA precursor surveys.
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Astrophysics of Galaxies
Signatures of dark subhaloes in dwarf spheroidal galaxies: II. Transient and localised kinematic features
Eduardo Vitral, Jorge Penarrubia, Roeland P. van der Marel et al. (+1 more)
We use controlled N-body simulations to investigate whether dark matter subhaloes leave detectable signatures in the internal kinematics of dwarf spheroidal
galaxies. At each snapshot, we fit a velocity distribution function to stellar line-of-sight velocities and proper motions, construct normalised residual fields for the projected velocity components, and analyse their power-spectra. We show that subhalo encounters generate a plethora of kinematic features. Amongst the most prominent are rotation-like signals, which arise in our models even though the stellar component is initialised without intrinsic rotation. In line-of-sight velocity alone, several snapshots resemble the classical blueshift–
redshift pattern associated with stationary rotation. The plane-of-sky components, however, bring complexity, with alternating regions of expansion and contraction, as well as clockwise and anticlockwise streaming. Although we observe coherent streaming globally, these structures depart from typical
equilibrium configurations, while their residual power-spectra quantify the characteristic spatial scales involved. This signal strengthens in models containing more massive subhaloes and becomes difficult to recover for small stellar samples: robust power-spectrum recovery of the full velocity-space signature usually requires O(10^{4}) tracers, although a rotation signal alone can be recovered with considerably smaller samples. These results suggest that dwarf spheroidal velocity fields can retain signatures of subhalo heating. Future spectroscopy, improved Gaia astrometry, and chemo-dynamical information should turn these diagnostics into population-level probes of dark matter substructure.
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All authors Eduardo Vitral, Jorge Penarrubia, Roeland P. van der Marel, Matthew G. Walker
Astrophysics of Galaxies
Challenging the archetypal intermittent radio galaxy J0111+3906. New insights from optical GTC/OSIRIS and radio VLA and LOFAR observations
M. Orienti, J.A. Acosta-Pulido, E. De Rubeis et al. (+5 more)
We present results on new optical Gran Telescopio CANARIAS OSIRIS+ spectroscopy and
radio Very Large Array (VLA) observations at 360 MHz of the optical object behind the
radio emission 20 arcseconds east of the archetypal restarted compact symmetric object (CSO) J0111+3906. The optical counterpart is a post-starburst
galaxy at
redshift $z$ = 1.042, ruling out any physical relation between this object and the CSO
radio galaxy J0111+3906 at
redshift $z$ = 0.668. The
radio emission is therefore not the remnant of a past activity of the CSO J0111+3906 that took place around 10$^7$ years ago. When observed with the high angular resolution of VLA and the International LOw Frequency ARray
telescope the East
radio source is resolved in a compact component with spectral index 0.7, centred on the optical
galaxy, surrounded by diffuse emission with a slightly steeper spectrum. The upper limit to the radiative age of the East
radio source is a few million years. If the trigger of the
radio emission and the recent burst of
star formation observed in the East
radio source are causally connected, there must be a long time gap between the two phenomena. The multi-frequency analysis of the CSO
radio galaxy J0111+3906 pointed out excess flux density at 150 MHz, which may indicate the presence of fossil
plasma confined within the host
galaxy. In this scenario, the past activity of the CSO J0111+3906 switched off not long after its trigger, suggesting a duty cycle of about 10$^4$ yr.
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All authors M. Orienti, J.A. Acosta-Pulido, E. De Rubeis, C. Stanghellini, M. Bondi, F. D'Ammando, L. Coccato, I. Alemán-Martín
Astrophysics of Galaxies
Low Star Formation Efficiency in M31: Evidence for a Deficit of Bound Gas
Fangyuan Deng, Sihan Jiao, Hauyu Baobab Liu et al. (+14 more)
The Andromeda
galaxy (M31) exhibits a systematically low
star formation efficiency (SFE) compared to other
star-forming
galaxies.
Star formation is thought to be regulated by the mass of gravitationally bound gas. To investigate whether the low SFE in M31 originates from a scarcity of such bound gas, we analyze the dynamical state of its giant molecular cloud (GMC) population by estimating their virial parameters ($\alpha_{\rm vir}$). Using a JCMT-SCUBA2 850 micron dust-continuum GMC catalog as the parent sample, we combine it with IRAM 30 m CO(1-0) data to define a working sample of 173 GMCs and derive their kinematic properties. Most analyzed GMCs exhibit high $\alpha_{\rm vir}$, indicating that they are predominantly gravitationally unbound at the approximately 86 pc resolution of our observations. While no statistically significant global correlation is found between SFE and $\alpha_{\rm vir}$ for the full cloud sample, the upper
quantiles of the SFE distribution show progressively stronger negative trends with increasing $\alpha_{\rm vir}$. This upper-tail trend may arise from the combined effects of the virial parameter limiting the upper range of SFE values accessible to the GMC population and feedback-driven disruption reducing the number of high-SFE, high-$\alpha_{\rm vir}$ CO-bright clouds in the observed sample. The substantial scatter in the SFE-$\alpha_{\rm vir}$ plane likely reflects the diverse evolutionary stages of GMCs, the temporal mismatch between gas and
star formation tracers, and the limitations of a cloud-averaged virial parameter as a tracer of internal dynamical structure, making a simple one-to-one correspondence between $\alpha_{\rm vir}$ and instantaneous SFE difficult to recover for individual GMCs.
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All authors Fangyuan Deng, Sihan Jiao, Hauyu Baobab Liu, Jingwen Wu, Henrik Beuther, Fanyi Meng, Caroline Gieser, Yuxin Lin, Di Li, Chao-Wei Tsai, Junzhi Wang, Zhi-Yu Zhang, Fengwei Xu, Jakob den Brok, Linjing Feng, Zongnan Li, Yuxiang Liu
Astrophysics of Galaxies
Self-interacting dark matter delays bar growth in an isolated gas-rich galactic disk: torque-resolved numerical evidence
Dong-Biao kang
We investigate how a dynamically responsive gas disk changes the influence of self-interacting dark matter (SIDM) on stellar-bar formation. In an isolated Milky-Way-mass
galaxy with fixed total baryonic mass, the gas-rich collisionless (CDM) model develops a persistent bar at $1.96\,\Gyr$, whereas the matched SIDM model with $\sigmam=1\,\mathrm{cm^2\,g^{-1}}$ does so at $2.69\,\Gyr$. The final stellar $m=2$ amplitude is 0.437 in CDM and 0.340 in SIDM, a 22 per cent suppression; the corresponding gas-free controls remain weak over the same interval. An independently sampled gas-rich pair preserves the direction of both differences. Direct component-force measurements show that the SIDM stellar disk loses $2.82\times10^{11}\,\Msun\,\kpc\,\kms$ less angular momentum than its CDM counterpart. The integrated torque contrast is dominated by the dark
halo (approximately 74 per cent), with a substantial gas contribution (26 per cent), and is redistributed in radius and time rather than being a uniform reduction of
halo coupling. Conservation, force-accuracy, aperture, threshold, and independent-sampling checks support the ordering as a dynamical effect within this model. The result demonstrates that a live gas component can change both the sign and timing of the early SIDM impact inferred from collisionless disks, providing a mechanism-based constraint for future hydrodynamic SIDM studies.
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Astrophysics of Galaxies
The Delegate Survey: KOALA/AAOmega-IFU spectroscopy of three nearby dwarf galaxies
Kyungdo Ko, Helmut Jerjen, Sarah M. Sweet et al. (+6 more)
Assessing the cosmological typicality of the Local Group is crucial for establishing whether its dwarf
galaxy population is representative. To this end, the Delegate Survey targets dwarf
galaxies in Local Group analogues for systematic comparison. As a pilot study for the Delegate Survey, we obtained integral-field spectra of three dwarf
galaxies, GAMA 79098, GAMA 569709, and HIPASS J1159-19 S2, in two nearby
galaxy groups using the KOALA instrument on the AAT. The
galaxies were mapped at a spatial sampling of 1.25 arcsec per spaxel, providing two-dimensional spectral coverage of both the stellar and ionised gas components. Using continuum and emission-line maps, we investigate the ionisation structure,
star-forming properties,
metallicity,
star formation histories, and velocity fields of each system. GAMA 79098 exhibits properties closely analogous to the SMC, with ongoing
star formation superimposed on an old stellar population and moderate rotational support. GAMA 569709 resembles transition-type Local Group (LG) dwarfs such as NGC 147 and NGC 185, showing predominantly an old stellar population. HIPASS J1159-19 S2 is dominated by young
stars and intense
star-forming complexes, consistent with a dynamically young, gas-rich
galaxy group environment. The two GAMA dwarfs follow the LG stellar mass-
metallicity relation within uncertainties, while HIPASS J1159-19 S2 appears approximately 0.5 dex more metal-rich for its stellar mass. Overall, the structural, chemical, and kinematic properties of these dwarfs overlap substantially with analogous LG dwarfs.
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All authors Kyungdo Ko, Helmut Jerjen, Sarah M. Sweet, Ángel R. López-Sánchez, Simon Deeley, Caroline Foster, Holger Baumgardt, Pratyush Kumar Das, Adebusola Alabi
Astrophysics of Galaxies · Cross-listed from astro-ph.CO
Void probability function in the Quijote simulations
Snehasish Bhattacharjee
The void probability function (VPF) is the likelihood of finding no tracers (
galaxies or dark-matter
haloes) within a given volume and is sensitive to the large-scale matter distribution. We investigate the VPF of dark matter
haloes and
galaxies using the Quijote N-body simulations across a range of cosmological models, including $\Lambda$CDM and several extensions. We examine its dependence on cosmology,
redshift,
halo mass, morphology, and sample dilution, and compare the results with theoretical predictions from the
geometric hierarchical (GH) and negative binomial (NB) models. We find that the
halo VPF is sensitive to cosmology and
halo mass and follows the GH model at $z=0$, with $\Lambda$CDM showing the smallest deviation and the massive-
neutrino cosmology the largest. At higher
redshift and stronger sample dilution, the VPF departs from the GH model and approaches the NB model. The dependence on
halo mass varies with cosmology, with low-mass
haloes showing the largest deviations in $\Lambda$CDM, while intermediate- and high-mass
haloes show stronger deviations in the modified-
gravity scenario. In
redshift space, the VPF shifts toward the NB model, with primordial non-Gaussianity producing the largest deviations. For
galaxies, the VPF depends on morphology and cosmology, with ellipticals following the GH model and spirals following the NB model. We also find that
cosmic variance introduces non-negligible scatter in the VPF measurements. Overall, these results suggest that the VPF could be useful as a computationally efficient probe to distinguish extensions of the standard $\Lambda$CDM model in upcoming large-volume
galaxy surveys.
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Astrophysics of Galaxies · Cross-listed from astro-ph.HE
RadioAstron space-VLBI imaging of the jet in M87: II. The parsec-scale structure at 4.8 GHz
Evgeniya V. Kravchenko, Tuomas Savolainen, Alexey S. Nikonov et al. (+9 more)
We present RadioAstron observations of the M87 jet obtained on 2014 February 4-5 at 4.8 GHz ($\lambda=6.2$ cm). The correlated signals between the 10-m space
antenna and ground-based
radio telescopes were detected up to projected baselines of $\thicksim3$\,Earth diameters (0.65~G$\lambda$). The orientation of the jet downstream of the core shifts northward, consistent with the long-term oscillating trend reported in other studies. An elliptical body mode of the Kelvin-Helmholtz instability can create the observed helical shape of the jet. The estimated wavelength of this instability mode suggests that its origin may be related to some processes in the
accretion disc. We present 1.7 - 4.8 GHz and 4.8 - 15.4 GHz spectral index maps showing flattening of the spectrum along the outer streamlines and along the jet spine. Simulations and analysis show that this spectral flattening is partially artificial and is a common systematic effect of the CLEAN procedure of VLBI imaging. The spectral index of the M87 jet is consistent with the optically thin emission, while its steepening can be produced by the propagation of the instability modes causing higher pressure regions near the jet boundary and in its interior.
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All authors Evgeniya V. Kravchenko, Tuomas Savolainen, Alexey S. Nikonov, Ilya N. Pashchenko, Elena E. Nokhrina, Petr A. Voitsik, Leonid I. Gurvits, Yuri Y. Kovalev, Jae-Young Kim, Mikhail M. Lisakov, Andrei P. Lobanov, Kirill V. Sokolovsky
Astrophysics of Galaxies
Galaxy-Galaxy Strong Lensing simulation with the GPU acceleration across surveys and multi-bands
Fucheng Zhong, Ruibiao Luo, Nicola R.Napolitano et al. (+3 more)
We present a GPU-accelerated, PyTorch tensor-based simulation framework designed to generate high-fidelity
galaxy-
galaxy strong
lensing images. By integrating synthetic Spectral Energy Distribution (SEDs), the pipeline accurately models the
redshift-dependent photometric properties of lens and source
galaxies, ensuring physical consistency across multi-band observations. The framework incorporates key observational parameters, including Point Spread Functions (PSF), magnitude limits, and zero points, to replicate specific survey conditions, thereby enabling robust cross-survey joint analyses. As an application, we simulate multi-band images for KiDS, LSST, and Euclid using identical lens model parameters, and employ a deep learning network to evaluate image deblending performance. In particular, the simulation leverages PyTorch to ensure full auto-differentiability and GPU acceleration, making it a highly efficient tool for advanced deep learning
algorithms that require gradient-based optimization beyond standard model training. Our framework achieves a speedup of approximately $\mathcal{O}(10^3)$ over traditional CPU-based pipelines, demonstrating the potential feasibility of joint gradient-based lens modeling across next-generation surveys.
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All authors Fucheng Zhong, Ruibiao Luo, Nicola R.Napolitano, Crescenzo Tortora, Valerio Busillo, Rui Li
Astrophysics of Galaxies
A Detailed GASKAP-HI View of Shells and Loops in the Magellanic Bridge
Shin-Jeong Kim, Antoine Marchal, N. M. McClure-Griffiths et al. (+19 more)
We present 8 pc-scale GASKAP-HI observations of an HI shell (diameter \sim130 pc) associated with the H\alpha shell DEM171 in the Magellanic Bridge. The Bridge's diffuse, HI-dominated environment, with minimal galactic shearing and fewer overlapping
star-forming regions, provides an ideal environment to study cold gas formation driven by stellar feedback. To investigate the HI multi-phase structure and kinematics of the shell, we perform Gaussian decomposition of HI line profiles. We identify cold HI components with velocity dispersions \sigma < 2.5 km/s located within the shell. Complementary Herschel far-infrared (FIR) 250\micron and H\alpha maps show that while the central cavity is ionized, the shell walls contain cold HI, molecular gas, and dust, suggesting that stellar feedback has promoted cold gas formation or swept pre-existing cold gas into the shell walls. We also identify cold HI clumps outside the shell tracing a larger-scale structure, MB-Loop I. To investigate the large-scale context, we apply a
Fourier transform method to HI emission-line profiles to map the lower limit of cold-gas column densities across a section of the Bridge, revealing structures from large loops to smaller shells. The association between MB-Loop I and the HI shell suggests that cold HI gas may pre-exist before shell expansion. Finally, the shell exhibits asymmetric expansion, with a preferred orientation roughly perpendicular to the arc along MB-Loop I. Our results show that cold HI gas exists across a wide range of spatial scales in the Magellanic Bridge, highlighting the dynamic interplay that shapes the surrounding interstellar medium.
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All authors Shin-Jeong Kim, Antoine Marchal, N. M. McClure-Griffiths, J. R. Dawson, James Dempsey, Helga Dénes, John M. Dickey, Steven J. Gibson, Katie Jameson, Ian Kemp, Bumhyun Lee, Min-Young Lee, Adam K. Leroy, Callum Lynn, Yik Ki Ma, Marc-Antoine Miville-Deschênes, Eric G. M. Muller, Claire Murray, Hiep Nguyen, Nickolas Pingel, Hye-Jin Park, Jacco Th. van Loon
Astrophysics of Galaxies
A Possible Hidden Hot Halo Component Revealed by Joint X-ray and Sunyaev–Zel'dovich Observations
Jiang-Tao Li, Rui Huang, Joel N. Bregman et al. (+2 more)
Massive
galaxies are expected to host extended
halos of hot gas that contain a substantial fraction of their baryons and feedback energy. X-ray observations probe the dense, X-ray-bright component of this circumgalactic medium (CGM), while the thermal Sunyaev-Zel'dovich (SZ) effect is also sensitive to lower-density gas through its integrated thermal pressure. We present the first spatially resolved joint X-ray and SZ analysis of a massive isolated disk
galaxy, using deep XMM-Newton observations of NGC 4594 from the X-raying the
Accretion Reservoir Transferred to the ATmosphere Orbiting a Massive Spiral (XART-ATOMS) program, together with multiple independent Planck-based SZ reconstructions. The measured SZ signal in the inner
halo appears to exceed the value predicted from the X-ray-derived gas properties, even after accounting for major systematic uncertainties. Our preferred interpretation is that an additional lower-density CGM component contributes little to the observed soft X-ray emission but carries substantial thermal pressure. Under a simple two-phase model in approximate pressure
equilibrium, the most probable X-ray-to-SZ ratio implies that the detected X-ray-emitting gas occupies only a small fraction of the
halo volume, with a characteristic filling factor of f_X ~ (4-6)x10^-3 near r~50 kpc. Such a small filling factor implies that single-phase X-ray analyses can underestimate the baryon mass contained in the hot CGM by a factor of ~2.5, while the thermal energy content of the CGM is underestimated by about one order of magnitude. The non-detection of the additional component in the X-ray spectra requires it to be very hot and/or spatially extended, so weak in the soft X-ray emissions. These results favor the presence of a "hidden" X-ray-faint hotter
halo component, while alternative interpretations, including a nonthermal contribution, are not excluded.
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All authors Jiang-Tao Li, Rui Huang, Joel N. Bregman, Q. Daniel Wang, Cameron Pratt
Astrophysics of Galaxies
Does galaxy-scale compactness regulate nebular electron density? A cross-scale test with DESI
Shihong Liu and Yu Rong
Nebular electron density, $n_e$, traces ionized gas in small-scale H\,ii regions and diffuse ionized structures, whereas
galaxy stellar surface density, $\Sigma_\star$, measures compactness on kpc scales. Whether these quantities are correlated is therefore a cross-scale question rather than a geometrical identity. We test whether nebular electron density varies systematically with
galaxy-scale stellar compactness after controlling for the correlated effects of stellar mass and
star-formation rate (SFR). We use DESI DR 1 spectra to test this cross-scale connection in AGN-clean
star-forming
galaxies at $0.10<z<0.44$. We divide each
redshift interval into tertiles of $\Sigma_\star=M_\star/(2\pi R_e^2)$. We construct one controlled sample in which the $M_\star$ distributions are matched across the three compactness tertiles, and a second in which their joint $M_\star$–SFR distributions are matched, thereby minimizing the influence of these correlated
galaxy properties. For each compactness tertile, we stack the
galaxy spectra with equal weight and use the stacked spectrum to measure the average $n_e$ of the
galaxies in that sample. The average $n_e$ increases systematically toward higher stellar surface density in all
redshift intervals. This is the first controlled population-level evidence for a correlation between kpc-scale
galaxy stellar surface density (compactness) and the average $n_e$ of ionized gas on subgalactic scales. Its persistence after matching both $M_\star$ and SFR suggests that a more compact stellar configuration may promote higher gas pressure and/or stronger confinement of ionized gas, linking
galaxy-scale structure to nebular conditions.
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