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Physics Astrophysics Astrophysics of Galaxies

astro-ph.GA Watch Astrophysics of Galaxies

Friday 2 October

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

Baryonic Imprints on DM Halos: characterizing the full concentration-mass probability distribution with CAMELS

Elisa J. Gao and Dhayaa Anbajagane

The halo concentration, which represents the distribution of matter within a halo, is a vital tool for modeling the matter distribution on scales ranging from megaparsecs to sub-kiloparsecs. While significant progress has been made on connecting the impact of astrophysics on the mean concentration as a function of halo mass, the same connection to higher moments of the concentration distribution remains far less explored. We employ the IllustrisTNG runs in the CAMELS simulation suite to simultaneously quantify the astrophysics and cosmology dependence of the first four moments of the concentration-mass relation; the mean, the scatter, the skewness, and the kurtosis. We use normalizing flows to model the concentration distribution as a function of halo mass, redshift, and six cosmological/astrophysical parameters. We focus on the mass range $M_{\rm vir} \in [10^{11}, 10^{14.5}] M_{\odot}/h$, and the redshift range $z \in [0, 1]$. All higher-order moments exhibit a mass-dependent sensitivity to both astrophysics and cosmology. The behavior in dark matter-only simulations follows the known effects of active mergers and of tidal stripping in smaller halos. Once galaxy formation is included, the scatter shows non-monotonic behavior at the Milky Way (MW) mass-scale, and the amplitude of this behavior is strongly influenced by the baryon fraction and supernovae (SNe) feedback parameters. The skewness has a large sensitivity to the baryon fraction as well and is mostly insensitive to the other parameters, while the kurtosis follows the behavior set by the skewness. Results for the ASTRID simulation suite show similar behavior as that of IllustrisTNG. The cosmology and astrophysics dependence of these higher-order moments impact analyses that are sensitive to the full distribution of the concentration-mass relation, particularly for halos at/below the MW mass scale.
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Astrophysics of Galaxies

The differences in the Narrow Line Region of nearby QSOs 1 and QSOs 2: II - Signatures of kinetic feedback

Gabriel R. Hauschild-Roier, Thaisa Storchi-Bergmann, Rogério Riffel et al. (+2 more)

We compare the integrated kinematic properties of the Narrow-Line Region (NLR) of ~1500 type 1 and ~700 type 2 QSOs at 0.4 < z < 0.5 using emission-line profiles from SDSS-IV spectra. The NLR [OIII] 5007 and Hbeta emission lines are fitted using a two-component model comprising a narrow (v_n, sigma_n) and a broad component (v_b, sigma_b), while fainter lines are fitted with a single Gaussian component. Both QSO types exhibit similar median narrow-component velocities (v_n ~ 0) and velocity dispersions (sigma < 200 km s^-1), consistent with motion driven by the host galaxy's gravitational potential. However, parameters associated with the broad, high-velocity gas component (v_b, v_05, v_10, v_[NeV], sigma_b, W80 and W90) differ: QSOs 1 display larger blueshifts and broader emission lines than QSOs 2. This suggests that these components trace Active Galactic Nuclei (AGN) outflows, that appear stronger in QSOs 1, leading to higher estimated mass-outflow rates (\dot{M}_out) and kinetic powers (\dot{{E}_out). Rather than offering absolute determinations of \dot{M}_out and \dot{E}_out – which remain subject to physical uncertainties – this statistical study supports the higher NLR excitation found for QSOs 1 in Paper I, as an orientation effect: in QSOs 1, we observe gas closer to the AGN core, where velocities and velocity dispersions are intrinsically higher. Nevertheless, the trend of QSOs 2 exhibiting higher average [OIII] luminosities than QSOs 1 suggests an evolutionary contribution, where QSOs 2 represent an early obscured AGN phase followed by a blowout phase that reveals the central core as a QSO 1.
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All authors Gabriel R. Hauschild-Roier, Thaisa Storchi-Bergmann, Rogério Riffel, Vincenzo Mainieri, Lara Gatto

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

The Virgo Cluster as a Case Study for Ancient Cosmic Ray Halos in Radio and X-rays

Philip F. Hopkins, Emily M. Silich, Jack Sayers et al. (+2 more)

Virgo is the nearest cool core (CC) galaxy cluster, and is archetypal of the class of X-ray weak CCs. Despite the X-ray continuum implying a large cooling rate ($\gtrsim 10\,{\rm M_{\odot}\,yr^{-1}}$), measurements of cooler gas phases, dust, and star formation show almost no cooling outside the M87 nucleus. It is also known that M87$^{\ast}$ is a prodigious source of cosmic ray (CR) leptons observed in radio and $\gamma$-rays, and recent radio observations have shown that the M87 radio halo is low-frequency and its spectral index steepens rapidly away from the injection region+jets, consistent with an aging, low-energy CR population. We demonstrate that coupling X-ray and radio to newer Faraday rotation limits on the magnetic field, this implies the CRs within the CC radius ($\lesssim 40$kpc) must contribute significantly to the total pressure and soft X-ray emission, through a combination of Coulomb heating the gas and inverse-Compton (IC) scattering microwave background photons to $\sim$keV. We show this can explain the apparent correspondence between jet/radio power and X-ray cooling luminosity, and why the X-ray inferred cooling rate appears much larger than otherwise observed. This would also explain why the central X-ray inferred metallicity at $\lesssim 10\,$kpc appears to be suppressed relative to the UV/optical inferred metallicity (in a wavelength-dependent manner). Compared to more extreme radio+X-ray sources like Perseus, we find the observations require a softer 'escaping' CR spectrum (escaping or accelerated outside $\gtrsim 1\,$kpc from M87$^{\ast}$).
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All authors Philip F. Hopkins, Emily M. Silich, Jack Sayers, Sam B. Ponnada, Isabel S. Sands

Astrophysics of Galaxies

Internal Radiative Feedback Triggers Global Collapse and Direct-Collapse Black Hole Formation in Metal-free Atomic-Cooling Haloes

Masaki Kiyuna, Sunmyon Chon, Kazuyuki Omukai et al. (+1 more)

The formation of heavy seed black holes from the collapse of supermassive stars (SMSs) is a promising pathway to the supermassive black holes (SMBHs). In the conventional direct-collapse scenario, however, SMS formation requires an extremely strong external far-ultraviolet (FUV) field to suppress H$_2$ cooling and fragmentation. Here, we use cosmological radiation-hydrodynamic simulations to show that SMSs can form in metal-free atomic-cooling haloes even under subcritical FUV backgrounds with $J_{21}=1$-$10^2$. We follow the evolution for $\sim1$-$2~{\rm Myr}$ after the onset of star formation, including FUV and ionizing radiation from stars formed within the halo. Star formation proceeds through a characteristic two-stage evolution. H$_2$ cooling initially induces fragmentation and the formation of ordinary Pop III stars. Internal FUV radiation from these stars then photodissociates H$_2$ and suppresses further fragmentation, while the surrounding warm gas reservoir contracts under self-gravity and undergoes global collapse through atomic cooling. This collapse drives inflow rates of $\sim0.1$-$1~{\rm M_\odot~yr^{-1}}$ and produces rapidly accreting protostars that reach $\sim2$-$6\times10^4~{\rm M_\odot}$ by the simulations end. Since rapid accretion is still ongoing, these objects are expected to grow to $\sim10^5~{\rm M_\odot}$ SMSs and then form direct-collapse black holes (DCBHs). The global collapse is accompanied by clustered star formation, producing a compact, top-heavy stellar system around the SMSs. The estimated DCBH abundance, $n_{\rm DCBH}\sim10^{-3}$-$10^{-2}~{\rm cMpc^{-3}}$, is high enough to provide a plausible progenitor population for Little Red Dots and present-day SMBHs. Our results demonstrate that internal stellar feedback can trigger, rather than prevent, SMS formation, substantially relaxing the external FUV requirement for heavy-seed formation.
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All authors Masaki Kiyuna, Sunmyon Chon, Kazuyuki Omukai, Raffaella Schneider

Astrophysics of Galaxies

SCALES. II. The Internal Composition of Giant Star-Forming Clumps at $z = 1 - 4$

Boris S. Kalita, Adélaïde Claeyssens, Luis C. Ho et al. (+12 more)

Star-forming structures of scale $\sim0.5-1\,\mathrm{kpc}$, dubbed 'giant' star-forming clumps, are routinely detected in unlensed surveys of $z > 1$ galaxies. Two scenarios are usually invoked to explain their existence – genuine physical structures or resolution-driven artifacts – yet distinguishing between them requires characterizing their internal structure. In this work, part of the Star-Forming Clumps As Layered Emergent Structures (SCALES) series, we hence ask: What is inside a giant clump? We analyze 23 lensed galaxies at $z=1-4$ with JWST/NIRCam using difference-of-Gaussian decomposition to model (lensed) clumps at $\sim 100-300\,\mathrm{pc}$ scales, and the surrounding extended component (EC) at giant clump scales. Associating clumps to ECs, we effectively identify 44 giant clumps. Characterizing giant clump stellar mass composition using the most massive member clump and the remaining constituent clumps, we find it consistent with random sampling of the host galaxy's clump population, and hence the clump stellar mass function. This conclusion agrees qualitatively with both prevailing scenarios – (I) dominant long-lived giant clumps, although requiring constant renewal of their constituents, and (II) giant clumps as mere blended clump associations. However, most models make no strong claims about their internal mass distribution beyond order-of-magnitude statements, and our observations thus provide an empirical constraint against which such models can be re-evaluated. Finally, using the total mass budget of clumps and ECs, we find that the clump stellar mass function cannot be described by a single power law of slope $\approx 2$, but requires a break to a shallower slope at $\sim 10^{7.4}\,\mathrm{M_{\odot}}$.
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All authors Boris S. Kalita, Adélaïde Claeyssens, Luis C. Ho, Miroslava Dessauges-Zavadsky, Natascha M. Förster Schreiber, Emanuele Daddi, John D. Silverman, Naval Kishor Bhadari, Changhao Chen, Fangzhou Jiang, Ke Wang, Jinning Liang, Alvaro Segovia Otero, Jinyi Shangguan, Francesco Sinigaglia

Astrophysics of Galaxies

SCALES. I. Bridging Lensed Clump - Giant Clump Scales in Lensed Galaxies at $z=1-4$

Boris S. Kalita, Adélaïde Claeyssens, Luis C. Ho et al. (+12 more)

Dense star-forming regions in $z>1$ galaxies, often termed 'clumps', have been studied across two distinct regimes of telescope resolution, each motivating interpretations in tension with the other. In the SCALES series (Star-Forming Clumps As Layered Emergent Structures), we aim to connect star-forming structures across scales, from the $\sim100\,\mathrm{pc}$ clumps in lensed studies to the $\sim\mathrm{kpc}$-scale ”giant” clumps in unlensed surveys. In this first paper, we present a difference-of-Gaussian (DoG) decomposition that simultaneously models $\sim100-300\,\mathrm{pc}$ (lensed) clumps and $\sim\mathrm{kpc}$-scale component (the extended component, or EC), which would together constitute the giant clumps seen at lower resolution. Here the EC is treated as a scale-separated local background rather than a physical object, absorbing all light that is not a compact clump. Applying this to 23 moderately lensed ($\mu \approx 2-9$) galaxies at $z_{spec} = 1-4$ to evaluate clump properties (deferring ECs and giant clumps to the next work), we find their stellar mass to be capped at $\sim 10^{8.5}\,M_{\odot}$. We measure clump stellar mass function slope of $2.19 \pm 0.06$, which is higher than typical, and may reflect a physical truncation at the massive end. We also show that empirical correlations of clump surface densities and clump-to-host mass ratio with redshift are exaggerated by redshift-dependent detection bias, so $\sim100-300\,\mathrm{pc}$ clumps are largely co-similar across our range ($z = 1-4$). Finally, combining clump mass, size and age estimates with literature gas-dispersion measurements at similar scales, we argue that $\sim100\,\mathrm{pc}$ clumps are themselves composed of star-cluster-like sub-components at much smaller scales.
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All authors Boris S. Kalita, Adélaïde Claeyssens, Luis C. Ho, Miroslava Dessauges-Zavadsky, Natascha M. Förster Schreiber, Emanuele Daddi, John D. Silverman, Naval Kishor Bhadari, Changhao Chen, Fangzhou Jiang, Ke Wang, Jinning Liang, Alvaro Segovia Otero, Jinyi Shangguan, Francesco Sinigaglia

Astrophysics of Galaxies

Searching for Green Pea Galaxies in the SFACT Survey

Kristin N. Baker, John J. Salzer, Brooke Kimsey-Miller et al. (+5 more)

Green Pea galaxies (GPs) are a class of rare, extreme star-forming galaxies whose physical properties closely resemble high-redshift Ly-{\alpha} emitting galaxies. Their high equivalent width [O III] emission lines make them readily identifiable in surveys of emission-line galaxies like the on-going deep, narrowband Star Formation Across Cosmic Times (SFACT) survey. In this study, we use broadband gri colors and [O III] equivalent widths derived from narrowband images to select a new sample of ~120 GP candidates from a catalog of [O III]-detected galaxies identified in the SFACT survey. All SFACT GP candidates have spectroscopically confirmed redshift in the range z = 0.31-0.51. The median apparent magnitude of our sample is g = 22.9. We compare the properties of our GP candidate sample to other samples of known GPs. We find that the excellent depth of SFACT allows us to detect GP candidates to lower luminosities than these comparison samples. This is the first catalog of SFACT GP candidates; additional candidates will be added as the spectroscopic follow-up of the SFACT survey is completed.
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All authors Kristin N. Baker, John J. Salzer, Brooke Kimsey-Miller, Samantha W. Brunker, David J. Carr, Jennifer Sieben, Steven Janowiecki, Samir Salim

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

Baryonic Imprints on DM Halos: the concentration-mass relation and its dependence on 28 model parameters in the CAMELS suite

Cami Delgado and Dhayaa Anbajagane

The evolution of baryons in halos, as well as their gravitational impact on the total-matter phase space, has a rich phenomenology and is vital in answering many questions in both cosmology and astrophysics. We use the CAMELS simulation suite to quantify the impact of twenty-three different galaxy formation parameters/processes (as well as five cosmological parameters) on the concentration–mass relation, $c_{\rm vir}$ - $M_{\rm vir}$, which characterizes the radial density distribution in halos. We construct a simulation-informed nonlinear model for concentration as a function of halo mass, redshift, and twenty-eight cosmological/astrophysical parameters. This is done using 2048 simulations of the IllustrisTNG galaxy formation model from the CAMELS suite. We extract the imprints of galaxy formation across a wide range in mass $M_{\rm vir} \in [10^{11}, 10^{14.5}]$ $M_{\odot}/h$ and in redshift $z \in [0, 3]$, finding clear mass- and redshift-dependent features in each of the different feedback mechanisms. From our measurements, we construct a three-component phenomenological model that can include astrophysical imprints in the concentration–mass relation in a fast and simple manner.
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Astrophysics of Galaxies

A multi-scale view of molecular gas and magnetic fields in the Antennae galaxies

Akhil Lasrado, Enrique Lopez-Rodriguez, Claudia Cicone et al. (+5 more)

Major mergers are transformative events in galaxy evolution, dynamically reshaping the stellar and gas makeup of the hosts, as well as the galaxy-scale magnetic fields (B-fields) that permeate their interstellar medium (ISM), altering both B-field strength and configuration. In this work, we study in detail the link between the co-evolving gas and B-fields in the cold ISM phase of the nearby Antennae galaxy merger (NGC 4038/4039), using CO(3-2) data from the LAsMA receiver at the APEX telescope and ALMA, together with archival 154 $\mu$m dust polarization data from the SOFIA/HAWC+. We characterize trends between measurements of molecular gas intensity and velocity dispersion with polarization measurements at kpc-scales with the APEX and SOFIA data. We find anti-correlations with CO intensity ($\rho\lesssim-0.6$) and CO velocity dispersion ($\rho\lesssim-0.4$), which are signposts of geometric depolarization. Since dust polarization measurements are a density-weighted line-of-sight integrated average of B-field vectors below the beam size, the ALMA data can serve as a proxy of density structures below the SOFIA beam on a channel-by-channel basis. Through a geometric analysis of structures in the ALMA channels, we identify salient kinematic features in the overlap region strongly aligned with the SOFIA-inferred B-field orientation. This indicates that these kinematic features might dominantly lend their orientation to the measured field direction, assuming a correspondence between molecular gas structures and galactic B-fields, owing to their density or high polarization fraction. We also identify a modest trend ($\rho\sim0.5$) between the coherence of the molecular gas, a proxy of the line-of-sight angular dispersion, at small scales, and the SOFIA polarization fraction, showing that the polarization fraction measured at $\sim2$ kpc scales is sensitive to structures at $\sim50$ pc scales.
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All authors Akhil Lasrado, Enrique Lopez-Rodriguez, Claudia Cicone, Axel Weiss, Andreas Lundgren, Boy Lankhaar, Robert Wissing, Sijing Shen

Astrophysics of Galaxies

Discovery of thermal radio recombination line emission toward the high-mass protostar IRAS18162$-$2048

R. Fedriani, J.F. Gomez, Y. Cheng et al. (+7 more)

The physical conditions within the innermost few tens of au of high-mass protostars ($M_*>8~M_\odot$) remain largely unexplored. At these scales, ionised emission may trace photoionised gas, accretion disks, or the base of protostellar jets. We search for ionised emission in the form of radio recombination lines (RRLs) in high-mass star-forming regions. We use archival data from the Atacama Millimeter/submillimeter Array (ALMA) interferometer in band 6 ($\sim$1.3 mm) with a resolution of $\theta_\mathrm{beam}\sim53~\mathrm{mas}\times42~\mathrm{mas}$ to examine the high-mass protostar IRAS18162$-$2048, driving source of the Herbig-Haro (HH) objects HH80-81. We detect, for the first time in this protostar, the thermal emission of the RRL H30$\alpha$ ($\mathrm{rest~frequency}=231.90093$ GHz). The ionised emission is spatially unresolved in our observations, but we estimate an emitting region $\lesssim50$ au at the source distance of 1.4 kpc. The H30$\alpha$ line profile is broad and spectrally resolved with a Local Standard of Rest velocity of $\sim-14~\mathrm{km~s^{-1}}$ (i.e., $\sim-26~\mathrm{km~s^{-1}}$ blue-shifted with respect to the systemic velocity of the cloud) and a full width at half maximum of $\sim82~\mathrm{km~s^{-1}}$. These observations suggest that the H30$\alpha$ line is tracing outflowing blue-shifted material in the well-known radio jet from this object. This detection opens the possibility of detailed studies of the kinematics and physical properties of ionised jets.
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All authors R. Fedriani, J.F. Gomez, Y. Cheng, M. Osorio, G. Anglada, C-Y. Law, J.M. Masque, A.F. Placinta-Mitrea, G. Blazquez-Calero, G. Cosentino

Astrophysics of Galaxies

Merger remnant in TXS 1033+026 - I: $\rm H\alpha$ and HI 21-cm observations suggest counter-rotating gas

J. N. H. S. Aditya, Hyein Yoon, L. G. Dahmer-Hahn et al. (+5 more)

We conducted eMERLIN and Gemini integral field unit (IFU) observations towards TXS 1033+026, a post-merger ultraluminous infrared galaxy, to study the radio continuum and $\rm H\alpha$ and HI 21 cm lines at sub-kiloparsec scales. We find a symmetric, two-sided core- jet structure in both L-($\approx 1.4$ GHz) and C-($\approx 4.8$ GHz) band continuum images. The active galactic nucleus likely has a double-double radio morphology, indicating possible multiple episodes of activity. The Gemini IFU observations provided sub-arcsecond resolution. Results from these observations suggest the presence of a kiloparsec-scale circumnuclear, warped $\rm H\alpha$ disc that rotates around the core. The HI 21 cm maps reveal a complex kinematic structure, with indications of two counter-rotating gas components orbiting the core-jet axis; one of these components counter-rotates relative to the kiloparsec-scale $\rm H\alpha$ disc. However, the true morphology of this structure may be more complex than our interpretation suggests. We estimate a HI 21 cm velocity-integrated optical depth of $\rm 90 \pm 3 \ km \ s^{-1}$. We note that these are the first results to probe $\rm H\alpha$ and cold neutral hydrogen gas in TXS 1033+026 at sub-kiloparsec scales.
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All authors J. N. H. S. Aditya, Hyein Yoon, L. G. Dahmer-Hahn, Renzhi Su, Rajeshwari Dutta, Xiaolong Yang, Elaine Sadler, Matthew T. Whiting

Astrophysics of Galaxies

A two-stage settling of the Milky Way disk revealed by precise ChronoGal ages

David Mirabal, Carme Gallart, Tomás Ruiz-Lara et al. (+9 more)

The spatial distribution of Galactic disk stars of different ages and metallicities encodes its dynamical evolution history and formation pathways. The lack of precise ages for large, representative samples of stars has traditionally been a drawback for securely differentiating among formation scenarios proposed to explain the vertical properties of the Milky Way disk (e.g. upside-down formation versus secular dynamical heating). In this Letter, we use CMD-fitting of Gaia data to derive very precise age-metallicity distributions for complete stellar samples in the solar neighborhood. We identify quasi-mono-age-metallicity stellar populations with an age resolution better than $5 \%$ ($\sim 0.5$ Gyr at old age), and study their absolute vertical density profile. We observe a clear correlation between scale height and stellar age, with younger populations consistently more confined to the plane. We find evidence that the scale height decrease rate changed drastically $10.85^{+0.13}_{-0.12}$ Gyr ago: at older ages, the evolution is very steep, with $h_Z$ dropping from over $1.26$ kpc to $\sim 0.5$ kpc in merely $2$ Gyr; subsequently, the thinning is very gradual, with $h_Z \sim 0.1$ kpc for the youngest populations. The extremely rapid early vertical settling of the disk points to a fundamentally upside-down formation process at early times, when the thick disk component is basically formed. We thus strongly support an evolutionary scenario defined by two distinct temporal phases: an initial, highly turbulent epoch that gave birth to the thick disk, and a subsequent more quiescent period of secular evolution and gradual gas settling which formed the thin disk.
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All authors David Mirabal, Carme Gallart, Tomás Ruiz-Lara, Emma Fernández-Alvar, Anna B. A. Queiroz, Guillem Aznar-Menargues, Chris B. A. Brook, Santi Cassisi, Yllari K. González-Koda, Julio F. Navarro, Pedro A. Palicio, Francisco Surot

Astrophysics of Galaxies

No Convincing Evidence for Tidal Binary Clusters in the Galaxy

Juan Casado and Zahra Al

Context. The existence of tidal binary clusters (TBCs) in the Milky Way has been repeatedly suggested using Gaia DR3 astrometry and recent catalogs of binary clusters and groups. However, the dynamical feasibility of forming truly bound binary clusters through tidal capture remains uncertain. Aims. We perform a systematic reassessment of twenty star clusters, currently claimed as members of TBCs from the catalog of binary and grouped clusters of Liu et al. (2025) to ascertain their classification. Methods. For each candidate pair, we use Gaia DR3 astrometry and photometry to perform a simultaneous and self-consistent opti mization of age, distance modulus, reddening, and metallicity. Results. Our analysis shows that all studied TBCs fail in the required physical condition that ages are compatible with independent formation. After applying strict evolutionary criteria, these systems are more naturally explained as co-eval members of primordial cluster pairs or groups rather than products of tidal capture. Conclusions. We conclude that genuine tidal binary clusters, if present in the Milky Way, must be extremely rare. This work un derscores the importance of robust age determinations and physically motivated selection criteria in future searches for dynamically assembled cluster pairs.
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Astrophysics of Galaxies · Cross-listed from astro-ph.SR

The 200-300 GHz Survey for 18 Class II Disks in the Ophiuchus Star-Forming Complex

Chia-Ying Chung, Hauyu Baobab Liu, Chuan-Yung Lin et al. (+4 more)

We measured the 198-310 GHz flux densities of 18 Class II protoplanetary disks in the Ophiuchus star-forming complex using the Submillimeter Array (SMA). The $\sim$200-300 GHz spectral indices ($\alpha_{200-300}$) of these disks are $2.3^{+0.2}_{-0.5}$. In this observed frequency range, emission properties of the Ophiuchus disks are very similar to the 48 spatially compact Class II disks in the Taurus-Auriga region observed in a previous SMA survey. Combining the Ophiuchus and Taurus-Auriga samples, the Pearson correlation coefficient between $\alpha_{200-300}$ and the flux density at 250 GHz ($F_{250\,\mathrm{GHz}}$) is 0.27 ($p=0.02$). We do not find a convincing correlation between $\alpha_{200-300}$ and the $R_{95\%}$ radius of the disks. Our interpretation for the $\alpha_{200-300}$ values being close to 2 in the spatially compact disks is that at $\gtrsim 200$ GHz frequencies, the continuum emission in these disks is dominated by optically thick dust thermal emission, independent of $F_{250\,\mathrm{GHz}}$ and $R_{95\%}$. As a result, the (sub)millimeter luminosity and the apparent disk size are positively correlated, which has been found in numerous resolved emission surveys of Class II disks. In young clusters with ages of $\sim$1-2 Myr, Class II disks with smaller radii or lower (sub)millimeter luminosities are not necessarily those in which the dust mass budget has been consumed or dispersed.
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All authors Chia-Ying Chung, Hauyu Baobab Liu, Chuan-Yung Lin, Linjing Feng, Sean M. Andrews, Mark A. Gurwell, Melvyn Wright

Thursday 1 October

Astrophysics of Galaxies

Star Cluster Populations in 38 Spiral Galaxies: Evidence for Near-Universal Mass and Age Distributions from PHANGS

Rupali Chandar, Matthew R. Floyd, David A. Thilker et al. (+23 more)

We present the largest study to date of star cluster mass and age distributions in nearby galaxies. The analysis is based on a uniformly selected catalog of over 15,000 (36,000) human (machine) classified compact clusters across 38 spiral galaxies in the PHANGS-HST survey, with improved photometric SED age dating that mitigates key degeneracies with reddening and metallicity. The galaxies span a factor of ~100 in star formation rate (SFR) and in their surface density of star formation and molecular gas (Sigma_SFR, Sigma_H2), and cover a broad range of morphologies. We find that cluster mass functions are well described by a power law, dN/dM ~ M^beta, with beta=-1.9 +/- 0.2, and that this shape is remarkably similar across all galaxies in our sample and eight composite groups of galaxies with similar SFRs, with no significant dependence on SFR, Sigma_SFR}, or Sigma_H2. Cluster age distributions decline steeply and can be described by dN/dt ~ t^gamma with gamma=-0.83 +/- 0.24, again with little dependence on host-galaxy properties or cluster mass. The independence of the mass and age distributions implies a separable joint distribution, g(M,t) ~ M^beta t^gamma, and suggests that cluster populations in spiral disks are dominated by strong, mass-independent dissolution over their first ~Gyr. These results establish a benchmark for interpreting cluster demographics across diverse galactic environments and provide context for studies of young cluster populations at high redshift.
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All authors Rupali Chandar, Matthew R. Floyd, David A. Thilker, Kiana Henny, Bradley C. Whitmore, Janice C. Lee, Sinan Deger, Daniel A. Dale, Kirsten L. Larson, Mederic Bouquien, Oleg Gredin, Daniel Maschmann, Adam K. Leroy, Erk Rosolowsky, Leonardo Ubeda, Ashley T. Barnes, Eva Schinnerer, Eric Emsellem, Angus Mok, Kathryn Grasha, Francesca Pinna, Aida Wofford, Ralf S. Klessen, Simon Glover, Sumit K. Sarbadhicary, Ivan Gerasimov

Astrophysics of Galaxies

The Largest Catalog of Dwarf Galaxy Groups: Transient Structures or Building Blocks of the Universe?

Marko Mićić

Elusive dwarf galaxy groups provide a rare opportunity to study hierarchical galaxy assembly at the lowest-mass scales, but whether such associations are gravitationally bound systems or transient configurations remains uncertain. We present the largest catalog of isolated dwarf galaxy groups, identified using the DESI Survey, comprising 74 systems with three to six members per group. The groups have a median line-of-sight velocity dispersion of $\sim53$ km s$^{-1}$ and a median crossing time of $\sim0.37$ Gyr. We find that stellar mass alone is generally insufficient to bind the observed configurations. On the other hand, when dark matter is included using independently inferred stellar-to-halo mass relations and NFW potentials, 69 of 74 systems ($93\%$) favor a bound interpretation after propagating observational and halo-model uncertainties. For the 69 bound-favored systems, dynamical-friction estimates indicate that substantial orbital decay within a Hubble time is plausible if their members retain significant dark-matter subhalos. Our results suggest that many of these groups are systems caught during the assembly of more massive descendants, representing some of the lowest-mass sites of ongoing hierarchical galaxy growth in the nearby Universe and accessible laboratories for a mode of assembly expected to have been prevalent at early cosmic epochs.
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Astrophysics of Galaxies

DESI Interacting Dwarfs Survey: Multiple Evolutionary Channels of Dwarf Galaxies Driven by Major Dwarf Interactions

Marko Mićić and Sugata Kaviraj

Dwarf-dwarf interactions are a major driver of galaxy evolution in the early Universe, but observational constraints on their impact across mass, separation, and environment remain scarce. Using the Dark Energy Spectroscopic Instrument Early Data Release, this study constructs the largest sample of dwarf galaxy pairs, spanning stellar masses $6.5 \leq \log(M_\star/M_\odot) \leq 9.5$ and redshifts $0.015 \leq z \leq 1.5$. We analyze the evolution of star formation rates and multiwavelength colors ($NUV-r$, $U$-$V$, $V$-$J$, $r$-$K$, and $g$-$r$) as a function of projected separation, stellar mass, and external tidal environment. Low-mass/low-redshift pairs exhibit interaction-triggered star formation at intermediate separations. At the smallest separations ($\lesssim$10 kpc), these systems display divergent behavior: isolated pairs show the onset of dust-obscured star formation, those embedded in weak external tidal fields undergo extended, dust-unobscured star formation, while those embedded in strong external tidal fields experience rapid quenching of star formation. High-mass/low-redshift pairs follow a more uniform evolutionary track, with generally weaker dependence on environment. Interaction-triggered star formation occurs at intermediate separations, followed by increased dust obscuration and rapid quenching at the smallest separations. At higher redshifts, high-mass dwarf systems display an initial suppression of star formation, followed by renewed activity at smaller separations, consistent with early-stage gas removal and later interaction-driven inflows. These results demonstrate that dwarf-dwarf interactions do not follow a single evolutionary pathway. Instead, we reveal a complex picture of dwarf galaxy evolution, with significant implications for dust-obscured star formation, abrupt quenching, and the formation of compact, dusty, intensely star-forming systems.
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Astrophysics of Galaxies

Super-resolving Polarized Dust Emission with Transformer-Based Multi-Tracer Fusion

Minjie Lei, George Halal, S. E. Clark et al. (+3 more)

Realistic models of polarized Galactic dust emission at high angular resolution are essential for component separation in next-generation cosmic microwave background (CMB) $B$-mode experiments. However, existing dust polarization templates are constrained only to ~1 degrees, and it remains challenging to develop models that can generate realistic small-scale complexity that is also coherently connected to the well-measured large-scale structures. In this work, we develop a data-driven super-resolution framework that predicts small-scale dust polarization structure directly from multiple tracers observed at high resolution. We combine the Planck dust optical depth $\tau_{353}$, \ion{H}{1}-based Stokes templates, and coarse Planck GNILC $Q$ and $U$ maps in a transformer-based model trained to recover native-resolution GNILC polarization from a $4\times$ beam-smoothed version of itself, so that the network solves a deconvolution problem informed by the structure of multiple tracers rather than generating structure to match a target statistic. Applying the model to the uniform-resolution GNILC maps, we produce $Q$ and $U$ predictions at 20' over the high-latitude (|b|>30 degrees) sky. Using scalar and tensorial Minkowski functionals and scattering transform statistics, we find that our maps exhibit more coherent, anisotropic, and filamentary small-scale structure than the latest PySM dust model. Our results establish data-driven learned deconvolution as a promising route to foreground models whose small scales are inferred from data rather than prescribed.
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All authors Minjie Lei, George Halal, S. E. Clark, Alejandro Dobles, Katie Brown, Viraj Manwadkar

Astrophysics of Galaxies

X-ray Characterization of Galaxy Groups and Hickson Groups in COSMOS-Web to z~3.8 I. X-ray Luminosity Function Evolution

Ghassem Gozaliasl, Günther Hasinger, Gavin Leroy et al. (+35 more)

Galaxy groups are the dominant halo environment in the Universe and a sensitive laboratory for feedback and gas-cycling physics, yet a uniform, intermediate-redshift X-ray characterization of the group population has been limited by the availability of deep, wide-area imaging. We present a uniform X-ray characterization of the COSMOS-Web galaxy group population: 1,678 groups (CW-All) identified with the AMICO algorithm applied to the JWST-selected COSMOS-Web photometric catalog ($0.08 \lesssim z \lesssim 3.7$), and a parallel sample of 993 Hickson compact groups (CW-HCG; $0.08 \lesssim z \lesssim 3.82$) over $0.45~\mathrm{deg}^2$. We apply a uniform aperture-photometry X-ray pipeline to the combined Chandra and XMM-Newton COSMOS mosaic, measuring fluxes, luminosities, temperatures, and halo masses and radii for every group, together with detections, upper limits, and quality flags. We detect X-ray emission from 499 CW-All groups (29.7%) and 332 CW-HCG groups (33.4%) at SNR~$\geq 2.0$, and present the X-ray luminosity function in four redshift bins. The characteristic luminosity $L^\star$ rises monotonically by $\sim$1.9–2.1~dex from the lowest to highest redshift bin in both catalogs, a trend that persists under two independent cross-check binning schemes and is not explained by mass or richness selection of the detected population. A targeted search for diffuse X-ray emission from the AmicOne protocluster candidate at $2.50 \lesssim z < 3.09$ finds no statistically significant signal at the current depth. We publicly release the X-ray measurements and derived properties for both catalogs.
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All authors Ghassem Gozaliasl, Günther Hasinger, Gavin Leroy, Alexis Finoguenov, Fatemeh Abedini, Hollis B. Akins, Rafael C. Arango-Toro, Arif Babul, Caitlin M. Casey, Nicole E. Drakos, Andreas L. Faisst, Carter Flayhart, Maximilien Franco, Zohreh Ghaffari, Santosh Harish, Hossein Hatamnia, Olivier Ilbert, Jeyhan S. Kartaltepe, Ali Ahmad Khostovan, Maarit Korpi-Lagg, Ronaldo Laishram, Daizhong Liu, Matteo Maturi, Henry Joy McCracken, Jed McKinney, Nicolas McMahon, Lauro Moscardini, Mahdiyar Mousavi-Sadr, Jason Rhodes, Brant E. Robertson, Louise Paquereau, Rasha M. Samir, Mark Sargent, Diana Scognamiglio, Marko Shuntov, Greta Toni, Francesco Ubertosi, Eleni Vardoulaki

Astrophysics of Galaxies

Separating the Optical to Near-Infrared Light of AGN and Their Host Galaxies

Callum Dewsnap, Pauline Barmby and Sarah C. Gallagher

The properties of galaxies that host active galactic nuclei (AGNs) offer clues to the conditions that enable accretion onto supermassive black holes. A galaxy's morphology can provide significant information on the evolutionary processes underway. By modeling the surface-brightness profiles of galaxies that host AGN, we can characterize physical properties of the host galaxy. With a sample of sources across a wide range of redshifts, we can investigate how both the supermassive black hole and galaxy evolve over time. Applying the best practices from previous work, we perform Sersic + point source fits of 96 X-ray-selected AGN in the Extended Groth Strip across up to 13 bands of James Webb Space Telescope and Hubble Space Telescope imaging using AstroPhot. We examine both parametric (Sersic) and nonparametric methods in tandem to best determine the physical properties of the host galaxy. After separating the light of the host galaxy and the AGN, we perform independent CIGALE model fits to photometric spectral energy distributions to estimate physical properties including the host galaxy stellar mass and star formation rate, and AGN disk luminosity. In the stellar-mass/star-formation-rate plane, the AGN host galaxies align with the population of massive non-AGN galaxies in the control sample across all redshifts. The AGN disk luminosities result in ratios of bolometric to X-ray flux within the expected range, 5-20:1. We provide an evaluation of the limitations of Sersic modeling to obtain galaxy properties and provide recommendations on best practices for multi-band AGN+host galaxy image decomposition with James Webb Space Telescope imaging.
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Astrophysics of Galaxies

Collapse-accelerated small-scale dynamos in the first stars and galaxies

Muhammed Irshad and Pallavi Bhat

Here, we explore magnetic field amplification by the small-scale dynamo (SSD) during the formation of the first stars and galaxies. Gravitational collapse continuously modifies turbulent velocities and length scales, making the SSD fundamentally different from a dynamo operating in stationary turbulence. In arXiv:2503.19131, we developed a supercomoving formulation of turbulent dynamos and showed that the increasing dynamo growth rate during collapse leads to super-exponential (SE) magnetic field amplification in the kinematic stage. Here, we show that collapse also accelerates the slower nonlinear stage, allowing magnetic energy to reach progressively larger scales. We apply this framework to first-star and first-galaxy formation and find that the impact of collapse depends strongly on the dynamo efficiency. If the dynamo is sufficiently fast, the field reaches saturation before substantial collapse occurs, leaving little room for further acceleration. At the opposite extreme, if the dynamo is too slow, dynamo amplification remains weak and flux freezing dominates. Between these limits, collapse can substantially accelerate the dynamo, with speed-ups of >10 in the parameter space explored, enabling dynamically significant fields to develop within the available collapse time. Nonlinear scale-by-scale saturation further produces fields correlated on a non-negligible fraction of the system. We provide estimates and scaling relations for the final field strength and correlation scale and their dependence on halo, turbulence, dynamo, and collapse parameters. The earlier emergence of dynamically important fields can affect fragmentation, angular-momentum transport, and the subsequent evolution of the first stars and galaxies.
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Astrophysics of Galaxies · Cross-listed from astro-ph.HE

Neutrino flavor instabilities intermediate between slow and fast

Nicolas Viaux and Lucas Johns

The neutrino flavor composition in supernovae and neutron star mergers is shaped by flavor instabilities, which are commonly classified into three types: slow (SFI), fast (FFI), and collisional (CFI). The focus here is on mixed-type instabilities combining attributes of the standard varieties. We examine instability growth rates in two-dimensional parameter spaces (“phase diagrams”) whose axes correspond to instabilities of pure type. We find critical curves connecting the pure-type instability onset points. We also exhibit qualitative trends in the growth-rate spectra $\gamma_{\bm{k}}$, emphasizing the occurrence of crossovers and phase transitions in the fastest-growing Fourier mode $k_{\textrm{max}}$ and drawing attention to the distinction between spatial-mean ($\bm{k} = 0$) and flavor-wave ($\bm{k} \neq 0$) instabilities. Our paper is a step toward understanding flavor instabilities as they actually occur in nature rather than in idealized limits.
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Astrophysics of Galaxies

Inferring magnetic field strengths in high-redshift lensing galaxies from Faraday rotation measure observations

Stefan Reissl, Ralf S. Klessen, Annalisa Pillepich et al. (+3 more)

Observations of Faraday rotation in the lensing galaxy of CLASS B1152+199 at z = 0.439 suggest that efficient dynamo mechanisms had already amplified galactic magnetic fields by this epoch. We assess the reliability of this method for deriving magnetic field strengths and the likelihood of observing similarly large Faraday rotation differences. We select 64 star-forming disk galaxies from the TNG50 cosmological magnetohydrodynamical simulation, matched to CLASS B1152+199 in mass and redshift, and forward model them using polarized radiative transfer with POLARIS and subsequent RM synthesis. TNG50 predicts characteristic large-scale field strengths of B$_0$ = 1.9-15.6 $\mu$G for individual galaxies, while the combined sample yields B$_0$ = 10.3 $\mu$G. Field strengths B$_{obs}$ inferred from the synthetic observations generally recover B$_0$ within a factor of three. B$_{obs}$ depends only weakly on the assumed magnetic field geometry, whereas galaxy inclination and beam depolarization have stronger effects. The differential rotation measure recovered from RM synthesis remains correlated with the directly integrated value, although beam depolarization systematically reduces its magnitude. Only 1.41% of directly integrated sightline pairs reproduce the observed $\Delta$RM = 1040 $\pm$ 60 rad m$^{-2}$ of CLASS B1152+199, increasing to 3.16% for sightlines at galactocentric distances comparable to the observed 2.6 and 6.5 kpc. Differential Faraday rotation of gravitationally lensed sources therefore provides a robust probe of large-scale magnetic fields, while the large $\Delta$RM of CLASS B1152+199 is relatively rare among the considered TNG50 analog galaxies.
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All authors Stefan Reissl, Ralf S. Klessen, Annalisa Pillepich, Sui Ann Mao, Rüdiger Pakmor, Dylan Nelson

Astrophysics of Galaxies

Towards robust simulations of the galactic dynamo: a cross-code comparison between Eulerian and Lagrangian schemes

Mark Ivan Ugalino, Benedikt Diemer, Vadim A. Semenov et al. (+8 more)

Galactic magnetic fields are thought to be seeded by microscopic processes such as the Biermann battery and are primarily amplified to observed microgauss strengths by dynamo processes. Much of this amplification likely occurs within proto-galaxies, where turbulent and rotational kinetic energy is converted into magnetic energy via dynamo action. However, two aspects of this process remain poorly constrained in simulations: the saturation level of the amplified field and the timescale on which it is reached. In particular, different numerical methods, resolution strategies, and subgrid prescriptions have not converged to similar results, making it difficult to establish robust, code-independent conclusions about dynamo amplification in galaxies. In this work, we present the first systematic comparison of both Eulerian and Lagrangian codes that employ diverse MHD schemes, including ART, RAMSES, AREPO, and SWIFT. Using identical initial conditions for Milky Way-type galaxies and without including star formation and stellar feedback, we find that the amplification history of the magnetic field within the galactic disk depends strongly on the choice of hydrodynamical scheme, with orders-of-magnitude differences between Eulerian and Lagrangian approaches. We further demonstrate that reducing the mesh velocity in the moving-mesh code AREPO leads to results consistent with those obtained using the static grid codes ART and RAMSES. These results highlight the importance of carefully assessing numerical effects when interpreting magnetic field amplification in galaxy simulations.
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All authors Mark Ivan Ugalino, Benedikt Diemer, Vadim A. Semenov, Jin Young Kim, Federico Marinacci, Christoph Pfrommer, Matthieu Schaller, Nikyta Shchutskyi, Volker Springel, Romain Teyssier, Oliver Zier

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

The Impact of a Clumpy Ambient Medium on the Dynamics and Synchrotron Emission of AGN Jets

Ivan Almeida, Christian Fendt and Bhargav Vaidya

Relativistic jets from AGN are expected to propagate through an inhomogeneous ISM, but the role of small-scale gas inhomogeneities in shaping their early evolution remains uncertain. We investigate this problem using 3D special-relativistic magnetohydrodynamic simulations with PLUTO, following a jet with a Lorentz factor of 10 propagating through a pc-scale medium. We compare a homogeneous ambient medium with two clumpy ambient-medium models, motivated by dense gas in the nuclear ISM, in which clouds occupy volume filling factors of $0.1$ and $1$ per cent. We compute synthetic synchrotron maps and spectra from Lagrangian macro-particles that have been accelerated by diffusive shock acceleration. Jet-cloud interactions deflect the flow, enhance shock formation, and produce a more asymmetric cocoon than in the homogeneous ISM case. Altogether, this results in a substantially stronger mass loading: the entrained mass increases from $0.43$ M$_{\odot}$ in the homogeneous run to $5.3$ and $8.8$ M$_{\odot}$ in the clumpy runs. The clumpy ISM also modifies the turbulence and the material mixing within the jet cocoon. The dynamical differences we find translate into brighter and more irregular synchrotron emission. For the same injected jet, the models with a clumpy medium produce stronger frequency-integrated synchrotron emission than the homogeneous run, with the largest differences in the SED occurring from the sub-mm to the infrared/optical bands. Our results demonstrate that including a small-scale ISM structure provides a more complete description of the early dynamical evolution of young AGN jets and their radiative properties.
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Astrophysics of Galaxies

Diverse Protoclusters at $z\sim3$ Disclosed by Systematic Spectroscopy

Jun Toshikawa, Kentaro Koretomo, Nobunari Kashikawa et al. (+6 more)

We present the results from follow-up spectroscopy of three protocluster candidates at $z\sim3$, selected as overdense regions of $U$-dropout galaxies in the wide-field imaging of the Hyper SuprimeCam Subaru Strategic Programme. All three targets exhibit tight clustering in three-dimensional space, i.e. on the sky ($>4\sigma$ overdensity) and in redshift ($>98.4\%$ confidence), making for clear evidence of genuine protoclusters. Since these three protoclusters are identified by the same dataset and technique, they represent a good sample to study the diversity of protocluster properties with minimal observational biases. Although the average population across the three protoclusters is consistent with field galaxies, each protocluster individually exhibits distinguishing properties from each other or from field galaxies. In one protocluster, member galaxies stand out by a higher Ly$\alpha$ equivalent width ($EW_0$), and massive members that are still highly star-forming. In contrast, relatively more suppressed star formation appears in another protocluster where the Ly$\alpha$ $EW_0$ of member galaxies is systematically lower. These variations can be attributed to differences in the developmental phase of protoclusters. If the presence of quenching galaxies indicates a more mature system, galaxies with stronger Ly$\alpha$ emissions may be more prevalent in the earlier stages of cluster formation. The uniform approach to searching protoclusters on which this study builds enables us to link observed variations at the onset of cosmic noon to different pathways in the history of cluster formation.
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All authors Jun Toshikawa, Kentaro Koretomo, Nobunari Kashikawa, Stijn Wuyts, Marcin Sawicki, Malcolm N. Bremer, Yoshiaki Ono, Mariko Kubo, Tomoki Saito

Astrophysics of Galaxies

Galaxy Protoclusters as Drivers of Cosmic Reionization: II. Te-Based Metallicities of Lyman-{\alpha} Emitters

C. Moya-Sierralta, C. L. Martin, L. F. Barrientos et al. (+15 more)

Context. Protoclusters at reionization are thought to host a significant fraction of the cosmic star formation rate density, making them crucial for the timing and topology of reionization. The gas-phase metallicity, a key tracer of galaxy evolutionary stage, can now be measured directly in the early Universe with JWST. Aims. We measure the gas-phase metallicity of Lyman-$\alpha$ emitters (LAEs) in the LAGER-z7OD1 protocluster at $z\approx6.93$ via the direct ($T_e$-based) method using the [O III]$\lambda$4363 auroral line, and combine it with stellar masses to constrain the mass-metallicity relation (MZR) in dense environments. Methods. We use JWST/NIRSpec MSA G395H spectroscopy, derive metallicities with self-consistent analytic prescriptions, and propagate the dust-extinction uncertainty into an asymmetric error budget via Monte Carlo simulations based on the observed Balmer decrements. Stellar masses come from BEAGLE SED fitting of JWST/NIRCam and UltraVISTA photometry. Results. We obtain five secure [O III]$\lambda$4363 detections and one upper limit, with 12+log(O/H) $\approx$ 7.2-8.0. The weighted spectral stack yields 12+log(O/H) = $7.76^{+0.06}_{-0.05}$, ~0.26 dex higher than stacks of LAEs at similar redshifts from JWST surveys. However, the MZR fit gives a slope $\gamma$ = 0.232 +/- 0.214 and normalization $Z_0$ = 7.888 +/- 0.199, placing our sources below the established MZR of normal galaxies and recent protocluster baselines at $z\sim5-7$. Conclusions. The higher metallicity relative to general LAEs suggests accelerated assembly driven by the overdensity, while the offset below the MZR points to a complex interplay between mass build-up and gas accretion. Since we target actively star-forming LAEs, we are likely capturing a phase of pristine gas inflow from the intergalactic medium that fuels star formation but dilutes the interstellar media of these protocluster members.
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All authors C. Moya-Sierralta, C. L. Martin, L. F. Barrientos, L. Infante, J. González-López, W. Hu, A. L. Faisst, Y. Harikane, A. M. Koekemoer, S. Malhotra, M. Ouchi, Z. Peng, J. Rhoads, J. Wang, J. R. Weaver, I. Wold, J. Yang, Z. Zheng

Astrophysics of Galaxies

Weighing Galaxies Inside-Out: Small-Scale Lensing and the Stellar Mass Problem

Divya Rana, Henk Hoekstra, Konrad Kuijken et al. (+2 more)

Small-scale galaxy-galaxy weak lensing provides an independent way to probe the stellar initial mass function by constraining the matter distribution within galaxies. We forecast the potential of upcoming Euclid observations using realistic mock catalogues designed for a DESI-like Bright Galaxy Survey, which is expected to cover approximately $9000\,\mathrm{deg}^2$ of the Euclid wide survey area. We assess the impact of foreground lens light, which introduces significant scale-dependent biases in source detection, photometry, and shape measurements. Subtracting the lens light with Galfit reduces these biases by nearly an order of magnitude at scales down to four times the half-light radius. We model the predicted lensing signal around central galaxies with stellar masses between $9.5 \leq \log(M_*/h^{-2}M_\odot) \leq 11.5$ over projected separations of $10$ to $100\,h^{-1}\mathrm{kpc}$. The resulting signal-to-noise ratios reach $\sim 150$ for intermediate-mass galaxies. Assuming an NFW profile for the dark matter contribution, we constrain the stellar mismatch parameter $\alpha$ to a precision of approximately $8.5$ percent for the full sample and $8.6$ percent for massive galaxies. These results highlight the potential of small-scale galaxy–galaxy weak lensing as a robust probe of the IMF and the connection between stellar and dark matter in galaxies using upcoming Euclid data.
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All authors Divya Rana, Henk Hoekstra, Konrad Kuijken, Alessandro Sonnenfeld, Maryam Tajalli

Astrophysics of Galaxies

Constraining the density distribution of the cold Circumgalactic Medium of quasars at z>2 through Lya, HeII and Ha emission

Andrea Travascio, Sebastiano Cantalupo, Titouan Lazeyras et al. (+16 more)

Extended Lya emission is routinely detected around high-redshift quasars, revealing large reservoirs of cool circumgalactic medium (CGM). Its resonant nature complicates interpretation of gas density, ionization state, and kinematics, making non-resonant tracers such as HeII and Ha essential. Extending previous analytical models, we use CLOUDY photo-ionization simulations to predict HeII/Ha in quasar-illuminated gas over a broad parameter range, including log-normal density distributions. The ratio constrains density fluctuations, commonly quantified by the clumping factor C. We compare the models with extended Lya, HeII, and Ha observations around quasars at z~2.1-4.5. At z~2.2, we observed 13 quasars with Keck/KCWI and targeted the systems with the most prominent extended Lya and HeII emission with Keck/MOSFIRE, providing the first statistical quasar-CGM sample with combined Lya, HeII, and Ha measurements. Within matched apertures out to ~35 pkpc, stacked spectra give Lya/Ha=9.1, HeII/Ha=0.54, and HeII/Lya=0.06. Single-density models require very high CGM densities (n>10 cm^-3) or implausibly soft AGN spectra to reproduce the low HeII/Ha ratio. Broad log-normal density distributions instead reproduce it at lower median densities but require a substantial emissivity-weighted high-density tail, corresponding formally to C~10^3-10^4 in our parameterization. We also analyze 26 VLT/MUSE quasars at 3.1<z<4.5, where Ha is inaccessible from the ground, finding 14 systems with co-spatial extended Lya and HeII emission. The detected, emission-weighted HeII/Lya component shows no evidence for strong evolution between z~2.2 and z~3.7, though this does not imply an invariant underlying density PDF. These constraints provide a basis for comparison with theoretical models and hydrodynamical simulations of the physical processes shaping quasar CGM at high redshift.
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All authors Andrea Travascio, Sebastiano Cantalupo, Titouan Lazeyras, Naveen A. Reddy, Charles C. Steidel, Yongming Liang, Gabriele Pezzulli, Massimo Gaspari, Matteo Fossati, Michele Fumagalli, Chiara Feruglio, Fabrizio Fiore, Huiyang Mao, Marta Galbiati, Weichen Wang, Nicolas Ledos, Bahram Mobasher, Antonio Pensabene, Giada Quadri

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

Detection of kilosecond hard lags in the new pulsating ULX candidate NGC 7456 ULX-1

W. Leone, F. Pintore, C. Pinto et al. (+19 more)

Context. Ultraluminous X-ray sources (ULXs) are thought to be powered, in many cases, by super-Eddington accretion onto compact objects. While soft X-ray lags have been detected in several ULXs, hard lags remain rare and poorly understood. Aims. We investigate the temporal and energy dependence of X-ray lags in NGC 7456 ULX-1 to constrain their physical origin and probe the super-Eddington accretion flow. Methods. We analyzed the two deepest XMM-Newton observations, taken in 2018 and 2023. Hard (1-10 keV) and soft (0.3-1 keV) light curves were cross-correlated using adaptive-binning techniques optimized for Poissonian low-count data. We measured lags over consecutive 10 ks intervals and investigated their energy dependence. Spectra were modeled using thermal and Comptonization models. Results. We detect significant hard X-ray lags in both observations, with the hard emission delayed by $\sim 10^3$ s during phases of rapid flux variability. The delays are primarily driven by the lowest-energy photons. Spectral modeling indicates a Comptonization-dominated flow comprising a cooler, extended outer region and a hotter, compact inner flow embedded in an optically thick wind. We interpret the delays as the combined effect of inward propagation of accretion-rate fluctuations and photon diffusion within the dense outflow. Fluctuations first enhance the soft-emitting outer regions and then propagate toward the hotter inner flow, where photons undergo stronger Comptonization before escaping with a kilosecond delay. The small inferred inner emitting radius disfavors an intermediate-mass black hole accretor. Conclusions. The sign, amplitude, and energy dependence of the delays disfavor standard reverberation. Propagation-driven variability coupled with radiative transfer in optically thick winds appears to play a major role in shaping the timing properties of super-Eddington accretion flows.
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All authors W. Leone, F. Pintore, C. Pinto, N. O. Pinciroli Vago, A. Sanna, A. Wolter, T. Di Salvo, R. Iaria, A. D'Aì, A. Anitra, R. Soria, P. Esposito, F. Barra, E. Ambrosi, S. Caserta, C. Salvaggio, R. Salvaterra, G. L. Israel, S. Banerjee, M. Marelli, G. Rodriguez-Castillo, L. Burderi