arXane › Physics › Astrophysics
Wednesday, 4 November 2026: 29 new papers, 4 cross-lists and 15 replacements in Astrophysics of Galaxies (astro-ph.GA), in arXiv's order, with full abstracts. The same papers as arXiv's own listing, set as a newspaper; every title links to arXiv.
JWST has revealed an unexpected abundance of z>10 galaxies and striking spectral diversity. Here, we model bursty star formation histories (SFHs) to explore how they shape this diversity and whether spectroscopy can discriminate between explanations for the UV luminosity function (UVLF) excess. We find strong burstiness ($\sigma_{UV}(M_h=10^{10}M_\odot)$~0.9 mag), increasing toward low halo masses, is required to reproduce the z~6 UVLF and observed fractions of galaxies in recent star formation upturns and downturns, traced by SFR$_3$/SFR$_{50}$. This burstiness naturally reproduces UVLFs and SFR upturn and downturn fractions over z~6-11. With increasing redshift, we predict galaxies in recent upturns (SFR$_3$/SFR$_{50}>5$) increasingly dominate the UVLF bright end, reflecting rising accretion rates and burstier low-mass halos. This results in higher median emission-line equivalent widths (EWs), bluer UV slopes and weaker Balmer breaks at fixed $M_{UV}$, while distributions of these properties broaden. We find the downturn fraction (SFR$_3$/SFR$_{50}<0.2$) is particularly sensitive to stochasticity: increasing towards faint $M_{UV}$ if burstiness increases in lower mass halos, and evolving with redshift only if stochasticity does. However, the model underpredicts the z~14 UVLF, so we explore two models which match the UVLF: increased burstiness and increased star formation efficiency. From z=10 to 14, at fixed $M_{UV}$, increased burstiness predicts the downturn fraction increases by ~2x and the weak-emitter fraction (H$\beta$ EW<50{\AA}) by ~1.5x. By contrast, the increased efficiency model predicts a constant downturn fraction and declining weak-emitter fraction. Overall, our results indicate burstiness is important for explaining spectral diversity and evolution at z~6-14, and that spectroscopic samples spanning a broad $M_{UV}$ range can establish its role in the z~14 UVLF excess.
The Gaia mission has greatly improved our understanding of the stellar binary population. Beyond providing an extensive catalog of binary systems with two luminous stars, Gaia has also discovered several systems that appear to be star--black hole (BH) binaries. One of the leading candidate formation channels for these systems is dynamical exchange, in which one component of a star--star binary is ejected from the system and replaced by a BH. Exchange processes are very sensitive to the velocity distribution of the incoming objects, and become very efficient in the limit that perturbers are slow, so the exchanged binary population is a sensitive probe of slow-moving objects. A population of slow-moving, nonluminous objects is naturally produced in dissipative dark matter (DDM) scenarios, where a subcomponent of dark matter can cool to form a dark disk and dark compact objects (DCOs), including but not limited to BHs, with a small velocity dispersion. In this work, we evaluate the rate at which DCOs formed by DDM exchange into star--star binaries to form star--DCO binaries. We find that in a wide range of parameter space, even under conservative assumptions, the rate of exchange interactions is sufficient to produce the objects that Gaia has observed to date. In some portions of parameter space, the predicted exchange rate is well in excess of the rate estimated from observations. We point out the potential for competitive constraints on the DDM parameter space with current and future data, making the Gaia mission an important testbed for dark sector cooling.
The origin of anomalous chemical enrichment in high-redshift galaxies discovered by JWST remains a key question in galaxy evolution. Enhanced nitrogen abundances have been identified in several galaxies at early cosmic times, but the physical conditions driving this enrichment, and their connection to galaxy morphology, remain unclear. We test whether morphologically compact galaxies at 4 < z < 7 show stronger chemical anomalies than extended systems. Using JWST/NIRSpec spectroscopic data, we construct samples of compact and extended galaxies and analyse their rest-frame spectra. We stack the spectra of each population and measure key UV and optical emission lines. We detect nitrogen emission in the compact galaxy stack, including NIV], and [NII], while also detecting key carbon and oxygen lines. The detection of [OIII]{\lambda}4363 enables a direct-Te determination of the oxygen abundance. From these measurements, we infer chemical abundance ratios, including log(N/O) and log(C/O). We find that compact galaxies exhibit elevated log(N/O) (by ~ 0.7 dex) and log(C/O) (by ~ 0.5 dex) abundance ratios relative to extended systems. The abundance patterns of compact galaxy stacks are comparable to those of previously identified individual nitrogen-enhanced galaxies at high redshift and second-generation globular-cluster stars in the Milky Way. These results suggest a possible link between galaxy compactness and chemical enrichment pathways in the early Universe. Deeper JWST NIRSpec IFU observations of compact high-redshift galaxies will be crucial for determining the origin, spatial distribution, and evolutionary significance of these abundance patterns.
JWST has found many faint broad-line AGN at $z>4$, but it is unclear whether the Ly$\alpha$ we see from them comes from the accreting black hole or from its host galaxy. The answer matters for how these sources are interpreted and for how many ionizing photons they release. We use deep JWST/NIRSpec spectroscopy from the DIVER program to measure Ly$\alpha$ in 12 compact broad-line emitters (CBEs) at $z=4.2$--5.5 in GOODS-N. CBEs include little red dots (LRDs), little blue dots, and other broad-line AGN. Six are detected in Ly$\alpha$. Every source shows a broad-line region, yet Ly$\alpha$ does not follow it: the sources with the strongest H$\alpha$ relative to the UV include weak detections and nondetections, and every detected Ly$\alpha$ line (FWHM $\approx300$--1000~km~s$^{-1}$) is narrower than broad H$\alpha$ (1100--3300~km~s$^{-1}$). Instead, Ly$\alpha$ appears to track the host galaxy. We model the AGN-subtracted host with a dust-attenuated SED fit. Including the upper limits, the observed Ly$\alpha$ follows the Ly$\alpha$ production in this host model more closely than it follows H$\alpha$/UV, in both equivalent width and luminosity. Every detection exceeds its host-model value by a factor of 1.5--18, leaving room for a nuclear contribution. The black hole is visible in these sources, but the Ly$\alpha$ we observe is more closely tied to its host. The median effective Ly$\alpha$ escape fraction of the detections is only 0.09, which suggests that ionizing escape from CBEs is typically modest and varies widely.
The recent discoveries of high-redshift quasars at $z\sim6-10.1$ present a challenge to conventional supermassive black hole (SMBH) formation scenarios: their central SMBHs are too large to have grown from early stellar remnants, even under efficient super-Eddington accretion. An alternative approach is the direct collapse of primordial, dust- and metal-free gas clouds into black hole seeds as early as $z\sim20$. To prevent fragmentation from highly efficient molecular hydrogen cooling and allow such a collapse, a strong flux of UV photons is required to photodissociate molecular hydrogen, suppressing star formation. We investigate whether the decay or annihilation of dark matter with masses below $\sim200$ eV can produce sufficient UV radiation, both from the cosmological background and within early dark matter halos. Using thermal simulations of a one-zone primordial gas cloud model with the Grackle chemistry and cooling library, we map the resulting gas behavior across a range of dark matter lifetimes, cross sections, and masses. From this, we determine regions of parameter space where direct collapse into an SMBH is possible and the corresponding maximum halo mass required.
The distinction between brightest cluster galaxies (BCGs) and intracluster light (ICL) remains ambiguous, with inferred cluster properties depending strongly on the adopted definition and measurement methodology. We report the presence of a common inflection feature in the radial profiles of surface brightness, ellipticity, and position angle of BCG+ICL systems, indicative of a structural transition in the underlying stellar distribution. Using a combination of low redshift clusters (z < 0.1) observed with the Wendelstein Wide Field Imager, deep Hyper Suprime-Cam observations of clusters at 0.2 < z < 0.4, and cosmological hydrodynamical simulations from Horizon-AGN and Hydrangea, we consistently identify a common inflection at radii of 60-85 kpc. We interpret this feature as a characteristic transition in the combined BCG+ICL light distribution, that may reflect the hierarchical assembly of the cluster. The persistence of this feature across multiple photometric bands, redshift ranges, and simulations supports its robustness. To identify these transitions, we employ an automated second derivative based approach that does not rely on parametric decompositions or arbitrary surface brightness thresholds. This framework provides a physically motivated and scalable means to characterise the BCG-ICL transition, and it will be of paramount importance for forthcoming large scale surveys such as the Legacy Survey of Space and Time and the European Space Agency's Euclid mission.
Meteoritic inclusions indicate that the early Solar System contained a substantial abundance of the short-lived radionuclide 10Be. Whether it was inherited from the parent molecular cloud or requires local irradiation or late injection remains debated. Here we present the first three-dimensional simulations of a Milky Way-like disc that follow the multi-phase interstellar medium, cosmic rays (CRs), and the production and transport of 10Be by galactic CRs (GCRs) and in supernova remnants (SNRs). Nearly all 10Be is produced by GCR interactions; SNRs contribute at most about ten percent of the 10Be inherited by newly formed stars. The 10Be/9Be ratio traces the CR energy density, declining smoothly with galactocentric radius, and because stars form where supernovae inject CRs, their natal gas is CR-enriched roughly fivefold relative to the mean interstellar medium, which one-zone estimates miss. Accounting for a possibly higher Galactic star formation rate 4.6 Gyr ago, inheritance of GCR-produced 10Be can then explain the early Solar System's 10Be/9Be in our models, without late injection or local irradiation. Even when GCR-induced 10Be production in dense gas is reduced tenfold, the meteoritic value is reached in the innermost disc and missed by only a factor of a few elsewhere, so the main conclusion is robust to uncertain low-energy GCR penetration. The inferred birth radius of the Sun depends strongly on the CR diffusivity, ranging between 3 and 8 kpc, suggesting that improved modelling of low-energy CR transport could sharpen constraints on the birthplace of the Solar System.
Intermediate-mass black holes (IMBHs, $10^2 < m_{\rm BH}/\mathrm{M}_{\odot} < 10^5$) are elusive objects bridging the gap between stellar-mass and supermassive black holes, whose origin remains uncertain. They may form from the collapse of very massive stars (VMSs, $m_*\geq150\,\mathrm{M}_{\odot}$) assembled through repeated stellar collisions in compact and fast evolving star clusters. We investigate the formation of VMSs and IMBH seeds via repeated mergers and collisions as a function of cluster initial conditions, assessing the implications for globular clusters and dense high-redshift system. We develop STARfall, a semi-analytic tool that follows the evolution of a massive stellar binary via binary-single interactions, mergers, collisions, and stellar evolution, while consistently accounting for the host cluster evolution. Our results show that clusters with central densities above $10^6\,\mathrm{M}_{\odot}\,\mathrm{pc}^{-3}$ can undergo a catastrophic sequence of stellar collisions, or "starastrophe", within $3$ Myr. Through this process, VMSs rapidly grow in mass and collapse into IMBHs with masses of up to $10^3-10^4\,\mathrm{M}_{\odot}$, despite the effects of intense stellar winds. Applying our models to observed systems, we find that compact clusters in the Cosmic Gems Arc and Milky Way globular clusters could have hosted VMSs that collapsed into IMBHs in this mass range. Despite their longer core-collapse timescales, the inferred central densities of Little Red Dots may also support IMBH formation in the same mass interval. Our models show that VMS assembly requires two essential ingredients: short core-collapse times and large central densities. Compared to observed systems, our models suggest that clusters in the Cosmic Gems Arcs and several Galactic globular clusters could have nurtured VMSs that directly collapsed to IMBHs with masses $10^3-10^4\,\text{M}_{\odot}$.
The baryon fraction provides a fundamental diagnostic of baryonic matter distribution within dark matter halos and the baryon cycle. While its cosmic value is well constrained, the baryon content within halos on nearly all scales is significantly lower than the cosmic mean; this is called the ``missing baryon problem.'' Using the high spatial, mass, and temporal resolutions of the NewCluster simulation, we investigate the baryon fraction evolution by tracing halo assembly histories from merger trees and gas tracer particles. We identify three distinct evolutionary phases: an early growth phase driven by cold accretion in low-mass halos, a suppression phase likely dominated by supernova feedback, and a recovery phase in massive halos enabled by deeper potential wells and hot-mode accretion. We further find that the redshift dependence of baryon fraction, particularly in low-mass halos, is influenced by the thermal state of the intergalactic medium, with suppression emerging after the surrounding gas becomes persistently hotter than the halo virial temperature. In addition, the scatter in baryon fraction at fixed halo mass correlates with the large-scale environment, with baryon-rich halos preferentially residing closer to filamentary structures. Overall, our results highlight that baryon fraction evolution is governed by the interplay between feedback and environment, requiring a time-resolved perspective on the baryon cycle.
The Seyfert 1 galaxy H 0557$-$385 (z = 0.034) has long been classified as radio-quiet on the basis of its radio-to-optical flux ratio, yet its radio properties are physically inconsistent with this designation. We present a broadband ($0.076 - 258.8$ GHz) radio spectral analysis combining new Australia Telescope Compact Array (ATCA) observations with archival Murchison Widefield Array (MWA), Australian Square Kilometre Array Pathfinder (ASKAP) and Atacama Large Millimeter/submillimeter Array (ALMA) data. The spectrum requires a two-component model: a compact, self-absorbed component with a stratified gigahertz-peaked (GPS)/high-frequency-peaked (HFP) spectral shape (turnover at $9.4^{+0.6}_{-0.5}$ GHz), superposed on an extended, optically thin power-law lobe ($\alpha_{\rm pl} = -0.78$) that dominates below ~1.6 GHz. The derived parameters $-$ a source size of ~15 pc, an equipartition magnetic field of 2.8 mG, a synchrotron age of $\lesssim1.8\times10^{3}$ yr, and a time-averaged jet power of ${\sim}5\times10^{41}$ $-$ $5\times10^{44}$ erg s$^{-1}$ $-$ are characteristic of compact steep-spectrum and GPS young radio galaxies, not of canonical radio-quiet AGN. The two-component structure admits two interpretations that the present data cannot distinguish: the extended emission may be the growing lobe of a genuinely young, expanding radio galaxy, or relic plasma from an earlier episode of a transient or recurrent jet. Under either, H 0557$-$385 is better understood as an intermediate object: optically a Seyfert, but with the radio-physical properties of a newly ignited or recently re-triggered radio galaxy. It is therefore a candidate missing link between radio-quiet AGN and large-scale radio galaxies. Distinguishing these scenarios will require high-resolution imaging and multi-epoch monitoring
We present new Chandra observations of seven broad-line AGNs in low-mass galaxies ($M_\star < 5 \times 10^9\,M_\odot$) selected from the GAMA sample of Salehirad et al. (2022). X-ray emission is detected in six galaxies, with luminosities spanning $\log(L_{\rm 0.5-8\,keV}/{\rm erg\,s^{-1}})\approx40.5$--43.8. Their X-ray luminosities generally exceed predictions for X-ray binary populations, and their proximity to the optical galaxy nuclei favors accreting massive black holes as the dominant emission source. Spectral fits for four sources yield photon indices $\Gamma\approx1.7$--2.2, with little evidence for intrinsic absorption in most cases. Virial black hole masses and hard X-ray bolometric corrections imply nominal Eddington ratios $\lambda_{\rm Edd}\approx0.004$--1.1, although uncertainties are substantial. Optical tracers generally imply higher bolometric luminosities and Eddington ratios, particularly for the X-ray-undetected galaxy. The X-ray-bright sources are broadly consistent with optical AGN scaling relations involving H$\alpha$ and [O III], whereas most lie below the established X-ray--mid-infrared relation, potentially reflecting host-galaxy contamination. Four sources are consistent with the expected UV-to-X-ray spectral slope relation, while three show evidence for relative X-ray weakness. These results reveal diverse X-ray properties among broad-line AGNs in low-mass galaxies and highlight the importance of multiwavelength diagnostics for understanding black hole accretion and interpreting broad-line AGN candidates at high redshift.
The lower level of the He I $\lambda$10830 transition is metastable and therefore well populated. In H II regions, the line can become optically thick, and its photons then undergo resonant scattering. Draine (2026) predicted that scattering splits the profile into several peaks. We present Magellan/WINERED spectra ($R \approx 70{,}000$) at six pointings along a line from the ionizing source CEN 1 across the southwestern bar of M17, with He I $\lambda$10830 and Pa$\gamma$ in the same exposures. Every He I $\lambda$10830 profile is multi-peaked, while the Pa$\gamma$ profiles are single-peaked. Because Pa$\gamma$ does not undergo resonant scattering, it traces gas kinematics; its single peak argues against a purely kinematic origin of the He I peaks, and the shared exposures exclude an instrumental origin. We therefore attribute the He I peaks to resonant scattering, as predicted. We compare the profiles quantitatively with the static, spherically symmetric models of Draine (2026), using width and asymmetry measures independent of the systemic velocity. At two pointings far from CEN 1, no static model of any optical depth reproduces width and asymmetry together: both profiles are more red-weighted than static models of comparable width. Such profiles cannot arise from uniform motion but are expected from scattering in expanding gas. We argue that the profile is shaped by both the kinematics and the optical depth of the He$^{+}$ zone, and resolved He I $\lambda$10830 profiles could therefore provide a new diagnostic of these properties in H II regions.
Carbon radio recombination lines (CRRLs) arising from the cold neutral medium (CNM) of the interstellar medium are potential foregrounds in the 1-50 MHz band that LuSEE-Night will observe from the lunar far side. CRRLs are sensitive probes of the temperature, density, and radiation field of the CNM, and LuSEE-Night will provide sky-averaged measurements in a poorly explored frequency range. We model CRRLs across this band, accounting for doppler, collisional, and radiation broadening, and we estimate line strengths using two independent methods - fixing either the peak or the frequency-integrated optical depth - applied both uniformly across the sky and with region-dependent values informed by prior low-frequency observations. We simulate LuSEE-Night's expected response to these CRRLs and further convolve the beam-diluted spectra with LuSEE-Night's polyphase-filter-bank spectrometer response, including its zoomed-mode frequency resolution of $\sim$390 Hz, to obtain the expected observed brightness temperature. Using these simulated spectra, we estimate the integration time required to detect individual CRRLs at SNR=5 across the six sky models considered. Required integration times range from as short as 30 hours (in the most optimistic model where the optical depth across the sky is $\sim$10$^{-3}$) to 27.6 years (in the most conservative models where the optical depth across the sky is $\sim$10$^{-4}$). Stacking the 361 simulated C$\alpha$ lines between 10 and 50 MHz reduces the integration time needed for an SNR=5 detection to $\sim$11 minutes and $\sim$151 hours respectively, indicating that LuSEE-Night has realistic chances of making a stacked detection of C$\alpha$ RRLs within a realistic mission lifetime, even under the most conservative optical-depth assumptions.
Radio jets deposit energy into the interstellar medium of their host galaxies, and while a jet is still confined within the host it is expected to drive shocks through the gas. Broad [OIII] 5007 profiles trace ionized gas that has been disturbed, the [OI]/H-alpha versus [OIII]/H-beta diagram helps distinguish gas photoionized by an AGN from gas excited by shocks, and the high ionization [NeV] 3426 line traces the hard UV continuum of the accretion disk, which shocks only reproduce at very high velocities. We have selected two samples of radio-loud AGN from a cross-match of the VLA Sky Survey with DESI Data Release 1, at 0.15 < z < 0.5 and with [OI] 6300 detected at > 5-sigma: one with projected radio sizes of 10-15 kpc, whose jets are still inside the host, and one with sizes greater than 25 kpc, whose jets have broken out. We fit the [OIII] and [OI] profiles, measure W80, and classify each source on the BPT diagram. The confined sources have broader [OIII] lines, sit systematically closer to the LINER region, and are detected less often in [NeV], and the [NeV] difference is not explained by redshift or dust. The broad components are not systematically blueshifted, so the confined sources are distinguished by line width rather than by outflow velocity. We then discuss how these results indicate that the jets of the confined sources are driving strong shocks through the interstellar medium of their hosts.
This article presents an overview of key scientific challenges in the astrophysics and astrochemistry of the interstellar and intergalactic media. Addressing many of these challenges will become possible with the Russian space observatory Spektr-UF, which is currently being prepared for launch. The ultraviolet (UV) spectral range is critically important for studying the evolution of the Universe, as it contains fundamental absorption and emission lines of most chemical elements and the most important molecules. These lines make it possible to reliably determine the physical conditions and chemical composition of various astrophysical objects, as well as the characteristics of the processes occurring within them. The article examines the prospects for UV observations across a broad range of scientific problems, from investigating the epoch of helium reionization and the thermal history of the Universe to mapping ongoing star formation in galaxies. Dedicated sections address the study of the chemical evolution of galaxies at intermediate redshifts, the distribution of "hidden" baryons and metals, the small-scale structure of interstellar clouds, the physics of photodissociation regions and protoplanetary disks, and the modeling of UV emission from nebulae surrounding fast-moving pulsars. The high sensitivity and spectral resolution of the Spektr-UF instruments are expected to provide fundamentally new data across all these research areas, filling existing gaps in our understanding of the interstellar and intergalactic media.
We here present the first ever mass-metallicity relation (MZR) of fossil disk populations using the resolved stellar populations in the James Webb Space Telescope Near-Infrared Camera (JWST/NIRCam) images of six nearby galaxies. Both the mass and metallicity were determined using the Red Giant Branch (RGB) stars, employing methods that have been well established to study the halo populations of nearby galaxies using the Hubble Space Telescope images. Specifically, we obtained the mass and metallicity by comparing the color, magnitude and number density near the tip of the RGB (TRGB) stars in the F115W$-$F200W vs F200W color-magnitude diagrams (CMDs) with that of the PARSEC isochrones of 4 and 13~Gyr. The RGB metallicities of the disks of nearby galaxies closely match those found in galaxies at redshifts $z>8$, with the metallicity range following a power-law relation with the fossil disk mass. The power-law index of the fossil disk MZR, $\gamma\approx0.26$, compares well with the typical value found in MZRs obtained using gas metallicities across redshifts. Through this work, we illustrate the utility of JWST/NIRCam images for obtaining the mass and metallicity of the fossil disks of nearby galaxies at precisions that were not possible earlier, which opens up a new method to carry out the near-field cosmological studies.
The corotation radius R_CR of a spiral galaxy marks the radius where the angular speed of the spiral pattern matches the orbital speed of the disk material. Despite its importance for understanding spiral structure and galaxy evolution, very few galaxies have corotation measurements, often derived using heterogeneous techniques. We present an automated photometric pipeline that identifies corotation radii by tracking the azimuthal phase offset between young and old stellar populations. Building on the color-gradient framework of \citet{Puerari1997}, we extract azimuthal brightness profiles from deprojected dual-band images, fit periodic models to the profiles, and identify corotation candidates at radii where the phase difference between the two stellar tracers changes sign. Each candidate is assigned an adaptive uncertainty interval and reported with a goodness-of-fit metric. We benchmark the method against a cross-method literature compilation, scoring every technique -- including our own -- against a reference built from the published measurements alone and evaluated leave-one-out. Over the $90$ galaxies for which such a reference exists, the pipeline places a correct corotation radius in $80.0\%$ of them, recovers $63.6\%$ of their known corotation radii, and reaches a harmonic mean of recall and purity of $0.58$, the highest values of any method in the comparison. Unlike the published methods, each of which was applied to a small, curated set of galaxies, our pipeline is run on the entire reference sample without any pre-selection, a sample two to six times larger than existing methods. The pipeline is scalable to large surveys, flexible with respect to spiral mode, and naturally recovers multiple corotation radii in galaxies with complex spiral structure, providing a uniform framework for studying disk resonances across diverse galaxy populations.
The vertical distribution of molecular gas in the Milky Way disk is poorly studied, especially in the 4th quadrant and the far side of the Galaxy. While surveys over 20 years ago suffered from coarse beam and non-Nyquist sampling, most of the recent surveys are limited to $|b|<1^\circ$ and/or focus on the Northern Galactic plane. We examine the molecular gas's vertical distribution and properties in the fourth quadrant to check the impact of Galactic structure on current star formation. We mapped two arm tangent regions ($l=[329^\circ.0,327^\circ.0]$ for the Norma-Outer arm, and $l=[310^\circ.0,308^\circ.5]$ for the Scutum-Centaurus arm) with the $^{12}$CO 3-2 line using the 7-pixel LASMA receiver of the APEX 12 m telescope, covering up to $b=[-2^\circ,+2^\circ]$ (or $|z|\sim200$ pc near the tangent points). The noise level of the $^{12}$CO 3-2 line is about 0.4 K [$T_{MB}$] in velocity channels of 0.5 km s$^{-1}$. The vertical distribution around the tangent regions of the spiral arm is fitted with two Gaussian components, the narrow one with an FWHM thickness of 25 pc and the wide one of about 100 pc. Two explanations are proposed: they are two sub-components of the thin disk (the narrowest tracing the spiral arm and the other the inter arms components), or they trace both thin and thick disks that show a smaller thickness when observed with CO 3-2 than when observed with CO 1-0. The latter indicates that the density distribution of the interstellar medium exhibits a steeper gradient at larger heights above the plane. Clumps in the two tangent regions are searched and divided into groups by relative height. Compared with the low relative height clumps ($|z|<50$ pc), the median relative height clumps ($50~\mathrm{pc}<|z|<100~\mathrm{pc}$) have lower excitation temperature and surface density, with fewer high values in the distribution. A similar tentative trend is found for the mass.
Satellite dwarf galaxies are reshaped by the tidal field of their host, a process that may account for part of the structural diversity of the observed dwarf population. We study how the stellar component of a satellite responds to tidal stripping using a suite of 480 controlled $N$-body simulations of satellite galaxies consisting of both dark matter (DM) and stars orbiting a Milky-Way-mass host. The simulated dwarfs span a broad range of DM halo structural and stellar-distribution parameters, including halo concentration, inner density slope, stellar-to-halo mass ratio, compactness of the stellar distribution with respect to the halo, as well as the S\'ersic index of the stellar profiles. We present a comprehensive library of tidal tracks, namely, the evolution of the stellar mass, half-mass radius, mean surface density, and line-of-sight velocity dispersion, as functions of the bound mass fraction of the hosting DM subhalo, and provide simple and accurate fitting functions. We also identify the dependence of tidal tracks on key factors in the initial structural conditions. Notably, stellar compactness determines the duration over which the stellar mass remains relatively intact while the surrounding DM is being stripped. The S\'ersic index and inner DM slope, in turn, govern the late-stage stellar mass-loss slope and the contraction or expansion of the remnant. Our simulations and empirical models provide a framework for modelling the stellar evolution of satellites across a broad range of progenitor structures, useful for semi-analytical models of satellite galaxy evolution.
Previous studies of dust emission in M31 based primarily on Herschel data have reported inconsistent radial trends in the dust emissivity index ($\beta$), partly due to limited wavelength coverage and the intrinsic $T_{\rm dust}$-$\beta$ degeneracy. We aim to improve the constraints of $\beta$ determinations and obtain the spatial surface density and temperature distributions at GMC scales in M31 by extending the spectral coverage into the millimeter regime and by quantifying the impact of wavelength coverage on the $T_{\rm dust}$-$\beta$ degeneracy. We present new IRAM 30m NIKA2 1.15 mm observations along the minor axis of M31 at an angular resolution of 11 arcsec, corresponding to $\sim 40$ pc at the distance of M31. These data are used with Herschel and JCMT SCUBA-2 maps to perform pixel-by-pixel single-component modified blackbody fitting. Including the 850 $\mu$m and 1.15 mm data helps reduce the $T_{\rm dust}$-$\beta$ degeneracy and yields an average emissivity index of $\beta \approx 1.8$, systematically lower than values derived from far-infrared-only analyses. Radial analysis shows higher $\beta$ values in the 5 kpc ring compared to the 10 kpc ring. The elevated $\beta$ values in the inner 5 kpc may be linked to changes in dust composition, potentially associated with enhanced starlight heating in this region. Millimeter wavelength coverage is important for improving $\beta$ constraints in M31. The lower $\beta$ values inferred from the 250--1150 $\mu$m SED fitting suggest possible variations in dust emissivity and highlight the importance of sampling the long-wavelength SED slope in nearby galaxies.
Overlapping blind 21 cm and wide-area low-frequency continuum surveys make it possible to measure which radio sources an untargeted HI survey recovers. Cross-matching FASHI DR1 with the LoTSS DR2 value-added catalog yields 4392 one-to-one associations. Within an empirically defined comparison region of $2912$\,deg$^2$, we construct a low-redshift, spectroscopic, radio-selected parent of 25,573 LoTSS sources whose expected HI line falls in the FASHI band, and measure how often each is recovered. Sources classified as radio-loud AGN in the published LoTSS DR2 radio-AGN classification are recovered less often than star-forming ones: 143 of 1542 ($9.27\%$, $7.87$--$10.83$) against $14.88\%$ ($14.43$--$15.33$) of 24,031, an odds ratio of $0.585$ ($0.491$--$0.697$). The two classes, however, differ strongly in host properties, by $1.34$ dex in median specific star formation rate, and within their overlapping stellar-mass and star-formation ranges we detect no statistically significant residual class difference (adjusted odds ratio $1.60$, $0.87$--$2.94$). In contrast, 144 MHz luminosity remains positively associated with HI recovery after adjustment for the measured host properties, redshift and an approximate sensitivity proxy: within the same overlapping range, each dex raises the odds of recovery by a factor of $2.03$ ($1.54$--$2.68$), an association carried primarily by the star-forming population, not by the radio-AGN subsample. We interpret this as an empirical relationship with detectable HI emission, not as evidence that radio activity increases or decreases HI mass. The association catalog and the controlled recovery measurements characterize the radio population sampled by a blind HI survey.
We present a systematic study of the faint outer light profiles of star-forming galaxies using deep JWST/NIRCam imaging from the CEERS, JADES, and PRIMER surveys. Our sample consists of 14,812 face-on disk galaxies at $1<z<9$ with $\log(M_*/M_{\odot})>8.5$, selected from the DAWN JWST Archive. To characterize the low-surface-brightness outskirts beyond the effective radius ($R_e$), we stack galaxies in bins of stellar mass and redshift, accounting for cosmological surface-brightness dimming, angular-size scaling, and PSF convolution, and estimate residual backgrounds from blank-sky stacks. The color profiles generally become bluer toward larger radii, indicating negative color gradients and supporting an inside-out growth scenario. Galaxies with $\log(M_*/M_{\odot}) < 9.5$ at $z>2.5$ exhibit a weak reversal in their outermost regions, suggesting more complex stellar population gradients at early times. The outer light profiles generally exhibit a good exponential decline with radius, and the outer scale lengths measured beyond $2R_e$ show mass and redshift dependences remarkably similar to those of the conventional mass-size relation. This similarity suggests that the extended outer light is closely linked to the same processes governing the growth of the inner galaxy, rather than providing a direct tracer of ex-situ stellar components in the early universe. We also find little wavelength dependence in the outer scale lengths, indicating that dust attenuation likely has a limited impact at these radii. These results provide new constraints on the buildup of extended stellar distributions during cosmic noon and at earlier epochs.
We investigate the wavelength dependence of disc scale lengths in galaxies from the TNG50-SKIRT Atlas (TSA), and assess whether the simulated galaxies reproduce the structural properties and scaling relations observed in real galaxies. We measure disc scale lengths from 1D radial surface-brightness profiles of multi-wavelength synthetic images. The disc-dominated region is defined interactively per galaxy and applied consistently across bands. We restrict the analysis to nearly face-on, star-forming galaxies and retain only systems whose r-band profiles are well described by an exponential model. The resulting scale lengths are compared to observational samples and analysed using both dust-attenuated and dust-free images, as well as intrinsic stellar population maps. We find that the majority of TSA galaxies exhibit exponential discs in realistic mock observations. TSA galaxies reproduce the observed disc scale length-stellar mass (luminosity) relation, but are systematically larger at fixed mass or luminosity. The dependence of disc scale length on morphology is weak. Disc scale lengths correlate strongly across wavelengths, but decrease systematically with increasing wavelength. When normalised by the stellar-mass scale length, TSA galaxies exhibit a monotonic trend consistent with observations over the optical-to-NIR range. Comparing dust-free and dust-attenuated images and linking the results to intrinsic galaxy properties, we find that stellar population gradients are the primary driver of this wavelength dependence. In particular, radial gradients in stellar age dominate the effect, while metallicity gradients play a secondary role. Dust attenuation further enhances the wavelength dependence at short wavelengths but is not its main origin. Residual offsets in absolute scale length indicate the remaining differences between simulated and observed galaxy structure.
We present the low-frequency GAMA-23 field of the Galaxy and Mass Assembly (GAMA) survey with upgraded Giant Meterwave Radio Telescope (uGMRT) observations in Band-2 ($120-250$ MHz). The on-source observation was conducted for ${\sim}5$ hours. The final image achieved an off-source RMS noise of 320 $\mu$Jy beam$^{-1}$, covering an area of $5.86\,\text{deg}^2$ with restoring beam size of $15.4''{\times}8.2''$ at the central frequency of 183 MHz. The catalogue derived from the radio image includes 569 sources with a flux density limit of ${\geq}\,5{\sigma}$. The flux density measurements and the positional accuracy are cross-verified and compared with other radio catalogues available in the literature. The spectral indices derived from fitting a power law are -0.68$^{+0.18}_{-0.23}$ for the ASKAP EMU catalogue and -0.72$^{+0.19}_{-0.24}$ for the NVSS catalogue. The normalised source count derived from this catalogue is consistent with models and observations with a nominal catalogue threshold of 1.7 mJy, while the sensitivity varies across the image.
Although a set of polycyclic aromatic hydrocarbons (PAHs) has recently been identified in the cold dark cloud TMC-1, several common PAH motifs remain absent, leaving the origin of this apparent structural selectivity unresolved. Triphenylene (\ce{C18H12}) provides a stringent test of whether relative thermodynamic stability alone can account for the emerging PAH inventory because it is the smallest fully benzenoid PAH predicted by Clar's rule, is exceptionally stable, and is a key subunit of larger detected aromatic frameworks such as coronene and fullerene-related species. To probe whether such thermodynamically favored carbon skeletons are selected under cold interstellar conditions, we synthesized cyanotriphenylenes and measured their first 6.5--16~GHz microwave rotational spectra as polar tracers for the non-polar parent. An astronomical search based on these spectroscopic parameters yielded no detection, suggesting a possible ``missing triphenylene'' anomaly: despite its exceptional thermodynamic stability, this fully benzenoid PAH may be relatively depleted in TMC-1. To rationalize this behavior, we introduce a ring-node graphic representation that classifies PAH skeletons by topology; within this framework, triphenylene, whose compactness is otherwise ambiguous, is classified as non-compact. This representation reveals a tentative clustering of the currently detected and undetected PAHs according to topology, suggesting that the current PAH inventory cannot be rationalized solely on the basis of thermodynamic stability and may instead reflect differences in formation and destruction kinetics. The observed selectivity may arise from two complementary effects: sequential growth decay along bottom-up growth pathways and rapid consumption of bay-region intermediates by reactive unsaturated small species.
Canes Venatici I (CVnI) is a distant Milky Way (MW) dwarf spheroidal (dSph) satellite. To date, there is no consensus on its evolution and the properties of its stellar population. This work is aimed at obtaining an accurate picture of the star formation history (SFH) and metallicity distribution of CVnI to reconstruct its evolution in detail, as well as to infer the possible effects of internal and external feedback. We used archival HST/ACS observations to obtain the deepest colour-magnitude diagram (CMD) to date, reaching $\sim$2 mag below the old main sequence turn-off. We derived the SFH and metallicity distribution of CVnI using a state-of-the-art CMD-fitting technique. We found that the SFH is dominated by a single star formation period, which peaked around 11.8 Gyr ago, well after the reionisation epoch, and remained active until $\sim$10.4 Gyr ago. The galaxy's global metallicity, [Z/H], ranges from -2.4 to -1.5 dex. Interestingly, while its star population is old and metal-poor, compared to other MW satellites of a similar size and luminosity that formed most of their stars in a single burst, CVnI experienced a delayed star formation period. We carried out an exhaustive set of tests with synthetic and real populations to ensure the reliability of these results. We suggest that the evolution of CVnI could have been regulated by its mass accretion history. The galaxy would have evolved above (but still close to) a theoretic redshift-dependent critical mass above which it is possible to maintain star formation. The combined effect of SN feedback would have made CVnI's halo mass subcritical at z$\approx$2, definitively quenching its star formation. We cannot rule out the possible influence of gravitational interaction of CVnI with the MW at early ages, as hinted at by the most recent calculations of its orbit.
This study analyzes spectra from the central region of the galaxy cluster Abell 85 observed with GTC/OSIRIS, focusing on the cD galaxy Holm 15A and the point-like X-ray source SDSS J004150.75-091824.3, projected $13.74\arcsec$ from Holm 15A. For the latter, we found it is a background quasar with a redshift of $1.56386 \pm 0.00397$, ruling out the possibility of it being a rogue BH gravitationally bound to Holm 15A. In addition, using single-epoch spectroscopy, we report that the quasar J004150 hosts a Supermassive Black Hole (SMBH) with a mass of $\log(M_{\text{BH}}/\mathrm{M_{\odot}}) = 8.72 \pm 0.26$.
Radiative-transfer models of supermassive black holes accreting inside dense gas cocoons reproduce the X-ray-to-near-infrared spectral energy distribution of "little red dots" (LRDs) using the code Sirocco. In the ultraviolet, these models also predict weak broad emission lines and a series of metal absorption lines, which deep spectroscopy from the JWST SPURS survey now detects in several LRDs. Here we use the models to interpret these features. We find that N and C ions of equal charge (3+ or 2+) occupy largely the same gas in the simulations, such that the combination of the broad N IV]/C IV and N III]/C III] flux ratios simultaneously constrains both the electron density and the N/C abundance ratio of the gas in the LRD proper. The nitrogen and carbon emission of SPURS-GN-2, an LRD at $z=7.19$, requires an order of magnitude nitrogen excess compared to the solar value, N/C $= 12^{+3}_{-2}$ (N/C)$_\odot$, in the broad-line gas with electron density $\log n_e = 9.7^{+0.3}_{-0.5}$ cm$^{-3}$. Thus, around half the broad-line CNO nuclei have passed through hydrogen burning. Because the ionised gas is replaced on a century timescale, sustaining this enrichment favours gas recycling. UV absorption lines test this independently. In two of the four LRDs, line blueshift velocities clearly increase with the photon energy required to ionise the absorber gas. In the models the absorption lines are spatially stratified, indicating that the gas is launched near the escape speed and slowed by gravity. In GN-2, where the measurement can be made, the inferred deceleration requires radiation pressure close to the Eddington limit of a $10^{6-7}$ M$_\odot$ black hole. The lines are also typically strongly saturated, making inferences of direct abundance ratios misleading.
The orientation of a dusty torus within a unified model explains the presence (Type-1) or absence (Type-2) of broad emission lines in Active Galactic Nuclei (AGN) spectra. This orientation-based unified model, however, fails to explain differences in host galaxy properties, such as star formation rates, of Type-1 and Type-2 AGNs. Star-formation histories (SFHs) can shed light on the connection between AGN type and host galaxy properties, but are challenging to extract from Type-1 AGN that outshine their host galaxies. We use mean-field independent component analysis (MFICA) spectrum decomposition to extract the stellar populations of $\sim$3000 optically selected Type-1 and Type-2 AGN host galaxies from the seventh data release (DR7) of the Sloan Digital Sky Survey (SDSS), matched in redshift ($0.16 \leq z \leq 0.4$) and AGN luminosity ($6.5<\log_{10} [L_{[OIII]}/L_\odot] <9.5$). Using MFICA, we find that only $\sim$10 per cent of AGN host galaxies have recently ($\lesssim1$\,Gyr) and rapidly quenched star formation following a starburst, with Type-2 AGN host galaxies having done so at most 100\,Myrs more recently than Type-1 AGN host galaxies. For most ($\sim$90 per cent) AGN hosts with normal recent star formation histories, Type-2 AGNs are associated with slightly younger stellar populations than Type-1 AGNs. The younger stellar populations of Type-2 AGN hosts can be explained by a link between dusty torus covering factors and stellar populations, by host-galaxy obscuration of AGN, or by an evolution in AGN type without major bursts or rapid quenching of star formation.
Super-critical accretion onto stellar-mass compact objects is sometimes revealed by ultraluminous X-ray sources (ULXs). In other cases, X-rays are heavily obscured along our line of sight, but a super-Eddington accretion power can be indirectly revealed by multiband studies. We have identified a candidate super-critical source in NGC 5408 (labelled X-2). We argue that: it is powered by accretion; it is among the most powerful in the local universe, despite its apparent X-ray faintness; it has exceptional optical properties (both in the continuum and in the lines). We carried out a multiband imaging and spectral study with the ATCA, the VLA, HST, the VLT and Chandra. We found an unresolved source with: variable radio emission (5-GHz luminosity of a few x 10^{35} erg/s); red optical continuum with absolute mag M_{V,0} = -9.1, M_{I,0} = -10.6; exceptionally broad low-ionization emission lines (FWHM ~ 1700 km/s) with P-Cygni profiles; narrow, photoionized emission lines including strong He II 4686; point-like hard X-rays; marginally resolved soft X-rays. We also found an ~20-pc He^{++} nebula near X-2, associated with candidate Wolf-Rayet stars. The optical continuum declined by 2 mag between 2010 and 2024, as did the intensity of broad and narrow lines. We argue that the system is powered by the radiative and mechanical output of a super-Eddington stellar mass BH, with an accretion power >~10^{40} erg/s. We propose that X-2 is a Compton-thick ULX seen at high inclination, with a flaring jet and X-ray emission emerging from the polar funnel. We argue that the optical continuum and the broad emission lines are signatures of an optically thick outflow, launched either from the accretion disk, or from an LBV-like donor star, or, more speculatively, caused by the elusive phase of common envelope ejection. We suggest that we are looking at a short-lived phase of hyper-Eddington accretion.
The strong nitrogen (N) features observed in high-redshift galaxies, such as GN-z11, with JWST point to an efficient source of N production in the early Universe. Very massive stars (VMSs) are promising candidates owing to their strong winds and large convective cores of CNO-processed material. Whether massive-star surfaces in general become N-enriched depends on the interplay of convective-boundary mixing (overshooting), rotation, and mass loss, which remains poorly constrained. Using a grid of MESA evolutionary models, we isolate the overshooting and rotation channels at $40$, $100$, and $200\,M_\odot$ and investigate how these channels bring N-rich material to the surface of massive and very massive stars as a function of initial mass and metallicity. We also construct a synthetic Large Magellanic Cloud (LMC) population based on a larger initial mass grid ranging from $20-300\,M_\odot$ for comparison with the observed N-enriched fraction. VMS surface enrichment is remarkably robust across cosmic metallicity. At lower metallicities, wind stripping is weaker and the overshooting channel shuts off entirely, yet a modest amount of rotation of $\sim90\,\mathrm{km\,s^{-1}}$ alone still enriches the surface. At higher metallicity, stronger winds dominate and uncover the core almost independently of the adopted mixing. The two channels operate through physically distinct mechanisms: overshooting enriches the surface only once winds strip the envelope down into the N-rich layers left by the receding core, giving an abrupt jump. Rotation, by contrast, mixes N outward continuously through the layers above the core, producing a gradual rise. Applied to the LMC, a population with modest rotation drawn from the observed velocity distribution and modest overshooting reproduces the observed N-enriched fraction without large core boundary mixing efficiencies otherwise required by non-rotating models.
We report the discovery of the Seyfert galaxy J234728.73+242745.7 as a recurrent intermediate-type CLAGN with extreme optical/UV variability. Optical spectra spanning nearly three decades reveal Type 1.0$\rightarrow$1.5$\rightarrow$1.2 transitions, accompanied by the disappearance and reappearance of broad He II $\lambda4686$ and a broad-line Balmer decrement evolving from 4.5 to 7.2 and then 2.4. Monitoring reveals coordinated variability from X-rays to the MIR. SED decomposition yields a host-corrected g-band high-to-low-state flux ratio of $5.4\pm0.4$, exceeding the Swift/XRT ratio of $2.7\pm0.8$ across the changing-look transition. This discrepancy may arise from reduced dust extinction, as correcting for the low-state continuum reddening ($A_V^{\rm cont}=0.66\pm0.23$ mag) brings the optical/UV ratios close to the X-ray value, although the correction is model-dependent and intrinsically weaker X-ray variability may also contribute. However, X-ray spectra show no compelling evidence for intrinsic gas absorption or its variability ($N_{\rm H}^{\rm intr}\lesssim5\times10^{20}$ cm$^{-2}$). In contrast, EP/WXT monitoring during the recent high state reveals order-of-magnitude X-ray fluctuations on monthly-to-sub-year timescales, exceeding contemporaneous optical variations. Meanwhile, the radio flux density remains stable at $\sim2$ mJy across all ASKAP observations since mid-2020. Together with optical/UV and MIR variability and the broad He II transition, these results favor intrinsic accretion-state changes as the primary driver, while allowing a secondary contribution from variable obscuration. The source displays a loop-like MIR color--magnitude evolution, likely driven by the delayed response of an extended torus. This recurrent CLAGN offers a laboratory for probing the dynamic response of the broad-line region and circumnuclear dust to accretion-state transitions.
Gaia22alz (nova Vel 2022) shows characteristic properties in its light curves and spectral evolution similar to slow novae HR Del, V723 Cas, and V5558 Sgr. Their outburst begins in a way of hydrostatic expansion with no mass loss, followed by large amplitude ($\Delta V \sim 2$ mag) multiple peaks around the mean magnitude of $M_V \sim -5.5$, and eventually it decays similarly to normal classical novae. We present a light curve model of Gaia22alz based on our metamorphic nova theory: a nova starts from a static expansion and then metamorphoses to an optically thick wind evolution through a large amplitude multiple peak phase as a violent relaxation process. Our theoretical light curve for the rising phase consistently explains the slow rise and early spectral evolution of Gaia22alz. Gaia22als is a close binary as well as other three novae, which is consistent with our metamorphic nova theory that the companion motion in the nova envelope triggers the metamorphic transition. Our results do not support E. Aydi et al.'s explanation that the slow optical rise of Gaia22alz is owing to the irradiation of X-ray/UV flash.