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Physics Astrophysics Astrophysics of Galaxies

astro-ph.GA Watch Astrophysics of Galaxies

Tuesday 13 October · still arriving

Astrophysics of Galaxies

MUSE-DARK IV. Comparing Dark Matter Densities to Star Formation Histories in 375 intermediate-z galaxies

B. I. Ciocan, N. F. Bouché, J. Fensch et al. (+5 more)

(Abridged) Baryonic feedback is expected to transform cuspy dark-matter (DM) haloes into cores, but direct observational links between inner DM slopes and galaxy star-formation histories (SFHs) remain limited. We investigate and quantify the connection between halo inner slopes and baryonic assembly histories in a large sample of intermediate-z galaxies. We analyse 375 galaxies at 0.1<z<1.43 spanning 7<log(Mstar/Msun)<11.2 using 3D forward modelling of MUSE kinematics and disk-halo decompositions with mass-dependent (DC14-based) and generalised Navarro-Frenk-White (gNFW) halo profiles. Stellar population parameters are inferred from multi-band Spectral Energy Distribution fitting of UV-to-MIR photometry using a non-parametric SFH model. Bayesian model comparison shows that the DC14-based halo density profiles are statistically preferred over gNFW for a substantial fraction of the sample. The inferred inner slopes from gNFW fits nevertheless follow the DC14 expectation and reproduce the expected dependence on the stellar-to-halo mass ratio, despite this not being explicitly imposed. Partial correlation coefficient and random forest regression analyses consistently identify stellar mass (or, equivalently, the stellar-to-halo mass ratio) as the primary driver of the inner density slope, a result that holds robustly even when the analysis is restricted to the gNFW fits. In contrast, SFH-related quantities (e.g. formation time and 'burstiness' indicators) exhibit no independent predictive power on the DM halo inner slope once the dependence on stellar mass is accounted for. Cored systems preferentially occupy lower-mass, more bursty bins with later assembly times, whereas cuspy systems are associated with higher stellar masses, lower star formation activity, and earlier assembly epochs, in agreement with theoretical expectations of stellar-feedback-induced cores.
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All authors B. I. Ciocan, N. F. Bouché, J. Fensch, D. Krajnović, J. Freundlich, H. Desmond, A. Jeanneau, B. Famaey

Astrophysics of Galaxies · Cross-listed from physics.chem-ph

Extrapolating Collisional Rate Coefficients for Molecules of Astrophysical Interest Using Neural Networks

Yigit Ergen and Jérôme Loreau

State-to-state rate coefficients for inelastic molecular collisions are essential inputs for non-local thermodynamic equilibrium radiative transfer models, yet their computation using quantum scattering methods is prohibitive for large molecules and highly excited rotational states. We investigate the ability of artificial neural networks to extend existing datasets of collisional excitation rate coefficients without performing additional scattering calculations. A multilayer perceptron model was trained using molecular quantum numbers, level energies, energy gaps, and kinetic temperature as descriptors, and optimized on logarithmic rate coefficients. The model was tested on diverse collision systems ranging from simple diatomic molecules (CO, SiO) to open-shell species (SO), small asymmetric tops (H$_2$O, SO$_2$), and complex organic molecules (benzonitrile and vinyl cyanide) colliding with H$_2$ molecules or He atoms. Extrapolations were performed toward higher rotational levels, higher temperatures, and combinations of both. For most systems, predictions of rate coefficients involving previously unseen rotational states yielded mean error factors between 1.1 and 1.5, with the dominant rate coefficients generally reproduced more accurately than weaker transitions. Temperature extrapolations proved particularly successful, while combined extrapolations in temperature and rotational levels remained accurate to within a factor of two in most cases. The prediction quality depends on the interplay between dataset size, temperature range, molecular complexity, and the presence of clear collisional propensity rules. Overall, the approach demonstrates that machine learning can provide a practical route to extending collisional datasets for astrophysical applications, especially for large molecules for which additional quantum-scattering calculations are computationally demanding.
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Astrophysics of Galaxies

Massive black holes in the first billion years with JWST

Hannah Übler

The James Webb Space Telescope has unlocked uncharted territory for the study of early black holes, enabling the detection of fainter and smaller black holes at larger cosmological distances than previously possible. Compared to nearby massive black holes, they are characterised by several unexpected attributes, such as their multi-wavelength properties or their relation to their host galaxies. These observational findings challenge our understanding of the past evolution of present-day supermassive black holes, and provide novel anchor points to constrain theoretical models of black hole formation and growth. This review summarises our current understanding of the observed properties of newly discovered, active black holes in the early Universe, discusses the status of mass measurements and the relation to their hosts, as well as open questions and future prospects.
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Astrophysics of Galaxies · Cross-listed from astro-ph.HE

Low-frequency spectra and scattering of pulsars towards the Gum Nebula with the MWA

Ting Yu, Zhifu Gao, Zhongli Zhang et al. (+1 more)

Context. The Gum Nebula is a nearby ionised complex with sight-line-dependent pulsar propagation. Aims. We test whether a smooth ionised structure can explain low-frequency spectral turnovers and pulse broadening, or whether smaller-scale material is required. Methods. We analysed Murchison Widefield Array observations of six pulsars at 80–240 MHz, combining sub-band flux densities with literature data. We compared power-law, free–free absorption (FFA), and turnover-constrained broken-power-law (BPL) spectra, and modelled scattering through pulse-profile convolution. PSR J0820-4114 and the Vela pulsar were fitted jointly across frequency. Results. All six spectra depart from a single power law. FFA is favoured for PSRs J0737-3039A and J0820-4114, and BPL for J0742-2822 and J0835-4510; the other two classifications depend on assumed error floors. Conditional FFA solutions imply emission measures of $10^4$–$10^5$ pc cm$^{-6}$ for electron temperatures of $3\times10^3$–$10^4$ K, far exceeding smooth-shell expectations. PSRs J0737-3039A and J0837-4135 have scattering laws consistent with $\tau_{\rm sc}\propto\nu^{-4}$. We obtain $\alpha_{\rm sc}=-3.07\pm0.11$ for J0742-2822 and $-1.59\pm0.44$ for J0820-4114 using a joint two-component model. The Vela pulsar is best described by an effective thick-screen model with $\alpha_{\rm sc}\simeq-2.74$. Neither tested Galactic electron-density model reproduces both independent distances and low-frequency scattering uniformly. Conclusions. The results favour a structured Gum–Vela magneto-ionic environment in which neighbouring sight lines probe different absorbing and scattering material; these effects need not arise in the same plasma component.
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All authors Ting Yu, Zhifu Gao, Zhongli Zhang, Weicong Jing

Astrophysics of Galaxies

Radio ghosts: Radio polarimetry study of newly discovered cluster minihalo candidates or radio tailed galaxies

Sam Taziaux, Christopher J. Riseley, Stefan W. Duchesne et al. (+5 more)

Extended diffuse radio emission in the central regions of galaxy clusters is commonly associated with non-thermal processes in the intracluster medium (ICM), but its origin and the mechanisms responsible for sustaining it remain uncertain. We present the discovery and multi-wavelength analysis of two diffuse radio sources, MKTJ0355-4237 and MKTJ0355-4230, to assess their nature and investigate their radio spectral and magnetic field properties through radio polarimetric analysis. We use deep MeerKAT L-band (1.28 GHz) observations to perform spectral analysis of the diffuse emission and study its polarisation properties via rotation measure synthesis. These are complemented by eROSITA X-ray data and DESI photometric redshift catalogues to characterise the host cluster environments. MKTJ0355-4237 is confirmed as cluster-scale minihalo with extent of $\sim 400$ kpc, while the other diffuse source MKTJ0355-4230 remain uncertain and could be either associated with a radio minihalo or radio tailed galaxy. Both show steep spectra ($\alpha \approx -0.7$ to $-0.8$) that steepen toward the outskirts ($\alpha \lesssim -2.5$), consistent with spatial variations in electron ageing and re-acceleration. Polarised emission is detected in both systems, with fractional polarisation $\sim1\,\%$ in the centres and increasing in the outer regions of MKTJ0355-4237. MKTJ0355-4230 is associated with a previously uncatalogued cluster and shows an X-ray morphology offset from the brightest cluster galaxy, indicative of dynamical activity. MKTJ0355-4237 exhibits a sharply bounded internal radio deficit without a corresponding X-ray counterpart, within current sensitivity limits. The spectral steepening supports turbulent re-acceleration as the origin of the diffuse emission.
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All authors Sam Taziaux, Christopher J. Riseley, Stefan W. Duchesne, Francesca Loi, Alec J. M. Thomson, Aritra Basu, Timothy J. Galvin, Dominik J. Bomans

Astrophysics of Galaxies

Atomic hydrogen in $z=0$ galaxies in the COLIBRE simulations

Kyle A. Oman, Ruby J. Wright, Andrea Gebek et al. (+12 more)

We present an overview of the properties of atomic hydrogen (HI) in galaxies at redshift $z=0$ in the COLIBRE cosmological galaxy formation simulations. COLIBRE directly simulates the multi-phase interstellar medium (ISM) and includes new methods to follow radiative cooling to $\approx 10\,\rm{K}$, non-equilibrium chemistry coupled to dust, and dust formation, growth & destruction. We focus on the $(200\,\rm{cMpc})^3$ volume with resolution elements of $2\times 10^{6}\,\rm{M}_{\odot}$. No HI properties informed the calibration of model parameters and yet we find very good agreement with the observed $M_{\star}$-$M_{\rm{HI}}$ relation, the HI mass and velocity width functions, the HI mass-size relation, and (baryonic) Tully-Fisher relations, albeit with some mismatches at the extremes of the galaxy population. HI surface density profiles are realistic, except at large radii around massive ($M_{\star}\gtrsim 10^{10}\,\rm{M}_{\odot}$) galaxies where we find a population of possibly spurious circumgalactic HI clouds, whose abundances and masses decrease, however, with increasing mass resolution). Using smaller simulations to vary some of the uncertain model parameters, we find that the main scaling relations are at most mildly affected, although this may not extend to detailed HI morphokinematics. Convergence across mass resolution levels a factor of $8$ higher and lower is good: the median HI mass and HI `occupation fraction' as a function of halo mass, and the HI mass function, are remarkably stable, although the highest resolution model overproduces HI sources by a factor of $\approx2$ at $M_{\rm{HI}}\gtrsim 3\times 10^{9}\,\rm{M}_{\odot}$. Upturns in the low-mass and low-velocity slopes of the HI mass and velocity width functions with potentially subtle observational signatures are predicted.
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All authors Kyle A. Oman, Ruby J. Wright, Andrea Gebek, Diego Dado, Katherine E. Harborne, Evgenii Chaikin, Carlos S. Frenk, Filip Huško, Claudia D. P. Lagos, Aaron D. Ludlow, Sylvia Ploeckinger, Alexander J. Richings, Matthieu Schaller, Joop Schaye, James W. Trayford

Astrophysics of Galaxies

Phase Separation of HI in the Draco Nebula: CNM formation Triggered by Colliding WNM Flows

Yuhi Naruse, Hiroaki Yamamoto, Yamato Matsuzuki et al. (+3 more)

We investigate the thermal phase structures and kinematics of atomic hydrogen (H I) gas in the Draco nebula to clarify how infalling H I evolves toward cold atomic and molecular clouds. Using the DHIGLS H I 21 cm data, we apply the Regularized Optimization for Hyper-Spectral Analysis (ROHSA) algorithm to decompose the emission into spatially coherent Gaussian components, and classify them as warm neutral medium (WNM), lukewarm neutral medium (LNM), and cold neutral medium (CNM). We identify two kinematically distinct WNM components: WNM1 near $-3$ km s$^{-1}$ and WNM2 near $-30$ km s$^{-1}$. The LNM forms a broad velocity bridge between two WNMs, whereas the CNM is concentrated within a narrower intermediate velocity range. CO emission is also confined to this interval and is associated with CNM-rich regions. The H I mass fractions are $\sim 41\%$, $\sim 23\%$, $\sim 17\%$, and $\sim 19\%$ for WNM1, WNM2, LNM, and CNM, respectively, with the LNM and CNM together accounting for $\sim 36\%$ of the total H I mass. No comparably independent WNM component is recovered at intermediate velocities, although a weak broad component may remain unresolved. The observed phase structures are consistent with a dynamically compressed multiphase interaction layer in which compression increases the gas density, shortens the radiative cooling time, and drives the evolution from WNM through thermally unstable gas toward the CNM. The present interaction may both create new CNM, and further compress or grow pre-existing dense structures. Our results provide the missing link between previous evidence for dynamical interaction and molecular cloud formation in Draco, and identify CNM formation as a key step in transforming gas accreting toward the Galactic disk into cold atomic and molecular clouds.
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All authors Yuhi Naruse, Hiroaki Yamamoto, Yamato Matsuzuki, Rin Yamada, Atsushi Nishimura, Toshikazu Onishi

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

IC 1297: The Most Distant Known X-ray Planetary Nebula and One of the Most Luminous

H. Yuan, Q. A. Parker and M. A. Guerrero

We present the first targeted Einstein Probe (EP) X-ray observations of any planetary nebula (PN). Using the onboard Follow-up X-ray Telescope (FXT), we detect X-ray emission within the central region of IC 1297. The spectral analysis yields a plasma temperature of $kT = 0.086^{+0.054}_{-0.058}$ keV ($T\sim1.0 \times 10^{6}$ K), characteristic of shocked wind bubbles in PNe, whereas there is no evidence that its Wolf-Rayet central star emits X-rays. The absorption-corrected X-ray luminosity in the 0.3–2.0 keV energy band is $L_{\mathrm{X}} = 2.8 \times 10^{32}$ erg s$^{-1}$, also consistent with a hot bubble. At an adopted distance of $\sim3.8$ kpc, IC 1297 is the most distant X-ray emitting PN found to date, opening up a new observational window on hot-bubble formation and evolution. It is also among the most luminous known X-ray-emitting PNe. Our results demonstrate the capability of the EP FXT for detecting and characterizing faint, extended X-ray sources in the soft X-ray band for distant PNe, extending the known spectral properties of detectable X-ray emitting PNe. We also compiled the X-ray properties of all 41 known Galactic XPNe, finding a clear correlation between distance and X-ray luminosity that reflects an observational bias toward detecting the brightest sources at large distances. The compilation also shows a separation in X-ray luminosity between hot bubbles powered by H-rich and [WR]-type central stars, with the latter reaching luminosities up to an order of magnitude higher. The ten most luminous XPNe all host [WR]/PG 1159 central stars.
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Astrophysics of Galaxies

Non-equilibrium chemistry and radiation hydrodynamics in metal-poor and metal-rich interstellar gas

Shyam H. Menon, Piyush Sharda, Blakesley Burkhart et al. (+1 more)

We present a flexible implementation of non-equilibrium chemical networks with the $\texttt{KROME}$ framework, coupled to a nonlocal variable Eddington tensor-closed radiation transport scheme ($\texttt{VETTAM}$). Our fiducial network is designed to explicitly capture the formation pathways of important molecular species such as CO, OH, and $\rm H_2O$, intermediaries like $\rm H_3^+$, and the destruction of these species through photon and cosmic-ray dissociation. We validate our scheme through benchmark tests, and demonstrate its success in 1D and 3D problems covering a broad range of metallicities ($0 \leq Z \lesssim \rm Z_{\odot}$) and densities ($n \lesssim 10^{17} \, \rm cm^{-3}$). We confirm earlier works that suggest that OH and $\rm H_2O$ are the key molecular species in dense gas ($n \gtrsim 10^{5} \, \rm cm^{-3}$) for $Z\lesssim 0.01 \rm Z_{\odot}$, dominate the cooling at these densities, and demonstrate that our scheme can reproduce their abundances with similar accuracy as dedicated static photo-dissociation region (PDR) codes. We also find that the dominant fine-structure coolant in dense ($n \gtrsim 10^3 \, \, \rm cm^{-3}$) PDRs transitions from CI to CII to OI at increasingly lower $Z$. Finally, we find that in turbulent media, rapid mixing at PDR interfaces renders the chemical species out of equilibrium, and show that this could potentially alleviate the long-standing problem of (static) PDR models producing excess CI in the diffuse ISM over UV absorption-line measurements. We conclude by presenting and comparing with alternative implementations of reduced but faster chemical networks in our scheme, discussing the problem-dependent performance-accuracy tradeoffs and future prospects.
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All authors Shyam H. Menon, Piyush Sharda, Blakesley Burkhart, Tommaso Grassi

Astrophysics of Galaxies

Mergers may not be the main channel for galaxy stellar mass growth at redshift $z\gtrsim5$: Predictions from cosmological hierarchical models and simulations

Hao Fu, Mohammadreza Ayromlou, Francesco Shankar et al. (+13 more)

Mergers are a crucial channel of galaxy growth, but their role relative to star formation remains uncertain at high redshift. Here we investigate merger rates and merger-driven stellar mass assembly for galaxies with stellar mass $M_\star \gtrsim 10^8 \, {\rm M_{\odot}}$ at $z\simeq 5-11$, by combining complementary theoretical approaches within $\Lambda$CDM. These include the DECODE semi-empirical model, the TNG100 and EAGLE hydrodynamical simulations, and the L-Galaxies semi-analytical model, together with the Millennium and TNG100-Dark simulations used to examine dark matter subhalo statistics and merger timescales. This compares models with different treatments of baryonic physics and galaxy-halo connections. We find that dark matter-only simulations predict merger timescales $\sim 30\%$ longer than those inferred from cosmological simulations including baryons. Galaxy major merger ($M_{\rm \star,sat} / M_{\rm \star,cen} > 0.25$) rates are high at cosmic dawn and increase towards earlier epochs, reaching $\sim 1/{\rm Gyr}$ at $z\sim 5$ and peaking at $\sim 3/{\rm Gyr}$ at $z\sim 8$. Despite these high rates, mergers contribute only $\lesssim 10\%$ of the total cosmic stellar mass density evolution. The ex-situ stellar mass fraction ranges from a few percent to $\sim 20\%$ for all galaxies at $z\gtrsim 5$, across different models and simulations. Their broad agreement implies that stellar mass assembly at cosmic dawn is dominated by in-situ star formation rather than mergers. These findings suggest that the high pair fractions identified by JWST may not directly trace efficient ex-situ stellar mass growth, highlighting the need for physically motivated merger timescales to interpret galaxy assembly in the early Universe.
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All authors Hao Fu, Mohammadreza Ayromlou, Francesco Shankar, Lars Hernquist, Andrea Lapi, Daniel Roberts, Feng Yuan, Maulik Bhatt, Evgenii Chaikin, Simona Gallerani, Luca Graziani, Antonio La Marca, George Mountrichas, Yingjie Peng, Haocheng Wang, Kai Wang

Astrophysics of Galaxies

A radio counterpart of the local little-red-dot J092359+415736

Tao An, Ruqiu Lin and Ailing Wang

Little red dots (LRDs) are compact red sources at z>~4. Broad lines suggest accreting black holes, yet radio and X-ray measurements are usually weak. Local LRDs allow multi-frequency, multi-epoch radio studies that are inaccessible at high redshift. We search archival radio images for a counterpart to the local LRD J092359+415736 at z~0.323, quantify its long-term radio variability, and identify the plausible origin of the radio emission. Flux densities at the optical position are measured in FIRST, LoTSS, RACS, VAST, and VLASS products spanning 0.144-3.0 GHz and 1994-2024. A compact 144 MHz counterpart is detected at 42sigma in LoTSS, coincident with the Gaia position, and is recovered in FIRST, RACS, VAST, and VLASS. LoTSS and ASKAP give a spectral index alpha ~ -0.30 +/- 0.11. The source varies on multiple timescales: FIRST at 1.4 GHz (1994) is a factor of ~2.6 below ASKAP (2021-2024) and below the extrapolated LoTSS-ASKAP spectrum, indicating long-term brightening over 26 yr; the 3 GHz flux density rises by 2.3sigma between VLASS epochs 2.2 and 3.2. A star-formation-only origin would require ~200 Msun/yr, against an unobscured H-alpha upper limit of 3.3 Msun/yr, implying an extreme obscured starburst. Ordinary radio supernovae and tidal disruption events are strongly disfavoured by the luminosity and 30-yr recovery, while refractive scintillation would itself require an ultracompact nuclear emitter. The persistent radio counterpart is best explained by accretion onto the central black hole. Among the three radio-detected local LRDs, this source is intermediate in luminosity and the only one with reported multi-year variability, adding a temporal dimension to the radio diversity of the class.
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Astrophysics of Galaxies

Sulphur-bearing molecule survey towards prestellar and starless cores in the Perseus molecular cloud

J. Ferrer Asensio, S. Scibelli, A. Pokorny-Yadav et al. (+7 more)

Sulphur is drastically depleted from the gas phase in dense starless and prestellar cores, creating the long-standing "missing sulphur problem". Observations of sulphur-bearing molecules are crucial to understanding sulphur chemistry, core-environment relationships, and the physical evolution of star-forming regions. We present a survey of four sulphur-bearing molecules, HCS+, OCS, H2CS, and SO, towards 15 starless and prestellar cores in the Perseus molecular cloud using the Yebes 40m telescope. The HCS+ 1-0, OCS 3-2 and 4-3, H2CS 1_{0,1}-0_{0,0}, and SO 3_2-2_2 transitions were observed, fitted with Gaussian profiles, and column densities were calculated assuming local thermodynamic equilibrium (LTE). We also compare these with observations of CS, CCS, and CCCS from a previous study. HCS+, OCS, H2CS, and SO are detected in 100%, 93%, 100%, and 73% of the sample, respectively. Derived column densities are (2.2-17.0)x10^11 cm^-2 for HCS+, (1.9-25.0)x10^12 cm^-2 for OCS, (1.0-15.0)x10^12 cm^-2 for H2CS, and (0.3-17.0)x10^13 cm^-2 for SO, spanning over an order of magnitude. HCS+ and SO abundances strongly correlate (inversely and directly, respectively) with core volume density, reinforcing their early- and late-type status. Correlations indicate a differentiation between carbon and oxygen chemistry for sulphur-bearing molecules, with CS showing the strongest correlations as expected. Cores in protostellar outflow paths do not show consistently higher abundances. The chemical age (SO/CS) correlates with physical age (volume density), except for Per752, an outlier likely linked to an enhanced cosmic ray ionization rate. These results provide a robust observational baseline constraining chemical models of sulphur chemistry in early star formation.
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All authors J. Ferrer Asensio, S. Scibelli, A. Pokorny-Yadav, L. Steffes, B. Kulterer, Y. Shirley, A. Megías, I. Jiménez-Serra, A. Fuente, G. Esplugues

Monday 12 October

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

Henrietta Leavitt's classical Cepheid relation

Daniel Majaess

The Leavitt & Pickering (1912) mean period-magnitude relation for SMC Cepheids exhibits correlated residuals relative to modern Gaia $B_G$ and Johnson $V$ photometry ($r_{\delta V/\delta L12}\approx0.76$). Therefore dispersion inherent to Leavitt's photographic photometry relation is not solely random scatter ($\sigma_{L12,B_G,V}=0.22\pm0.03,0.25\pm0.04,0.20\pm0^{m}.03$), and is potentially consistent with the partial encoding of combined effects from the elongated SMC, classical Cepheid instability strip, differential reddening, etc. OGLE data indicate that $\gtrsim870$ SMC variables identified by Leavitt (1908, Table 2) are classical Cepheids ($\gtrsim 90$ %), and the preliminary unphased Table 2 photometry likewise features correlated residuals relative to contemporary observations ($r_{\delta B_G/\delta L08-T2}\approx0.54$). Table 6 data in Leavitt (1908, $n=16$) define a highly linear Leavitt law over an extensive baseline ($r\approx-0.98$), but constitute a smaller sample than the later 1912 work ($n=25$).
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Astrophysics of Galaxies

Intermittency in the Multiphase ISM — II. Non-Gaussian Dust Polarization and Foreground Variance

Yue Hu

Interstellar turbulence produces non-Gaussian polarized Galactic dust emission whose higher-order statistics depend on thermal phase and turbulent forcing. We synthesize optically thin dust polarization from three thermally multiphase diffuse interstellar medium (ISM) simulations with compressive, mixed, and solenoidal forcing. We characterize the resulting non-Gaussian structure in the warm, unstable, and cold phases using $E$- and $B$-mode spectra, one-point distributions, scale-dependent increments, and Minkowski functionals. Both $E$ and $B$ modes are intermittent. Warm-phase emission remains closest to Gaussian, whereas cold gas shows flatter intermediate-scale spectra, broader non-Gaussian tails, and the strongest departures from Gaussian morphology. Compressive forcing generally produces the strongest projected intermittency, particularly in the cold phase and total emission, while mixed and solenoidal forcing show weaker signatures. These higher-order structures also enhance spatial fluctuations in polarized dust power: Gaussian fields matched to the same two-point covariance underestimate the region-to-region scatter by factors of up to $\sim2.6$. Our results show that thermal phase and turbulent forcing regulate not only the mean polarized dust spectrum but also the field-to-field distribution of foreground power, with implications for modeling Galactic foreground in CMB polarization measurements.
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Astrophysics of Galaxies

Untangling Similarities and Differences in Star Formation Histories Across Cosmological Simulations

Alicia M. Savelli, Matthew A. Kustec, Joshua S. Speagle et al. (+5 more)

How galaxies assemble depends on processes ranging from small-scale baryonic physics to large-scale cosmological assembly, which are difficult to disentangle with observations alone. Using $\sim$63,000 simulated galaxies from seven cosmological simulations spanning hydrodynamical, semi-analytic, and semi-empirical models, we explore how specific star formation histories (sSFHs) vary across modelling assumptions. Using non-linear dimensionality reduction (UMAP), we find that sSFH shape variation organizes along a few smooth axes in a 2D embedding, broadly corresponding to (1) peak timing, (2) peak sharpness, and (3) subsequent quenching rate. We identify sSFH shapes that many simulations share ("common"), well described to first order by dark matter halo assembly, and a few tied to individual simulations ("unique"), which likely reflect subgrid and parametrization choices such as merger-triggered burst prescriptions. A notable exception is a common population of rapidly quenched galaxies found across most simulations, likely driven by e.g., active galactic nucleus (AGN) feedback, that halo assembly alone cannot reproduce. The origin of the most distinctive unique shape, an Illustris-dominated history with an early peak and slow decline, remains unclear, but we test the effects of short-term variability. With a multi-objective auto-encoder neural network, we recover the simulation that a given sSFH is drawn from with $\sim$95% out-of-sample accuracy; ablation tests indicate this information is embedded in long-timescale sSFH morphology rather than short-term variability. These results provide avenues for theoretical and observational follow-up connecting star formation histories to subgrid physical models.
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All authors Alicia M. Savelli, Matthew A. Kustec, Joshua S. Speagle, Kartheik G. Iyer, Eshal Ahmed, Zehao Peng, Norman Murray, Cissy Kuang

Astrophysics of Galaxies

Intermittency in the Multiphase ISM — I. Extreme Density, Velocity, and Magnetic Fluctuations

Yue Hu

Intermittency is a fundamental property of astrophysical turbulence because it concentrates strong gradients, dissipation, and transport into rare, localized structures. In the multiphase interstellar medium (ISM), turbulent driving is especially important because the balance between compressive and solenoidal motions can regulate how extreme fluctuations are distributed among thermal phases. Yet conventional increment statistics quantify intermittency without identifying the structures that host it. We analyze three matched ideal-MHD simulations of a thermally multiphase neutral medium that differ only in the compressive fraction of the driving. Density, velocity, and magnetic-field increments are non-Gaussian in every thermal phase. Increasing compressive driving redistributes density and magnetic fluctuations preferentially into the cold gas rather than uniformly enhancing them across phases. We identify the structures associated with extreme increments using local, scale-matched diagnostics of compression, thermal gradients, vorticity, strain, magnetic curl, and magnetic tension. Extreme magnetic increments preferentially occur where magnetic curl and magnetic tension are simultaneously enhanced, more strongly than extreme velocity increments are associated with their kinematic hosts. Extreme velocity increments show comparable enrichment in vorticity and strain, whereas extreme density increments preferentially trace converging flows and thermal gradients only in the unstable medium. These associations weaken beyond a phase-dependent coherence scale. Our results show that turbulent driving controls how intermittency is partitioned among thermal phases, while distinct physical structures host extreme density, velocity, and magnetic fluctuations.
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Astrophysics of Galaxies

Physical characteristics of the Galaxy defining the oscillation period of librating orbits near the OLR of the bar

A. M. Melnik and E. N. Podzolkova

We studied librating orbits of stars near the Outer Lindblad Resonance (OLR) of the bar using the angle-action variables of Hamiltonian dynamics. The librating orbits change the direction of their elongation relative to the major axis of the bar in a limited range of angles. To calculate orbits, we used the model of the Galaxy with an analytical bar which reproduces well the distributions of the observed stellar velocities along the Galactocentric distance R derived from the Gaia DR3 data. We compared the values of the orbital oscillation period of a typical star obtained from the theory and with the use of numerical simulation. Both values were found to be in good agreement and are equal to 2.0 Gyr. It was shown that the change in the average orbital radius, <R>, of a star, calculated over the time interval of one radial oscillation, is regulated by the change in the direction of orbital elongation. As the orbit is tilted relative to the minor axis of the bar in the sense of Galactic rotation, the angular momentum of the star, L, decreases, on average, causing a decrease in <R>. As the orbit is tilted in the opposite direction, <L> and <R> increase. We derived a general formula for the oscillation frequency, omega, of orbits captured by libration near the OLR of the bar. It turned out that the ratio of the frequency of orbit oscillations to the epicyclic frequency, omega/kappa, is determined by the parameters q_R and <p>, where the factor q_R is the ratio of the amplitude of the radial force generated by the bar to the average radial force produced by the entire galaxy at the distance of the OLR, and the parameter <p> characterizes the average elongation of orbits captured by libration near the OLR.
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Astrophysics of Galaxies · Cross-listed from astro-ph.SR

An upper limit on Galactic OB+black hole binaries from SDSS-V

J. Müller-Horn, H.-W. Rix, S. Shahaf et al. (+14 more)

Binaries composed of a luminous OB star and a black hole (BH) are a key evolutionary link between massive stellar binaries and merging compact-object binaries, but only a handful are known and their occurrence fraction remains poorly constrained. We use multi-epoch spectroscopy from the SDSS-V Milky Way Mapper to place a first rigorous empirical upper limit on the fraction of Galactic massive ($\geq 10\,\mathrm{M}_\odot$) OB stars with a close BH companion, $f_\mathrm{BH}$. Radial-velocity (RV) variability alone cannot distinguish BH companions from the far more numerous luminous binaries. We therefore combine the SDSS-V RV variability measurements of 3130 massive OB stars with high-resolution follow-up and literature information to identify luminous companions among the RV-variable subset. Forward-modelling the detectability of OB+BH systems using BH masses and orbital parameters from binary-evolution models, we find $f_\mathrm{BH} \lesssim 3\%$ at 95% credibility. This empirical upper limit approaches, but does not exclude, theoretical predictions for the OB+BH fraction. The constraint is primarily limited by the number of RV-variable systems that can be decisively classified, highlighting the importance of complete, high-quality follow-up for future searches.
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All authors J. Müller-Horn, H.-W. Rix, S. Shahaf, B. Pennell, E. Zari, M.C. Ramírez-Tannus, A. Farah, R. Essick, J.I. Villaseñor, M.R. Blanton, J.G. Fernández-Trincado, J.A. Kollmeier, C. Lam, K. Maltsev, A. Roman-Lopes, D.P. Schneider, A. Tkachenko

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

Scaling Up: A Global Optical/X-ray Correlation For Reprocessing Across Black Hole Masses

Changhyun Cho, David M. Russell, Aaryan Sharma et al. (+9 more)

This study extends the optical/X-ray correlation from black hole low-mass X-ray binaries (XRBs) to active galactic nuclei (AGN), bridging scales from stellar-mass to supermassive black holes (SMBHs). In XRBs, optical emission predominantly originates from the thermal reprocessing of high-energy photons on the surface of the geometrically thin, optically thick accretion disk. The reprocessed optical luminosity follows a power-law relation of the form $L_{V} \propto L_{X}^{\beta} a$, with $\beta \sim 0.5$, where $L_X$ is the X-ray luminosity and the orbital separation $a$ serves as a proxy for the disk size. To test the universality of this relationship across all mass scales, we analyzed quasi-simultaneous X-ray and optical flux data from a sample of XRBs and AGN that have estimates of the radius of the optically emitting disk. To bridge the structural differences between these populations, we utilized the characteristic optical/X-ray time lag derived from reverberation mapping as a physical proxy for the reprocessing radius. Our analysis reveals a tight, global correlation across all black hole masses, described by $\log L_V = 0.48\log L_X + 0.96\log a_R + 6.5$ with a scatter of $\sim 0.20$ dex, where $a_R$ is the reprocessing radius derived from the lag. Incorporating a geometric correction for the disk inclination angle ($\cos i$) slightly reduces this scatter to $0.18$ dex. These results suggest that X-ray reprocessing is scale-invariant across accretion disks, from stellar-mass black holes to SMBHs. This scaling relation provides new constraints for models of X-ray emission regions in accreting black holes.
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All authors Changhyun Cho, David M. Russell, Aaryan Sharma, Payaswini Saikia, Maria Cristina Baglio, Kevin Alabarta, Sandeep K. Rout, Yi-Jung Yang, Eleonora Caruso, Mokhine Motsoaledi, Meriana Allah, Ian M. McHardy

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

From Giant Envelopes to Rapidly Contracting Cores in Rotating Population III Stars from $500$ to $1000 \, M_\odot$

Devesh Nandal, John Chisholm, Daniel J. Whalen et al. (+4 more)

Population III (Pop III) stars link the chemical enrichment of the early Universe to the formation of the first massive black holes, yet their evolution remains poorly understood at extreme masses. Using GENEC, we evolve rotating zero metallicity models from $500$ to $1000\,M_\odot$ at $v/v_{\rm crit}=0.1$ through core Si burning, and a $1000\,M_\odot$, $v/v_{\rm crit}=0.4$ model evolved through He exhaustion. In the fiducial $1000\,M_\odot$ model, convection and rotational transport carry freshly synthesized C and O into H burning layers, producing $62.1\,M_\odot$ of primary N by He exhaustion. Surface mass loss removes $20.2\,M_\odot$, including $1.8\times10^{-3}\,M_\odot$ of N, with $\log(\mathrm{N}/\mathrm{O})=0.68$, $\log(\mathrm{N}/\mathrm{C})=1.48$, and $\log(\mathrm{C}/\mathrm{O})=-0.80$. By the final hydrostatic model, the inner $100\,M_\odot$ is confined within $0.088\,R_\odot$ while the photosphere remains several thousand solar radii away. As C, Ne, O, and Si burning accelerate, chemical mixing freezes out and advanced products remain buried beneath the envelope. At core Si exhaustion, the central angular velocity reaches $4\times10^{-3}\,{\rm s^{-1}}$ while the surface rotates at $5.25\times10^{-8}\,{\rm s^{-1}}$, a contrast of $7.6\times10^4$. Contraction drives this spin up, while inner specific angular momentum changes by less than $1\%$. The maximum $j_{\rm eq}/j_{\rm ISCO}$ is $0.313$, limiting disk formation in our inside out estimate. These models show that Pop~III stars can produce strong primary N signatures and rapidly rotating black hole progenitors while their envelopes determine which products enrich the early Universe.
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All authors Devesh Nandal, John Chisholm, Daniel J. Whalen, Andreas A.C. Sander, Volker Bromm, Peixin Zhu, Lisa J. Kewley

Astrophysics of Galaxies

Magnetic field evolution in feedback-dominated galaxies

Yue Samuel Lu, Dušan Kereš, Philip F. Hopkins et al. (+1 more)

Over the last decade, magnetic fields (B-fields) have become a common ingredient in galaxy formation simulations. Although seemingly unimportant in matching observational constraints such as the $M_*-M_{\rm halo}$ relations, the B-field influences the circumgalactic medium (CGM) gas and determines cosmic ray (CR) propagation, making it an indispensable non-thermal component. Nevertheless, the intricate physics of B-fields, particularly how they evolve to the observed $\mu$G-level field, remains largely elusive. In this work, we systematically address the evolution of B-fields over cosmic time using the FIRE-2 (Feedback In Realistic Environments) magnetohydrodynamics (MHD) simulations. We present results for both Milky Way (MW)-mass and dwarf galaxies, with and without CRs. We find that CRs have little impact on B-field properties, while the halo mass controls the saturated B-field strength at $z\sim 0$. However, all runs reach a halo-independent magnetic-to-turbulent ratio of $f_{\rm B}\sim 1-10\%$, though the methods used to measure turbulence could affect this value. We identify a three-stage evolutionary course for the B-field in tandem with galaxy formation: i. expansion, ii. amplification, and iii. saturation. The feature is universal, though the timings depend on the initial location and star formation history of the gas. Flux-freezing is the predominant driver for the first and last stages, exhibiting power relations $B\sim \rho^{2/3}$ and $\rho^{1/2}$, although the latter could also be explained by dynamical and energetic equilibria. The intermediate amplification stage, potentially driven by “dynamos”, is fuelled by structure formation, feedback, and gas turbulence. We conjecture a numerically triggered, turbulence-driven amplification process to explain this phenomenon.
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All authors Yue Samuel Lu, Dušan Kereš, Philip F. Hopkins, Sam B. Ponnada

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

MRI Turbulence versus $\alpha$-Viscosity in Circumbinary Disks: Implications for Gravitational-Wave Dephasing and Accretion Variability

Mudit Garg and Yan-Fei Jiang

Our understanding of gas torques on massive black hole binaries (MBHBs) relies on hydrodynamical (HD) simulations of circumbinary disks (CBDs) in which an $\alpha$-viscosity models angular momentum transport. However, CBDs around MBHBs near merger are hot, magnetized plasmas where transport is driven by magnetohydrodynamical (MHD) turbulence sustained by the magnetorotational instability (MRI). We test how well an $\alpha$-viscosity captures MRI turbulence with 3D global Athena++ simulations of a locally isothermal CBD around an equal-mass, circular MBHB, run in HD and MHD from the same initial torus on identical grids, so that only the transport mechanism differs. Excising the region within twice the binary separation, $r<2~a_{\rm bin}$, allows $1000$ orbits of evolution, several times longer than previous MHD simulations. Both disks deliver the same accretion rate, and the gas beyond $2~a_{\rm bin}$ exerts a positive torque in both, yet the MHD torque is $3.5$ times larger and $3$ times more variable. Near the midplane, transport is similar in the disk body but three times weaker in MHD at the cavity edge, where $2$-$3$ times more mass piles up in a more eccentric cavity, raising the torque. The accretion rate is modulated mainly at twice the binary frequency in HD, but by a persistent lump at the cavity edge and its beat with the binary in MHD. The outer-disk torque therefore implies a contribution to the gas-induced phase shift in the gravitational-wave signal of LISA binaries $3.5$ times larger than in $\alpha$-disk models, and a different variability signature for LSST and Roman.
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Astrophysics of Galaxies · Cross-listed from astro-ph.CO

Interpreting the stacked kinetic SZ signal II: the degeneracy between satellite galaxies and baryonic feedback

Lurdes Ondaro-Mallea, Boryana Hadzhiyska and Raul E. Angulo

The kinetic Sunyaev-Zel'dovich (kSZ) signal stacked around a galaxy sample traces the gas around halos and is a powerful probe of baryonic feedback. Its interpretation, however, depends on the satellite galaxies in the sample. Using the FLAMINGO hydrodynamical simulations and DESI-like samples of luminous red galaxies (LRGs), bright galaxies survey (BGS), and emission-line galaxies (ELGs), we show that satellites and feedback have similar effects: both suppress the small-scale signal. This degeneracy arises because stacking on satellites, which are offset from the centre of their host haloes, mimics the extended gas distribution produced by feedback. Although satellites make up only 20-30% of each sample, they account for 50-80% of the signal because they occupy more massive halos than centrals; thus their imprint on the stacked profiles can be as large as that of feedback. At the precision of current DESI$\times$ACT data, neglecting satellites in the modelling biases the inferred gas fractions low, by up to a factor of two, and overestimates the feedback strength, particularly for the LRG and BGS samples. Remaining agnostic about the satellite population avoids this bias but reduces the constraining power, so robust constraints would require knowing the satellite fraction to better than 10%, for instance from lensing and clustering data of the same galaxy samples. Finally, a further contribution from satellites will become statistically significant with upcoming surveys: satellites trace the anisotropic gas distribution around their host haloes, an effect that contributes 10% of the signal, and will likely require simulation-based models to capture.
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Astrophysics of Galaxies · Cross-listed from astro-ph.SR

The nearby Type II supernova 2024ggi beyond 600 days: circumstellar interaction and dust formation

L. Ferrari, G. Folatelli, C. P. Gutiérrez et al. (+16 more)

The Type II SN 2024ggi is one of the nearest core-collapse SNe to have exploded in recent decades. Its proximity has enabled extensive multiwavelength monitoring from early times through the nebular phase. Signatures of late-time interaction between the SN ejecta and hydrogen-rich circumstellar material (CSM) have recently been reported. Here we extend its study using late-time optical photometry and spectroscopy from 570 to 820 d after explosion. We investigate the emergence and evolution of late-time ejecta-CSM interaction and constrain the geometry of the interaction region and the properties of newly formed dust. Comparisons with other interacting SNe II and with synthetic spectra are presented. We model the H$\alpha$ profile with the Monte Carlo radiative-transfer code Damocles, including both gas and dust components. Spectroscopic signatures of interaction precede the photometric flattening. The spectra evolve from ejecta-dominated to interaction-dominated as H$\alpha$ develops a broad, boxy profile. The optical light curves subsequently flatten relative to the $^{56}$Co decay rate at approximately 650-670 d. The emission lines show a systematic blue-to-red asymmetry that requires a dust component newly formed within the ejecta. The inferred dust mass formed in the ejecta is $10^{-6}-10^{-5}$ M$_\odot$ if the grains are amorphous carbon or a carbon-silicate mixture, but can reach up to $10^{-3}$ M$_\odot$ for pure silicates.
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All authors L. Ferrari, G. Folatelli, C. P. Gutiérrez, A. Méndez, C. Ashall, K. Medler, K. Ertini, H. Kuncarayakti, N. Morrell, M. Stritzinger, W. Hoogendam, E. Hueichapán, R. Cartier, J. P. Anderson, M. Bersten, L. Galbany, J. L. Prieto, C. Cárdenas Uribe, S. Vazhayil

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

Extinction by non-spherical particles with the Nanoparticle Transition Matrix Code: perspectives for interstellar medium and exoplanetary atmospheres

G. La Mura, G. Mulas, M. A. Iatì et al. (+4 more)

The Transition Matrix formalism (T-matrix) offers an optimal solution to the problem of radiation scattering and absorption by particles characterized by a high degree of chemical and structural complexity. However, its application to particle models composed by large numbers of constituents has been classically limited by the substantial computational burden of the method. As a consequence, the investigation of light scattering and absorption processes, in cases where particle asymmetry and non-homogeneity play an important role, typically need to rely on simplifying assumptions which affect the correct interpretation of transmission spectra and extinction curves. This problem has a huge impact on many fields of scientific application. In particular, it has a critical role in astrophysics, because the ability to model highly non homogeneous particles is a fundamental requirement to understand the role of extinction in different phases of the interstellar medium (ISM), as well as to probe the physics of light transmission in planetary atmospheres within the Solar System and beyond. In this work we describe the application of a new implementation of the T-matrix formalism, based on the framework originally developed by Borghese, Denti & Saija and named Nano-particle Transition Matrix code, which leverages the power of modern hardware architectures to reduce the computational costs related to the solution of relevant particle models for the investigation of dust in the ISM and of hot-Jupyter class planets atmospheric aerosols. This new implementation of the T-matrix formalism can handle calculations of increasing complexity with a direct impact in the interpretation of the transmission spectra of transiting exoplanets produced by the James Webb Space Telescope (JWST) and of those expected from the Atmospheric Remote-sensing Infrared Exoplanet Large survey (ARIEL).
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All authors G. La Mura, G. Mulas, M. A. Iatì, C. Cecchi-Pestellini, G. Aresu, S. Rezaei, R. Saija

Astrophysics of Galaxies

R(V) parameter of the dust extinction curve: mapping based on hot stars and connections to diffuse interstellar bands

R. Lallement, J.L. Vergely and N.L.J. Cox

Favored carriers of the Diffuse Interstellar Bands (DIBs) are carbonaceous molecules whose constituents have been presumably expelled by dying stars along with those of dust grains. The parallel evolution of DIB carriers and grains and their potential interplay are unknown. We assembled published R(V) measurements of 505 hot stars. We inverted a catalog of extinction data based on Gaia XP spectra and NIR photometry, and used the resulting new 3D extinction map to locate the opaque areas responsible for R(V) for each star. Using archived spectra, we measured their 5780, 5797 and 8620 A DIBs. In parallel, we compared local and line-of-sight (LOS) R(V)s from recent 3D maps with local and LOS Gaia DIB strengths from our recent map. Results: R(V)s from hot stars reveal variations on large spatial scales, confirming with independent data the published 3D pattern. Gaia DIB strength maps show large spatial scale variations similar to those of R(V) maps, with higher abundance of DIB carriers corresponding to higher R(V). LOS Gaia DIB strengths and R(V)s from 3D maps also correlate positively in the R(V) range 2.3-3.4, but there is no connection for higher R(V), likely due to the disappearance of DIB carriers in dense clouds. Despite averaging effects along the LOS to hot stars, we find differences in R(V)-DIB relationships among the three DIBs, with an evolution from negative to positive correlation from the zeta- to the sigma-type DIBs. This can be understood in the frame of the bimodal evolution of R(V) with the extinction, with the zeta (resp. sigma) DIB carrier disappearance in the decreasing (resp. increasing) phase of R(V). Various combinations of DIB strengths and DIB ratios may allow to define the range of R(V), but the relationship between DIBs and R(V) also appears to depend on the wavelength range used to determine R(V).
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Astrophysics of Galaxies · Cross-listed from astro-ph.CO

The Cosmic Radio Dipole and Observer Effects in SKA all-sky surveys

D. Bertacca, L. Böhme, B. Bottazzi Baldi et al. (+13 more)

The Square Kilometre Array (SKA) will observe our Universe on the largest scales and so enable the study of fundamental assumptions in cosmology, such as cosmic homogeneity and isotropy. Observations over recent years have reaffirmed an unexpected challenge to the Cosmological Principle first seen in measurements of the cosmic radio dipole. This dipole anisotropy is thought to be caused by our local observer motion, however, it is observed to be about three times larger than predicted, with significances exceeding 5$\sigma$. The SKA is in a unique position to shed light on this anomaly by measuring this and other effects related to our observer motion. To quantify this, we forecast the capability of large-angle HI and continuum surveys of the SKA to constrain the kinematic matter dipole in galaxy number counts, the modulation of the matter power spectrum by a kinematic dipole, and kinematic spectral distortions of diffuse radio emission.
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All authors D. Bertacca, L. Böhme, B. Bottazzi Baldi, C. Burigana, M. Y. Elkhashab, C. L. Hale, S. von Hausegger, H. R. Klöckner, M. Land-Strykowski, G. F. Lewis, V. Mittal, O. T. Oayda, D. J. Schwarz, P. Tiwari, T. Trombetti, J. D. Wagenveld

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

Indirect Dark Matter Detection in the Multi-Messenger Era: Experiments, Systematics, Anomalies, and Prospects for Discovery

Muad Ghaith and Khaled Obaideen

Indirect searches for dark matter (DM) span gamma rays, charged cosmic rays, neutrinos, X-rays, radio emission, the cosmic microwave background (CMB), and the 21~cm signal, but reported constraints and anomalies vary in evidential strength. This critical review synthesizes peer-reviewed literature from January 2000 through October 2026 using a structured search strategy. We assess observations through a framework linking particle interactions and halo source terms to propagation or cosmological energy deposition, instrumental response, background modeling, and statistical inference. Fermi-LAT observations of dwarf spheroidal galaxies provide robust GeV-scale benchmarks for DM annihilation, whereas Galactic-center searches offer higher expected signals but depend more on foregrounds and halo profiles. Charged-cosmic-ray measurements are precise but limited by propagation and source uncertainties, while neutrino searches offer complementary sensitivity through solar capture, directional and flavor information, and high-mass annihilation or decay. Several widely discussed signals, including the 3.5~keV line, 511~keV emission, the Galactic-center GeV excess, charged-particle features, cluster radio excesses, and candidate gamma-ray lines remain inconclusive because of limited independent confirmation, uncertain target scaling, spectral degeneracies, or background-modeling limitations. Cosmological observations provide complementary constraints from CMB energy-injection limits and 21~cm measurements of the intergalactic medium. Artificial intelligence increasingly supports reconstruction and inference but requires rigorous calibration and domain-shift validation. The strongest case for DM discovery would require statistically consistent evidence across independent targets, instruments, or messengers, under common particle-physics parameters, and with well-characterized uncertainties.
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Astrophysics of Galaxies

A Quest for Changing-State AGNs

Kasra Mokhtarpour and Vicki Sarajedini

We use Gaia Data Release 3 (DR3) light curves to identify photometrically selected changing-state active galactic nucleus (CSAGN) candidates. We employ unsupervised deep learning and anomaly detection methods to identify unusual patterns of variability in the light curves of 872,228 AGNs with known variability. We find that 8,504 light curves show anomalous behavior. Among these, 682 sources show evidence for two-state photometric behavior during the Gaia DR3 observing baseline. These 682 CSAGN candidates were selected using an automated statistical pattern recognition approach based on Gaussian mixture models (GMMs) to identify sources whose magnitude distributions are consistent with two preferred brightness levels, substantially reducing the need for human visual inspection in selecting the CSAGN candidates. The candidates tend to have fainter absolute magnitudes and lower redshifts than the non-anomalous Gaia variable AGN sample, suggesting that some may be accreting at lower rates. Our approach builds a large candidate sample with less reliance on human visual selection. Follow-up observations of these sources can help identify what drives changing-state transitions and clarify their connection to accretion-disk physics and supermassive black hole (SMBH) fueling.
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Astrophysics of Galaxies

Unveiling the Hot Interstellar Medium in Nearby Galaxies with eROSITA

Roman Laktionov, Manami Sasaki, Elias Kyritsis et al. (+9 more)

Diffuse X-ray emission in galaxies originates from stellar-feedback-heated gas and unresolved compact sources. We investigate its thermal component and the scaling of X-ray luminosity with star formation rate (SFR), including galaxies with very low SFRs. We analyzed eROSITA/SRG data from the four all-sky surveys (eRASS:4) for a blind, volume-limited sample of 140 galaxies within 25 Mpc from the Updated Nearby Galaxy Catalog (Karachentsev et al. 2013), cross-matched with HECATEv2 (Kyritsis et al. 2026b). Early-type galaxies were analyzed separately, while star-forming galaxies were divided into low-, medium-, and high-specific-SFR (sSFR) subsamples. We modeled the integrated X-ray spectra with thermal plasma and power-law components, stacked spectra for each subsample, and derived total and thermal X-ray luminosities. The stacked spectra show a stronger soft thermal component at high sSFR, whereas low-sSFR and early-type galaxies are increasingly dominated by the harder non-thermal continuum. For star-forming galaxies, the total 0.5-8 keV luminosity follows $\log L_X \sim 39.5 + 0.9\log\mathrm{SFR}$, with an intrinsic scatter of about 0.9 dex. The 0.5-2 keV thermal luminosity follows $\log L_X \sim 38.7 + 1.1\log\mathrm{SFR}$, with an intrinsic scatter of about 0.7 dex. The thermal luminosity remains well correlated with SFR down to $\sim 10^{-5}\,\mathrm{M}_\odot\,\mathrm{yr}^{-1}$ and is consistent with previous relations for star-forming galaxies. By contrast, the flatter and more scattered total X-ray luminosity-SFR relation suggests that unresolved X-ray binaries likely dominate at low SFR, while thermal X-ray emission remains a robust tracer of stellar feedback.
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All authors Roman Laktionov, Manami Sasaki, Elias Kyritsis, Andreas Zezas, Steven Hämmerich, Fiona Knies, Jörn Wilms, Frank Haberl, Martin G. H. Krause, Ashley Coombs, Philipp Weber, Aafia Zainab