Astrophysics of Galaxies · Cross-listed from astro-ph.IM
Lynx2030 Science Analysis Group: Final Report
Lynx2030 Science Analysis Group: Simon R. Bandler, Laura W. Brenneman, Nico Cappelluti et al. (+50 more)
The Lynx2030 Science Analysis Group (SAG) was convened to reassess the scientific goals and technical drivers of the Lynx mission concept amid a rapidly evolving astrophysics landscape. Building on the original Lynx Concept Study, the SAG examined how recent discoveries, emerging facilities, and advances in instrumentation influence the scientific opportunities for a next-generation flagship X-ray observatory. Through focused working groups, the SAG investigated the scientific impact of enhanced capabilities: (i) improved angular resolution, (ii) broader bandpass coverage, (iii) an enhanced microcalorimeter, (iv) new capabilities and observing modes, and (v) larger fields of view. Across a broad range of topics, from the formation of the first black holes and the
evolution of
galaxies to the baryon cycle, compact objects, stellar explosions, multi-messenger astrophysics, and the dynamic high-energy Universe, the SAG finds that the scientific motivation for a Lynx-class observatory remains compelling and, in many areas, has significantly strengthened over the past decade, prominently through JWST's discovery of the "Little Red Dots", likely massive accreting black holes in infant
galaxies whose nature is fundamentally an X-ray question. This report shows that modest extensions beyond the original Lynx design reference mission can unlock transformative science while preserving the observatory's core architecture. Powerful current and future facilities such as Roman, Rubin, JWST, SKA, ngVLA, LISA, and NewAthena highlight the unique role a high-angular-resolution, high-throughput X-ray observatory would play in the multi-wavelength and multi-messenger ecosystem of the 2030s and beyond. The findings of the Lynx2030 SAG confirm Lynx's central
vision: an unprecedented view of the hot and energetic Universe, enabling discoveries that will define high-energy astrophysics in the coming decades.
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All authors Lynx2030 Science Analysis Group: Simon R. Bandler, Laura W. Brenneman, Nico Cappelluti, Daniel Castro, Steven R. Ehlert, W. Peter Maksym, Fabio Pacucci, Scott W. Randall, Grant R. Tremblay, John ZuHone, Steven W. Allen, Antara R. Basu-Zych, Akos Bogdan, Joel N. Bregman, Tamta Burduli, Thomas Connor, Sanskriti Das, Casey DeRoo, Stephen DiKerby, Paul A. Draghis, Martin Elvis, Giuseppina Fabbiano, Ralf K. Heilmann, Jimmy A. Irwin, Amruta Jaodand, Margarita Karovska, Vinay L. Kashyap, Anthony A. Kerr, Caroline Kilbourne, Ralph Kraft, Jiangtao Li, Labani Mallick, Herman L. Marshall, Michael L. McCollough, Anna Ogorzałek, Frederik Paerels, Daniel Patnaude, Paul Plucinsky, David Pooley, Frederick S. Porter, Daniele Rogantini, Roger Romani, Helen R. Russell, Kazuhiro Sakai, Mark Schattenburg, Dan A. Schwartz, Malgorzata Sobolewska, Paolo Soffitta, Alexey Vikhlinin, Daniel R. Wilkins, Scott Wolk, Ka-Wah Wong, Irina Zhuravleva
Astrophysics of Galaxies · Cross-listed from astro-ph.HE
A Self-Sustaining Black Hole Engine Powered by the Tidal Disruptions of Stars
James Guillochon and Avi Loeb
Tidal disruption events (TDEs) strongly prefer host
galaxies undergoing, or recovering from, a burst of
star formation, implying that a rare minority of
galaxy types produces most events. The required per-
galaxy rates, as high as $10^{-2}$ gal$^{-1}$ yr$^{-1}$, are hard to achieve through stellar relaxation alone. Molecular clouds surrounding nuclear clusters help set the relaxation rate, offering a path to higher rates. We show that (post-)starburst
galaxies, whose nearby prototypes contain large molecular gas reservoirs, are likely in a self-sustaining cycle: an enhanced disruption rate compresses the surrounding clouds through momentum injected by the unbound debris, the denser clouds compress the cluster, and the cluster disrupts
stars faster still. The runaway is arrested only when
stars begin to collide. Solving for the steady state, the rate saturates at $1.4\times10^{-2}(M_{\rm h}/10^{6}M_\odot)^{-0.84}$ yr$^{-1}$, two orders of magnitude above the canonical rate at $10^{6}M_\odot$, with a normalization uncertain by a further two orders of magnitude through the stellar collision rate. Three independent requirements — that tidal debris outweigh AGN feedback, that the molecular clouds fit within the disk that holds them, and that the cusp be no denser than observed
nuclei — bound the flattening of the stellar cusp to $0.18 \lesssim f_\ast \lesssim 0.25$. Because no engine can run below a threshold black hole mass, holes seeded beneath it stay dark until
accretion carries them across, switching on after $\sim 1$ Gyr and offering a natural explanation for the late peak recently measured in the TDE delay time distribution. The
nucleus is buried under $A_V \simeq 50$ whatever its geometry, so most such disruptions should be hidden from optical surveys and emerge instead in the infrared.
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Astrophysics of Galaxies · Cross-listed from astro-ph.IM
Exploring the trade-space of distributed aperture telescopes for faint-object spectroscopy
Theodore A. Grosson, Deborah M. Lokhorst and Alan W. McConnachie
Scientific programs targeting the faintest objects push modern
telescopes to increasingly large sizes, high costs and complex designs. Obtaining spectra of low surface brightness
galaxies, for example, requires hours of observations on state-of-the art instruments. Increasing
telescope diameters beyond 40 m raises potentially insurmountable challenges for design and funding. An innovative strategy for combating these costs is to use many small
telescopes in place of a single large aperture. For observations in which high angular resolution is not necessary, this can be equivalent to a large diameter
telescope in terms of sensitivity, while diffraction limited by the individual aperture. Improvements in commercial off-the-shelf (COTS) components have made this concept a possibility, as demonstrated by instruments such as the Dragonfly Telephoto Array, the Huntsman
Telescope, and the Argus Array. In this work, we discuss the merits of "distributed aperture
telescopes" as applied to the use case of spectroscopic observations of ultra-diffuse
galaxies (UDGs). We compare the cost and simulated scientific performance of different configurations of apertures, detectors, and other components for this purpose, finding that an array of half-metre
telescopes can obtain comparable observations to large
telescopes for a fraction of the cost. Finally, we discuss the path to prototyping an array which will enable a spectroscopic survey of UDGs.
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Astrophysics of Galaxies
Radio-dust connection in quasars driven by powerful ionised outflows
V. A. Fawcett, C. M. Harrison, T. Costa et al. (+8 more)
Feedback from dusty
quasars is thought to be a key driver in
galaxy evolution. Multiple studies have reported a link between dust extinction and
radio emission in
quasars, possibly attributed to winds or jets interacting with the interstellar medium. We use optical spectra from the Dark Energy Spectroscopic Instrument (DESI) to test whether ionised outflows could be driving the observed
radio-dust connection and to determine whether dust and/or colour play a role in producing high-velocity ionised outflows in
quasars. Based on a sample of 3418 DESI
quasars at 0.5 < z < 0.9, we constrained the [OIII]$\lambda$5007 kinematics by fitting the spectra with PyQSOFit and comparing the observed trends among the [OIII] outflow velocity and the line-of-sight dust extinction E(B-V), optical-to-mid-infrared (MIR) colour g-W2, and L6$\mu$m/L5100A (a proxy for MIR excess). Utilising
radio data from the LOFAR Two-metre Sky Survey (LoTSS) DR2, we also explored the link between
radio, dust, and outflows. We find that the link between
radio emission and dust obscuration is driven by sources hosting high-velocity ionised outflows. However, we find no significant trend between the [OIII] outflow velocity and E(B-V), which suggests dust extinction alone is not a significant factor in determining whether a
quasar hosts a powerful ionised outflow. On the other hand, we find a clear positive trend between g-W2 and outflow velocity, even after controlling for luminosity. We suggest this is due to a connection between a MIR excess (boosting the W2 band) and outflows, which is supported by a positive trend between L6$\mu$m/L5100A and outflow velocity. Our results point to a scenario in which outflows shock the surrounding dust and gas, heating the dust and boosting both the MIR and
radio emission.
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All authors V. A. Fawcett, C. M. Harrison, T. Costa, D. M. Alexander, C. Andonie, H. Haidar, R. D. Shepherd, C. L. Sargent, M. J. Temple, C. Circosta, D. J. Rosario
Astrophysics of Galaxies · Cross-listed from astro-ph.HE
Decisive evidence for a global cosmic-ray feature in gamma-ray data
Fernando Valenciano, Pedro De la Torre Luque, Daniele Gaggero et al. (+1 more)
We analyze 17 years of Fermi-LAT data to study the diffuse $\gamma$-ray emission along the Galactic plane and its connection to
cosmic-ray (CR) propagation. Accounting for correlated instrumental systematics, we find decisive evidence for a spectral break at $\sim20-30$ GeV, present across the inner Galactic disk, with a preference of $\Delta\chi^2=39.78$ ($4.44 \sigma$ global). The energy and amplitude of this feature are in striking agreement with the spectral feature observed in local CR
nuclei, indicating that it is a global property of the Galactic disk rather than a local phenomenon. The measured slope change, $\Delta\gamma \simeq 0.20$, is consistent with local CR data and with expectations from a transition in the CR
diffusion regime from Kolmogorov to Kraichnan
turbulence. Our results provide strong evidence that diffuse $\gamma$-ray emission along the Galactic disk is dominated by $\pi^0-$decay emission up to a hundred GeV. These findings provide key insights into the origin of the CR spectral hardening and the propagation of CRs throughout the
Galaxy, and illustrate how this multimessenger approach can be used to probe the origin of features in the CR spectra, such as the long-studied CR Knee.
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All authors Fernando Valenciano, Pedro De la Torre Luque, Daniele Gaggero, Jorge Martin Camalich
Astrophysics of Galaxies
Shock-heated Away: The Impact of Radiative Cooling on Gas-Phase Transitions in Supernova Remnants
Zuzanna Kocjan, Benedikt Diemer, Vadim A. Semenov et al. (+2 more)
Supernova (SN) feedback plays a central role in regulating the structure of the interstellar medium (ISM) through the injection of energy and momentum. The amount of hot gas produced by a
supernova is a key quantity that determines how efficiently SN feedback heats the ISM and drives mass exchange between its different gas phases, here defined as cold ($T < 10^3\, \mathrm{K}$), warm ($10^3\, \mathrm{K} < T < 2\times10^4\, \mathrm{K}$), and hot ($T > 2\times10^4\, \mathrm{K}$) gas. However, previous studies have reported discrepant amounts of hot gas formed under otherwise similar ambient conditions. To resolve these disagreements, we quantify the amount of hot gas produced by individual SN explosions using a suite of controlled simulations spanning a broad range of ISM environments that include both uniform and turbulent, multiphase backgrounds. We show that radiative cooling is a key factor regulating hot-gas production, and that differences in cooling efficiency can account for some of the discrepancies reported in the literature. We derive a simple predictive relation for the peak hot-gas mass attained during the
evolution of a
supernova remnant in terms of the mean ambient density, the initial phase distribution, and the efficiency of gas cooling, which we parameterize as the cooling time over a key temperature range of $10^{4.5}\,\mathrm{K} \lesssim T \lesssim 10^{5.1}\,\mathrm{K}$. Finally, using tracer particles, we distinguish the evaporation of cold and warm gas into the hot phase and derive physically motivated expressions for the evaporation efficiency. Our results provide simple, predictive relations for hot-gas production and phase transitions that can be incorporated into subgrid models of SN feedback in
galaxy formation simulations.
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All authors Zuzanna Kocjan, Benedikt Diemer, Vadim A. Semenov, Shmuel Bialy, Uri Malamud
Astrophysics of Galaxies
Super-Eddington Little Blue Dots May Reionize Helium Too Early
Christopher Cain, Brent Smith, Gibson B. Bowling et al. (+5 more)
The James Webb Space
Telescope (JWST) has identified an abundant population of faint Active Galactic
Nuclei (AGN) at $z \gtrsim 4$ which display broad emission lines, compact morphologies, and blue ultraviolet–optical continua. These “Little Blue Dots' (LBDs) have been suggested to belong to the same family of objects as the more controversial “Little Red Dots' (LRDs), with differences between the two largely owing to viewing angle effects. In this scenario, super-Eddington
accretion resulting in high Extreme UV (EUV) and weak X-ray emission is invoked to explain the properties of both populations. We study the consequences of this super-Eddington scenario for the timing of Helium reionization. We find that observations which support an end to helium reionization no earlier than $z \approx 3$ disfavor scenarios in which the majority of observed $3 \lesssim z \lesssim 7$ LBDs are highly super-Eddington. For our fiducial super-Eddington
accretion scenario, we find that the fraction of the LBD population in this state must be $\lesssim 10\%$, assuming LBDs make up $5\%$ of the $M_{ m UV} < -18$
galaxy population and have average escape fractions of $15\%$, comparable to recent observations. Our constraint assumes that LBDs dominate the Helium reionization budget, and would be tighter if bright
quasars also contributed significantly. For a majority of LBDs to be super-Eddington, they would need to have small escape fractions ($\lesssim 1.5\%$) and/or be less abundant than observations suggest. Our conclusions are sensitive to the shape of the EUV spectra of super-Eddington black holes, motivating further study.
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All authors Christopher Cain, Brent Smith, Gibson B. Bowling, Yongda Zhu, Lily Whitler, Rafael Ortiz III, Anson D'Aloisio, Rogier Windhorst
Astrophysics of Galaxies
The GECKOS survey: Assembly history of the lenticular galaxy NGC 3957
Yuchen Ding, Marie Martig, Ling Zhu et al. (+24 more)
We analyse the assembly history of the edge-on lenticular
galaxy NGC 3957 using deep integral-field spectroscopic MUSE data from the GECKOS survey. By applying a dust-corrected Multi-Gaussian Expansion and a population-orbit superposition model, we disentangle the
galaxy's stellar kinematics, age, and
metallicity. We dynamically decompose the
galaxy and identify three distinct components: a dynamically-cold main disc, a compact Nuclear Stellar Disc (NSD), and a hot component. The NSD emerges as the youngest and most metal-rich component ($t = 6.9 \pm 0.4$ Gyr; $[Z/H] = 0.49 \pm 0.06$ dex), implying that the stellar bar is a long-lived structure that formed at least $\sim 7$ Gyr ago. The main stellar disc is dynamically cold ($\sigma_z \sim 20-30$ km/s), precluding any significant mergers over the last $\sim 8$ Gyr, and exhibits a strong positive age gradient (younger inside, older outside) beyond the bar radius. Synthesising these dynamical fossil records, NGC 3957 likely evolved as a `faded spiral' in a small-to-medium group environment. Its outer disc might passively fade due to mild gas starvation, while the bar fuelled prolonged central
star formation. Comparison with S0s in the Fornax cluster reveals that this combination of internal secular
evolution and mild starvation produces `outside-in' fading signatures that could mimic the environmental stripping typically seen in dense clusters.
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All authors Yuchen Ding, Marie Martig, Ling Zhu, Amelia Fraser-McKelvie, Ryan Leaman, Glenn van de Ven, Jesse van de Sande, Francesca Pinna, Eric Emsellem, Francesca Fragkoudi, Yunpeng Jin, Adriano Poci, Camila de Sá Freitas, Matthew Frosst, Runsheng Cai, Scott M Croom, Timothy A Davis, Rory Elliott, Michael R Hayden, Jesús Falcón-Barroso, Dimitri A Gadotti, Antonino Marasco, Lucas M Valenzuela, Zixian Wang, Emily Wisnioski, Meng Yang, Tayyaba Zafar
Astrophysics of Galaxies
Spatially-Resolved Spectra of Diffuse Galactic Light using 10.8 M DESI Sky Fibers
Andrew K. Saydjari, Bruce T. Draine, Timothy D. Brandt et al. (+49 more)
Using 10.8 million “blank” sky spectra from the DESI Year 3
dataset, we measure the diffuse galactic light (DGL) spectrum in the optical at spectral resolution $R \sim 4000$ by correlating with far-infrared emission from IRAS. Subdividing the sky into 54 deg$^2$ pixels (HEALPix, NSIDE = 8), we map the variation of the DGL correlation spectrum and nebular emission lines across the DESI footprint in the high-Galactic-latitude sky. The increased data volume over previous SDSS-based analyses enables several new detections in the DGL, including scattering both onto and out of the line of sight from neutral interstellar sodium and potassium. We further detect direct emission from ro-vibrational transitions of molecular hydrogen in the near-infrared with an absolute radiance of $0.65\substack{+0.13 \\ -0.12}\times10^{-9}~{\rm erg\, cm^{-2}\,s^{-1}\,sr^{-1}}$, roughly consistent with theoretical expectations, but with an apparent ortho-to-para line ratio that is lower by a factor of $0.60\substack{+0.28 \\ -0.27}$. We confirm previous detections of extended red emission (ERE) in the DGL and map its spatial variation. Our spatially resolved DGL maps provide important observational constraints for the radiative transfer efforts that are now possible with recent 3D models of the Milky Way.
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All authors Andrew K. Saydjari, Bruce T. Draine, Timothy D. Brandt, Edward F. Schlafly, Arjun Dey, Douglas P. Finkbeiner, J. Aguilar, S. Ahlen, C. Allende Prieto, A. Anand, F. Beutler, D. Bianchi, D. Brooks, A. Carnero Rosell, T. Claybaugh, A. de la Macorra, P. Doel, A. Font-Ribera, J. E. Forero-Romero, E. Gaztañaga, Satya Gontcho A Gontcho, G. Gutierrez, J. Guy, K. Honscheid, T. Karim, D. Kirkby, A. Kremin, O. Lahav, A. Lambert, M. Landriau, L. Le Guillou, A. Meisner, R. Miquel, J. Moustakas, S. Nadathur, E. Paillas, W. J. Percival, I. Pérez-Ràfols, F. Prada, C. Ravoux, G. Rossi, L. Samushia, E. Sanchez, C. Saulder, D. Schlegel, M. Schubnell, R. Sharples, J. Silber, M. Siudek, G. Tarlé, B. A. Weaver, R. Zhou
Astrophysics of Galaxies · Cross-listed from astro-ph.CO
AXIS Could Have Accessed Dark Matter Decays
Joshua W. Foster, Inci Karaaslan, Gordan Krnjaic et al. (+1 more)
The Advanced X-ray Imaging Satellite (AXIS) was a mission concept designed to improve upon the sensitivity and spatial resolution of the Chandra X-ray Observatory and XMM-Newton. Although AXIS was not selected for implementation, the concept study defined a mature instrument design with low-background, arcsecond imaging over the $0.3$-$10$ keV energy range, a large effective area, and a wide field of view. These capabilities provide a useful
benchmark for the dark matter decay sensitivity of future X-ray observatories. We estimate the reach of a future AXIS-like instrument for narrow
photon lines from decaying keV-scale dark matter, including
axion-like particles and sterile
neutrinos. For Galactic center observations, we find projected lifetime sensitivities of order $10^{31}$ s, improving upon existing limits by up to an order of magnitude over part of the keV mass range.
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All authors Joshua W. Foster, Inci Karaaslan, Gordan Krnjaic, Nimrod Shapir
Astrophysics of Galaxies
Magnetic destabilisation in disc galaxies: Filament/feather formation
Raghav Arora, Oscar Agertz, Christoph Federrath et al. (+1 more)
Gas gravitational instability plays a crucial role in secular galactic
evolution, but the role played by
magnetic fields in mediating this instability - despite their dynamical relevance and ubiquity - is still not understood. To investigate this question we conduct a parameter study using numerical simulations of 3D isolated disc
galaxies that are initialized in
equilibrium, but have a range of initial magnetisation, quantified by $\beta \in \{0.1, 0.5, 1, 10, 100, \infty\}$, where $\beta$ is the ratio of thermal to
magnetic pressure. We analyse how
magnetic field strength influences the formation of dense filaments and feathers driven by gravitational instability. The simulations show that filament growth rate and spacing are significantly altered by dynamically strong fields ($\beta \lesssim 10$), and that these effects depend on the value of $\beta$ and strength of shear in the disc.
Magnetic fields either stabilise or destabilise, with destabilisation dominating in regions with low $\beta$, and low shear. This makes the destabilisation particularly important in dwarf
galaxies with low-shear rotation curves. Filament spacings are similarly affected differently in different galactic regions, depending upon the local field strength and shear. Our results are in good agreement with predictions from the magneto-Jeans mechanism.
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All authors Raghav Arora, Oscar Agertz, Christoph Federrath, Mark R. Krumholz
Astrophysics of Galaxies · Cross-listed from astro-ph.SR
An All-Sky Catalog of 6.5 Million Primary Red Clump Stars from Gaia DR3 XP Spectra
Zheng Yu and Bingqiu Chen
Red clump (RC)
stars are excellent standard candles for mapping the three-dimensional structure of the Milky Way. We construct an all-sky catalog of 6.5 million primary RC
stars using spectroscopic estimates of asteroseismic parameters inferred from Gaia DR3 low-resolution XP spectra. We train a mixture density network (MDN) on a cross-matched sample. The network maps each 343-dimensional corrected XP spectrum to estimates of $\Delta\Pi_{1}$, the asymptotic period spacing of dipole
gravity modes, and $\Delta\nu$, the large frequency separation. We select primary RC
stars using these two estimates. We release two complementary catalogs defined by different parameter-space cuts and thresholds: a high-purity Tier 1 sample of 532,189
stars with 97% purity and a high-completeness Tier 2 sample of 6,534,931
stars with 86% completeness. Both catalogs cover the full celestial sphere. We provide distances and extinction values for all
stars. We obtain a median photometric distance precision of 6% for Tier 1 RC
stars. Using the resultant distances, we independently calibrate the Gaia DR3 parallax zero-point offset. The three-dimensional density distribution traced by the Tier 2 sample extends continuously to $R\approx25$ kpc. Both catalogs are publicly available. These catalogs provide a valuable resource for Galactic archaeology, delivering a homogeneous
dataset to trace the chemo-dynamical
evolution of the Milky Way and to calibrate models of stellar populations.
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Astrophysics of Galaxies · Cross-listed from astro-ph.HE
Relativistic outflows power a quasi-periodic eruption: constraints on energetics, mass loss, and emission mechanisms
Joheen Chakraborty, Erin Kara, Wenbin Lu et al. (+17 more)
Quasi-periodic eruptions (QPEs) are recurring bursts of X-ray radiation originating from supermassive black holes (SMBHs). They are an unprecedented type of structured, high-amplitude SMBH variability, but the physical origins of their regularity, timescales, energetics, and emission are uncertain. We present new XMM-Newton observations of the QPEs in ZTF19acnskyy/"Ansky", constituting the deepest observations of individual bursts in any source thus far. The X-ray spectra reveal time-evolving P Cygni profiles comprising blueshifted absorption and redshifted emission from L-shell transitions of Fe XIX-XXIV, with column densities $N_H\sim 10^{22-23}$ cm$^{-2}$ and bulk velocities of $|v_w/c|\sim 0.2$, indicating relativistic mass ejections during each eruption. We construct a time-dependent analytical model of a wind turning on to self-consistently compute its evolving luminosity and ionization properties, and find that the light curve and spectral lines can be simultaneously produced by a wide-angle outflow with $\dot{M}\sim 10^{-9}-10^{-8}\,M_\odot$ s$^{-1}$ kinetically powering the X-rays with an efficiency of $L_X/\dot{E}_K\sim 0.1$. For a covering fraction $f_\Omega\sim0.5$, each eruption ejects $\sim 10^{-3}\,M_\odot$ and $\gtrsim 10^{49}$ erg of kinetic energy, setting an upper bound on the QPE lifetime of $\lesssim1000$ bursts if the underlying mass reservoir is $\sim1 M_\odot$, and implying that the bursts may result in detectable multiwavelength signatures of reverberation and feedback. These measurements provide new quantitative constraints on QPE energetics, emission mechanisms, and the mass/energy they recycle into their circumnuclear environments, as well as an observational probe for direct comparison with physical models and hydrodynamical simulations of QPEs.
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All authors Joheen Chakraborty, Erin Kara, Wenbin Lu, Brian D. Metzger, Peter Kosec, Riccardo Arcodia, Itai Linial, Olivia Aspegren, Ehud Behar, Sudip Bhattacharyya, Margherita Giustini, Lorena Hernandez-Garcia, Daniel Kasen, Giovanni Miniutti, Frits Paerels, Erwan Quintin, Claudio Ricci, Daniele Rogantini, Paula Sanchez-Saez, Fatima Zaidouni
Astrophysics of Galaxies
Characterising the Globular Cluster Systems of Three Local Group Dwarf Galaxies: NGC6822, NGC147 and NGC185
Gracie McGill, Annette M. N. Ferguson, Dougal Mackey et al. (+8 more)
We present deep HST photometry for 26 globular clusters (GCs) residing in three Local Group dwarf
galaxies: the isolated dwarf irregular (dIrr)
galaxy, NGC6822, and the M31 dwarf elliptical (dE) satellites, NGC147 and NGC185. From their colour-magnitude diagrams (CMDs), we quantify their red giant branch (RGB) and horizontal branch (HB) morphologies, and employ new empirical relationships to derive measurements of
metallicity, reddening and distance. Additionally, we measure sizes and $V$-band magnitudes from their integrated light profiles. We find that the clusters span a range of
metallicities, from [Fe/H] $\sim-0.7$ to $\lesssim-2$; however, the three dwarfs have very similar mean GC
metallicities ($\sim-1.7$ dex) despite their very different evolutionary histories. In contrast, we find that almost all of NGC6822's GCs exhibit red HB morphologies, whereas those in the two dEs are predominantly blue. We highlight three outlying GCs in NGC6822 that have very low
metallicities yet very red HBs; they are also the most extended clusters in our sample, with half-light radii of $\sim 13-17$pc. If these clusters are young, their origin is difficult to explain given their very remote locations, and
metallicities which are significantly lower than those of the old and intermediate-age
stars in NGC6822. These three clusters are strikingly similar to several GCs linked to substructure in the outer
halo of M31, suggesting either the recent
accretion of an NGC6822-like dwarf by M31, or that both M31 and NGC6822 have recently accreted a similar low-mass system. Additionally, we find compelling evidence that another NGC6822 cluster, SC7, is tidally distorted.
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All authors Gracie McGill, Annette M. N. Ferguson, Dougal Mackey, Chiara Crociati, Jess M. Howell, Avon P. Huxor, Mike J. Irwin, Alan W. McConnachie, Alessandro Savino, Nial R. Tanvir, Daniel R. Weisz
Astrophysics of Galaxies
Dynamical Modeling of Kinematically Decoupled Galaxies: Structural Components
V. S. Goradzhanov, D. D. Mishurin, O. K. Sil'chenko et al. (+1 more)
We present the results of dynamical modeling of two
galaxies with inconsistent kinematics – PGC 35706 and LEDA 2220522 – using data from the MaNGA integral-field spectroscopic survey and deep photometry from the DESI Legacy Imaging Surveys. The Schwarzschild orbit-superposition method in the axisymmetric approximation was employed to identify structural components based on the orbital circularity parameter $\lambda_z$. Three components have been identified in the
galaxies: a spheroidal (bulge/
halo) component and co-rotating and counter-rotating stellar disks. The spheroidal component dominates by mass in both
galaxies: about 60% in PGC 35706 and 51% in LEDA 2220522; the contributions of the co-rotating and counter-rotating disks are 29% and 9% in PGC 35706 and 30% and 18% in LEDA 2220522, respectively. The kinematics of the ionized gas in both
galaxies is consistent with the rotation of the counter-rotating disk, indicating that it formed from externally accreted gas with opposite angular momentum. The results support a scenario in which counter-rotating disks form through gas
accretion from the intergalactic medium or through minor mergers with gas-rich satellites. This work demonstrates the effectiveness of the Schwarzschild method for studying the complex kinematic structure of
galaxies and their formation history.
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All authors V. S. Goradzhanov, D. D. Mishurin, O. K. Sil'chenko, D. F. Gasymov
Astrophysics of Galaxies · Cross-listed from astro-ph.SR
On the Origin of a Dusty Circumstellar Medium around Red Supergiants
Das Sujit, Arkaprabha Sarangi and Sutirtha Sengupta
Red supergiant (RSG)
stars are widely recognized as significant sources of dust, enriching the interstellar medium. However, the physical conditions that regulate dust nucleation in their winds remain poorly constrained. We investigate the formation of molecules and dust in RSG and explore how enhanced mass loss can produce a dense, dust-rich circumstellar medium (CSM) before core collapse. We couple time-dependent mass loss with non-
equilibrium chemistry to model the formation of molecules and dust precursors using mass loss rates ranging from 10$^{-6}$ to 10$^{-2}$ \Mdot\ and both constant and accelerating wind profiles. Molecules such as CO, H$_2$O, SiO, HCN, CS, SO, NH$_3$, H$_2$, and O$_2$ form efficiently in the CSM, with masses varying between 10$^{-15}$–10$^{-2}$ \Ms. O-rich dust, namely silicates and alumina, dominates the dust composition. The total dust mass ranges between 10$^{-8}$ and 3$\times$10$^{-3}$ \Ms. Accelerated winds produce more dust and allow dust formation closer to the stellar surface. The resulting fluxes exhibit strong mid-infrared excesses. The 9.7 and 18 \mic\ silicate features appear in either emission or absorption depending on the optical depth of the circumstellar medium. The time-dependent mass-loss history of our SN~2023ixf progenitor models results in a gradual increase in CSM dust mass toward explosion. A clumpy CSM provides a substantially better match to the observed optical and infrared fluxes, demonstrating the importance of time-dependent mass loss, CSM structure, and wind acceleration in shaping the observable properties of red supergiant progenitors.
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Astrophysics of Galaxies
Deep VISTA observations of the Magellanic Clouds (VMCDeep)
M.-R. L. Cioni, A. O. Omkumar, N. J. G. Cross et al. (+28 more)
The central regions of
galaxies challenge observers with a high density of
stars, gas and dust. The LMC hosts a dense stellar bar whereas the SMC hosts a dense core, which have eluded even the most sensitive large-scale wide-field surveys of individual
stars from the ground and from space. This work describes deep imaging observations obtained with VISTA of the inner regions of the Clouds. They were obtained to resolve
stars fainter than the red clump, that due to crowding were missed in previous observations, and to quantify features associated with the
star formation, kinematics and structure of the
galaxies. These studies will allow us to establish how the dynamical interactions between the LMC and the SMC, and the interaction between the Clouds and the Milky Way have influenced the most gravitationally bound regions. Multiple near-infrared images were obtained in the J and Ks filters during excellent weather conditions. The data were reduced using the VDFS which provides single-filter and band-merged calibrated images and catalogues, with associated confidence maps, for individual observations and combined observations for deep tiles. Approximately one million sources, with only minor quality issues and about 40 epochs per filter, are detected in the central 1.77 sq. deg. They provide a more contiguous spatial area coverage than sources in the VMC survey, which covers the same regions by overlapping two VISTA tiles per
galaxy. The catalogues, which are made available with this work, contain attributes to select unique good quality detections for which we provide examples of ongoing scientific applications. These data represent valuable complementary information to deep imaging observations at other wavelengths and provide additional epochs for proper motion and photometric variability studies extending the time baseline to 11 yr, as well as targets for spectroscopic observations.
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All authors M.-R. L. Cioni, A. O. Omkumar, N. J. G. Cross, F. Cusano, F. Dresbach, F. Ficara, F. Niederhofer, J. M. Oliveira, V. Ripepi, S. Vijayasree, G. Clementini, R. de Grijs, L. Girardi, M. A. T. Groenewegen, V. D. Ivanov, N. Kacharov, M. Marconi, A. Mazzi, G. Pastorelli, C. M. Pennock, M. Petr-Gotzens, J. Storm, S. Subramanian, J. Th. van Loon, R. P. Blake, M. J. Holliman, J. Irwin, M. J. Irwin, R. G. Mann, M. Read, E. Sutorius
Astrophysics of Galaxies
A High Velocity SiO Jet from S255N SMA3
P. D. Klaassen, M. Reiter, Y. Zhang et al. (+2 more)
We present ALMA Band 6 observations of the compact source SMA3 in the S255IR region, analysing both SiO (J = 5-4, 6-5) and CS (J = 5-4) emission to characterise the structure and kinematics of its outflow. The data reveal a highly collimated bipolar jet traced by SiO, reaching line-of-sight velocities of up to $\pm$60 km s$^{-1}$ and de-projected velocities of $\pm$~80 km s$^{-1}$, with a collimation ratio of ~4.7 over a spatial extent of ~5800 au. The inferred dynamical age is 343 yr. Position-velocity diagrams exhibit a continuous velocity structure with triangular morphology, consistent with a steady disk wind rather than an episodic or X-wind-driven flow. Excitation analysis yields a characteristic SiO temperature of ~42 K, and we derive the jet mass, momentum, and kinetic energy which are indicative of a dense, mass-loaded molecular outflow. The emission shows clear chemical and kinematic differentiation: SiO traces the high-velocity jet spine, while CS is observed at lower velocities close to the protostar, and only reaches high velocities at larger distances. Despite forming within a clustered high-mass
star-forming region, the jet exhibits a high degree of
symmetry, collimation, and dynamical coherence more commonly associated with protostars forming in isolation or less crowded
star-forming regions. This demonstrates that well-ordered, narrowly collimated, disk-driven jets can be launched and maintained even in the dense, competitive environments characteristic of high-mass
star formation.
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All authors P. D. Klaassen, M. Reiter, Y. Zhang, K. E. I Tanaka, A. E. Guzman
Astrophysics of Galaxies
Dissecting ultra-diffuse galaxies in the field
A. Vanzanella, K. Malek, Junais et al. (+16 more)
Context. Ultra-diffuse
galaxies (UDGs) in the field are faint, diffuse systems that remain poorly represented in the literature due to the need for spectroscopic confirmation and the difficulty of obtaining high S/N emission line measurements. Aims. We present a spectroscopic study of 17 blue UDG candidates in the field using optical emission lines to confirm their diffuse nature and properties. Methods. We derived spectroscopic
redshifts($z_{\rm spec}$) for our field UDG candidates. We then computed their effective radii ($r_{\rm eff}$) and central surface brightnesses ($\mu_{0,g}$). We measured the H$\alpha$ and H$\beta$ emission line fluxes in the 17 spectra and derived
star-formation rates (SFR) from the line-luminosity relation. We performed forced photometry on our sample to obtain photometric fluxes and applied an aperture correction on the H$\alpha$ integrated fluxes, propagating the correction to the derived SFRs. We then computed stellar masses ($M_*$) using colour relations and estimated dust attenuation and corrected the SFRs accordingly. Two sources were further examined as potential giant low surface-brightness
galaxies(GLSBGs). Results. We identify nine confirmed UDGs, eight other low surface-brightness
galaxies (LSBGs), including one GLSBG. The $z_{\rm spec}$ of our field UDGs span a range of $0.015-0.037$, their $r_{\rm eff}$ spans $1.69-4.99$ kpc and $\mu_{0,g}$ between $24.05-24.98~{\rm mag~arcsec}^{-2}$.
Galaxies exhibit low to moderate dust content, with an average V-band attenuation of 0.29 mag. The spectroscopically confirmed UDGs presented in this work, after the aperture correction performed, lie along the
star-forming main sequence. Conclusions. Our results indicate that blue field UDGs are characterised by heterogeneous dust attenuation and occupy the same region of the
star formation-stellar mass plane as dwarf LSBGs.
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All authors A. Vanzanella, K. Malek, Junais, E. Bernaud, A. Gargiulo, H. Thuruthipilly, K. Lisiecki, A. Pollo, M. Scodeggio, P. M. Weilbacher, S. Boissier, P. Franzetti, G. Lorenzon, A. Nanni, C. Adami, R. Gavazzi, O. Ilbert, S. Pal, N. Principi Cavaterra
Astrophysics of Galaxies · Cross-listed from astro-ph.HE
From Inspiral to Expansion: The Wake-Driven Torque on Binary Black Holes in Gaseous Medium
Jixuan Yang, Lile Wang, Xinyu Li et al. (+1 more)
Binary black holes (BBHs) in gaseous medium, such as active galactic
nucleus (AGN) disks, are important gravitational-wave sources, yet the gas-driven torque that governs their orbital
evolution remains to be fully understood. Most existing studies of BBHs in gas often approximate the net torque as the sum of independent dynamical friction (DF) forces exerted on each black hole by its own wake, neglecting the mutual gravitational coupling between the two wakes. We perform three-dimensional hydrodynamic simulations of circular BBHs in a uniform flow and find the torque is determined by the wake-wake interactions. The net torque is controlled by a single parameter $\eta \equiv v_g/v_o$, the ratio of the gas flow velocity to the binary orbital velocity. At small $\eta$, the wakes merge into a single overdense envelope and the time-averaged torque is negative; as $\eta$ increases, the wakes separate and the torque becomes positive. In AGN disks, capture-channel binaries in a disk model naturally produce $\eta$ in the positive-torque regime; the expansion timescale is comparable to or shorter than the disk lifetime, suggesting that gas-driven expansion can compete with gravitational-wave inspiral and suppress the capture-channel merger rate.
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All authors Jixuan Yang, Lile Wang, Xinyu Li, Rixin Li
Astrophysics of Galaxies
Dense Cores in the Vicinity of an HII Region
Ruofei Zhang, Xing Lu, Jingwen Wu et al. (+23 more)
Massive
stars strongly influence their surroundings through radiative and mechanical feedback, but its effects on dense gas structures at sub-pc scales remain poorly constrained. We investigate how feedback from a newly formed massive
star affects dense cores in the filamentary molecular cloud IRAS 18530+0215. We analyze ALMA Band 6 observations of 1.3 mm dust continuum and DCN, N$_2$D$^+$, and $^{13}$CS line emission, together with VLA K-band continuum and NH$_3$ observations. Dense cores are identified with astrodendro, and their temperatures, masses, velocity dispersions, and virial parameters are derived. The dynamical state of the ultra-compact H II region is examined through energy and pressure estimates. The H II region has a radius of $\sim$0.1 pc and an expansion velocity of $\sim$2.5 km s$^{-1}$, corresponding to a shell dynamical age of $\sim$0.06 Myr. DCN and $^{13}$CS cores are concentrated near the H II region, whereas N$_2$D$^+$ cores preferentially lie farther away. Core temperatures and velocity dispersions decrease with projected distance from the H II region. Virial parameters increase within the inner $\sim$0.3 pc but decline sharply beyond this scale, while core masses show no significant trend with distance. Strong
star formation signatures are found at $\sim$0.2 pc, whereas more distant regions still host quiescent, cold dense cores. The compact H II region appears trapped or choked within $\sim$0.1 pc, while its feedback extends to at least $\sim$0.3 pc. Within this region, feedback enhances core velocity dispersions, gas temperatures, and virial parameters, with no evidence that it promotes the formation of more massive dense cores.
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All authors Ruofei Zhang, Xing Lu, Jingwen Wu, Sihan Jiao, Hauyu Baobab Liu, Guang-Xing Li, Roberto Galván-Madrid, Aiyuan Yang, Siju Zhang, Shanghuo Li, Fengwei Xu, Xindi Tang, Yu Cheng, Weiyuan Zhang, Andrés E. Guzmán, Yuxin Lin, Yuhua Liu, Qizhou Zhang, Patricio Sanhueza, Ke Wang, Siyi Feng, Linjing Feng, Fangyuan Deng, Hao Ruan, Yuanzhen Xiong, Yuxiang Liu
Astrophysics of Galaxies · Cross-listed from astro-ph.SR
Quiescent and Interacting Compact Remnant Binary Populations in the Space Telescope Era
Erin Eastep, Jan J. Eldridge and J. C. Bray
Since the discovery of Gaia BH1, interest in quiescent binary systems has grown. Two additional black-hole binaries have since been discovered alongside several candidate
neutron-
star binaries, yet the formation pathways of these systems remain poorly understood. Theoretical studies of these systems, together with the populations into which they evolve, such as X-ray binaries (XRBs), can help constrain their formation channels. We present predictions for the Galactic population of quiescent binary systems and their later evolutionary phases, including XRBs and post-interaction quiescent binaries. We combine stellar models from the Binary Population and Spectral Synthesis code (BPASS) with a synthetic Milky Way generated using Feedback In Realistic Environments (FIRE) simulations. We compare our results with existing observations to assess how well the synthetic population reproduces the observations. We find generally good agreement, with observed donor masses, compact-object masses, and orbital periods largely reproduced, except for the Gaia BH systems. Our results also suggest that some accreting compact remnants with low-mass donors and wide orbital periods may not be X-ray bright. Remaining discrepancies indicate that the BPASS initial parameter space should be expanded, the common-envelope
evolution prescription revised, and
magnetic braking included in low-mass donor models. We also predict the number of systems detectable in future Gaia data releases and by the Nancy Grace Roman Space
Telescope (hereafter referred to as Roman). In particular, the Galactic Bulge Time Domain Survey is expected to yield a significant population of quiescent black-hole binaries. We predict that ~200-600 candidate quiescent binary systems will be detected in the Galactic Bulge Time Domain Survey, while ~2500-4000 candidate systems will be identified in Gaia DR5.
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