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Physics Astrophysics Astrophysics of Galaxies

astro-ph.GA Watch Astrophysics of Galaxies

Friday 7 August

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

Simplified treatment of kinematic corrections to the SZ effect using the boost operator approach

Alex Hoey, Jacob Long and Jens Chluba

The Sunyaev-Zeldovich (SZ) effects provide a potent cosmological probe of the large-scale structure in the universe. Here, we present a simplified derivation of the kinematic corrections to the relativistic thermal SZ effect using the boost operator approach. By first performing the thermal average inside the moving electron cloud frame, the thermal and peculiar motion contributions can be naturally separated, leading to a significant simplification of the scattering calculation. The angular dependence of the problem is resummed into the pre-computed Doppler operators avoiding the otherwise cumbersome many-dimensional angular integrals required using conventional approaches. We provide expressions for the relativistic SZ signal, exact to all orders in the electron temperature theta_e and the peculiar velocity beta_p of a given cluster. These reproduce well-known results for the relativistic SZ effects and extend the description to higher orders in the cluster's speed. We also derive a closed-form expression for the thermally-averaged thermal SZ scattering operator by studying the underlying symmetries of the Doppler operators fundamental to the formalism. Through these results, we also demonstrate how the boost operator approach gives clarity to the physical description of the problem at hand, promising to be useful to a wide range of astrophysical problems.
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Astrophysics of Galaxies

Tracing the early Milky Way thin disc with the Gaia-ESO Survey

Carlos Viscasillas Vázquez, Sofia Randich, Riano Escate Giribaldi et al. (+3 more)

The origin of metal-poor stars on thin-disc-like orbits remains an open question in Galactic archaeology and provides important constraints on the earliest phases of Milky Way disc formation. We aim to identify and characterise metal-poor stars with thin-disc-like kinematics observed in the Gaia-ESO Survey, using Gaia DR3 orbital parameters, spectroscopic information, isochrone ages, and detailed chemical abundances. Out of 1784 turn-off stars, we identify one metal-poor candidate with [Fe/H] = -1.38 on a dynamically cold, prograde orbit, with low eccentricity, high azimuthal velocity ($V_\phi$ approximately 220 km/s), large angular momentum and low vertical action. Chemically, however, it is clearly distinct from the canonical thin disc: it is $\alpha$-enhanced, with [Mg/Fe] = +0.58 and [$\alpha$/Fe] = +0.48, shows a low [Y/Mg] = -0.58 ratio, and lies on the metal-poor sequence in the [Al/Fe]-[Mg/Mn] plane. The star also has an old age estimate, with a most probable value of about 10.2 Gyr. Its properties suggest that it is not a typical member of the canonical thin disc. Instead, it may be associated with the old thin disc, the metal-weak thick disc, or prograde halo-related populations. This object provides a useful benchmark for studying early metal-poor populations on disc-like orbits.
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All authors Carlos Viscasillas Vázquez, Sofia Randich, Riano Escate Giribaldi, Leda Berni, Laura Magrini, Maria Tsantaki

Astrophysics of Galaxies

CO Structures with Narrow Lines in Nearby Quiescent Regions

Ruilin Xia, Yang Su, Shiyu Zhang et al. (+13 more)

Using CO data from Phase I of the Milky Way Imaging Scroll Painting (MWISP) survey, we present a systematic study of molecular structures with narrow lines. We identify 57 CO structures, most of which exhibit low densities and subsonic/transonic turbulence. Among them, structures with large projected areas and diffuse, sheet-like geometries are identified as veil clouds. The low LSR velocities and the concentration of these CO structures toward both the Galactic center (e.g., Ophiuchus, Aquila) and anticenter (e.g., Cepheus, Taurus) regions suggest a local origin for the sample, as supported by distance measurements of about 200–300pc for a subset with relatively large angular extents. These nearby structures likely arise from large-scale compression driven by past supernova activity within the Local Bubble. The observed low-velocity-dispersion emission may trace quiescent regions where turbulence has decayed due to a lack of sustained energy injection. For diffuse veil clouds with an assumed magnetic field of ~10uG, ion-neutral friction may provide an additional mechanism for turbulent dissipation on sub-parsec scales corresponding to their thickness of 0.1–0.3pc. Tracing the atomic-to-molecular transition, veil clouds provide a unique window into the diffuse, quiescent precursor state of dense gas. They likely represent a widespread but previously overlooked component of the Galactic molecular gas reservoir, with significant implications for cloud formation and evolution, the total mass budget and spatial distribution of molecular gas, and the initial conditions of star formation as a related consequence.
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All authors Ruilin Xia, Yang Su, Shiyu Zhang, Xuepeng Chen, Ji Yang, Yan Gong, Yuehui Ma, Yan Sun, Min Fang, Fujun Du, Shaobo Zhang, Xin Zhou, Lixia Yuan, Qing-Zeng Yan, Li Sun, Jiancheng Feng

Astrophysics of Galaxies

Testing dark matter models and modified gravity theories with spatially resolved HI observations

Federico Lelli, Antonino Marasco, Timothy A. Davis et al. (+8 more)

Understanding the nature of dark matter (DM) is one of the most pressing questions of modern physics. The flat rotation curves of galaxies, especially the extended HI rotation curves from radio observations at 21 cm, played a key historical role to establish the DM problem and continue to be a major tool to test different galaxy formation models, particle DM models, and modified gravity theories. The SKA observatory will revolutionize the study of HI rotation curves thanks to its unprecedented angular resolution, sensitivity, and survey speed. In combination with optical and near-infrared ancillary data, HI surveys with SKA-Mid AA4 will allow us to (1) obtain HI data at spatial resolutions of 1"-2", probing the inner galaxy dynamics with unprecedented details (e.g., the cusp-core problem); (2) move from representative samples of a few hundreds of objects to statistical samples of tens of thousands of objects, allowing us to study the dynamical scaling laws of galaxies and their DM properties with unprecedented statistical power across different cosmic environments; (3) move from galaxies at z~0 to galaxies at z~1, probing DM halos at earlier cosmic epochs and exploring the redshift evolution of the dynamical laws across about 8 Gyrs. The massive SKA data, however, will pose important technical challenges for the derivation of HI rotation curves with automated kinematic software. Developing such kinematic software in the SKA era will be crucial to reach major scientific goals, such as discriminating between different solutions to the DM problem.
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All authors Federico Lelli, Antonino Marasco, Timothy A. Davis, Nathan Deg, Jonathan Freundlich, Gyula I. G. Jòzsa, Peter Kamphuis, Pavel E. Mancera Piña, Stacy S. McGaugh, Amidou Sorgho, Kristine Spekkens

Astrophysics of Galaxies

A Review of Galaxy Quenching – Part II: Theoretical Solutions and Direct Observational Tests

Asa F. L. Bluck

The goal of this review article series is to provide a comprehensive overview of galactic star formation and quenching from both an observational and theoretical perspective. Drawing on a vast quantity of literature, we attempt to answer a deceptively simple question: why do galaxies cease forming stars? In Part II, we concentrate primarily on results from theory and simulations, in addition to direct observational tests of theoretically proposed quenching routes. Over the past two decades, N-body simulations, semi-analytic models, idealized hydrodynamical simulations, cosmological hydrodynamical simulations, and zoom-in hydrodynamical simulations have all provided crucial insights into the fundamental causes and specific mechanisms of galaxy quenching. Throughout this part of the review, we discuss intrinsic routes to massive galaxy quenching from strong baryonic feedback - including supernovae and active galactic nuclei (in both the ejective and preventative modes). Additionally, we discuss dynamical stabilization and the role of mergers. We go on to consider environmental routes to quenching via both ram pressure and dynamical stripping, and as a consequence of the location of satellite galaxies within the cosmic web. We review observational tests of the fundamental causes, specific mechanisms, and triggering of quenching from various techniques. Finally, we conclude this review with tentative answers to the major outstanding issues in this field.
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Astrophysics of Galaxies

A Review of Galaxy Quenching – Part I: Defining the Problem and Observational Results

Asa F. L. Bluck

The goal of this review article series is to provide a comprehensive overview of galactic star formation and quenching from both an observational and theoretical perspective. Drawing on a vast quantity of literature, we attempt to answer a deceptively simple question: why do galaxies cease forming stars? In Part I, we concentrate on observational results, especially from the past two decades, where there have been enormous advances made towards answering this fundamental question. In Part II we focus on theory and simulations, including discussion of direct observational tests thereof. Observationally, the advent of wide-field spectroscopic galaxy surveys, spatially resolved spectroscopy, high resolution sub-mm and radio observations, X-ray observations, the Hubble Space Telescope (HST), and most recently the James Webb Space Telescope (JWST) have all contributed significantly to our empirical knowledge of star formation and its demise in galaxy quenching. We discuss the fundamental problems which quenching aims to solve, various routes to identifying quiescent galaxies in observations, observational constraints on quenching from studies of galaxy populations, and the spatially resolved view of quenching. We end this part of the review with a detailed discussion of the latest results on galaxy quenching at the high redshift frontier from JWST observations.
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Astrophysics of Galaxies · Cross-listed from astro-ph.CO

Redshift Dependence of $H_0$ Dipole in Pantheon+ Supernovae

M.H. Jalali-Kanafi, E. Ó Colgáin, S. Pourojaghi et al. (+1 more)

We examine the dipole structure in the local cosmic expansion rate $H_0$ using the Pantheon+ compilation of Type Ia supernovae. We reconstruct directional maps of $H_0$ across the sky within the low-redshift regime, $z_{\rm min} < z < 0.2$, evaluated in the CMB rest frame. To perform a tomographic analysis, we choose 10 different values for $z_{\rm min}\in [0.015 , 0.045]$ range. We find a dipole amplitude $A_{\rm dip}=1.16\pm0.28\ {\rm km/s/Mpc}$ for the lowest bin, monotonically decreasing to $A_{\rm dip} =0.35\pm0.52\ {\rm km/s/Mpc}$, as we increase $z_{\rm min}$. Since $A_{\rm dip}$ is positive-definite, by construction $A_{\rm dip} > 0$ even in an isotropic universe, thus to assess the statistical significance, we compare to $A_{\rm dip}$ generated from 1000 Monte Carlo simulations based on the $\Lambda$CDM model and the same redshift ranges. Our results reveal a $2-3\sigma$ dipole pattern (depending on how the significance level is computed) for $z_{\rm min}\lesssim 0.032$. For redshift thresholds where the signal remains statistically significant ($>2\sigma$), the inferred dipole direction points close to Shapley supercluster and CMB dipole directions. As $z_{\rm min}$ increases, the dipole amplitude diminishes in line with expectations of a higher redshift isotropic Universe, but the difference in maximal antipodal $H_0$ determinations, $\Delta\text{H}_0^{\rm max}$, retain a signal of an anisotropy that disappears in the dipole ansatz. The decreasing statistical significance of all estimators with increasing $z_{\rm min}$ suggests that any $H_0$ dipole is a low-redshift feature.
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All authors M.H. Jalali-Kanafi, E. Ó Colgáin, S. Pourojaghi, M.M. Sheikh-Jabbari

Astrophysics of Galaxies

Parameter-free prediction of the asymptotic acceleration scale confirmed by weak lensing

Maurice H.P.M. van Putten

The de Sitter transition scale $a_{dS}=cH$ to anomalous galaxy dynamics was previously derived from first principles based on the background Hubble expansion $H$ and the velocity of light $c$. It introduces a $C^0$-transition across $a_{dS}$, which is in tension with predictions of $\Lambda$CDM galaxy models at a significance of $6\sigma$. Tracing late-time cosmology, it predicted the deep-asymptotic acceleration scale $a_0^{th}\simeq 1.66\times 10^{-8}{\rm cm\,s^{-2}}$ without adjustable parameters based on $H$ and the deceleration parameter $q$. A recent weak-lensing determination of $a_0^{WL} = 1.63_{-0.20}^{+0.23}\times 10^{-8}{\rm cm\,s}^{-2}$ now provides an independent empirical test of this prediction. The agreement with the updated theoretical value $a_0^{th} = 1.63_{-0.14}^{+0.13}\times 10^{-8}{\rm cm\,s^{-2}}$ closes the logical chain between cosmology, galaxy dynamics, and asymptotic scaling. Unlike phenomenological fits to rotation curves, this result does not rely on tuning or baryonic modeling but follows directly from background cosmology. This parameter-free model suggests some further tests by galaxy surveys extending over a finite range of redshifts.
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Astrophysics of Galaxies

Formation of globular cluster-rich ultra-diffuse galaxies through mergers

Truman Tapia, Hidenori Matsui, Kenji Bekki et al. (+6 more)

We use high-resolution, idealized hydrodynamic simulations of gas-rich dwarf-galaxy mergers to test whether such encounters can form ultra-diffuse galaxies (UDGs) with globular cluster (GC) systems. We simulate 1:1 and 1:2 mergers alongside an isolated control model and identify stellar overdensities as GC candidates (GCCs). The remnants evolve into dispersion-supported, UDG-like systems with three-dimensional stellar half-mass radii $r^{3D} \sim 1.9-2.6$ kpc, while the isolated dwarf remains rotationally supported and forms no GCCs. Tidal heating and stellar feedback expel a large fraction of the gas beyond the dark matter (DM) halo, leaving stellar-dominated remnants whose DM haloes remain cuspy. Merger-driven star formation is highly clustered: the fraction of newly formed stellar mass bound in massive clusters exceeds 0.5 after the first pericentric passage and remains elevated thereafter. By the final snapshot, the remnants host GC populations numbering 20 (1:1) and 39 (1:2), more centrally concentrated than the field stars and consistent with the observed GC number-halo mass relation. The GCCs match observed star clusters in the planes of mass versus size, velocity dispersion, and density. More massive clusters exhibit stronger internal rotation and broader metallicity spreads. In one case, the merger produces a nucleated UDG via cluster inspiral followed by sustained in-situ star formation. These results demonstrate that gas-rich dwarf mergers are a viable pathway to GC-rich (and sometimes nucleated) UDGs, and predict correlated cluster mass, rotation, and metallicity-dispersion trends testable with observations.
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All authors Truman Tapia, Hidenori Matsui, Kenji Bekki, O. Ivy Wong, Connor Bottrell, Brent Groves, Duncan A. Forbes, Jean P. Brodie, Warrick J. Couch

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

Euclid Early Release Observations of the Barnard 30 dark cloud I. Brown dwarfs and planetary mass candidate members at the core of the association

D. Barrado, H. Bouy, E. L. Martin et al. (+8 more)

This study aims to identify very low-mass members within the Barnard 30 dark cloud, with a particular focus on detecting objects in the substellar domain, including those within the planetary-mass regime. We employed deep photometric observations using data from the Euclid mission, incorporating advanced data processing techniques, in particular the DeNeb tool for optimized source detection. We also analyze multi-wavelength ancillary observations and perform a Spectral Energy Distribution analysis for each candidate member. In addition, low-resolution near-infrared spectroscopy was obtained for one candidate to further assess its nature and properties. Our initial photometric analysis yielded a initial sample of nearly one hundred candidate members in the substellar mass range. A subsample of 23 probable members, located close to the 3 Myr isochrone, has been identified. Thus, we have substantially expanded the known population of faint, cool sources associated with the region. Low resolution near-IR spectroscopic analysis of one candidate reveals an L2 spectral type with low gravity, consistent with a young ultra-cool dwarf. If its membership is confirmed, its estimated mass lies in the range 15-20 Mjup. These findings validate the reliability of our multi-wavelength photometric selection methodology. These results offer valuable insights into the low-mass end of the initial mass function (IMF) and demonstrate the effectiveness of Euclid in identifying brown dwarf and planetary-mass candidates in nearby, densely packed star-forming regions.
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All authors D. Barrado, H. Bouy, E. L. Martin, J.-C. Cuillandre, N. Huélamo, M. Žerjal, C. Dominguez-Tagle, S. Muñoz Torres, J.-Y. Zhang, E. Bertin, J. Olivares

Astrophysics of Galaxies

Smoothed particle magnetohydrodynamics for simulations of galaxy and cosmic structure formation

Orestis A. Karapiperis, Matthieu Schaller, Nikyta Shchutskyi et al. (+2 more)

We introduce a novel formulation of cosmological smoothed particle magnetohydrodynamics (SPMHD), designed to model magnetic field physics in a vast array of nonlinear astrophysical systems, and which we have implemented in the highly-parallel, entirely modular, and open-source simulation code SWIFT. Our numerical scheme is designed to offer optimal performance at a minimal computational cost, keep a low memory footprint, and most notably couple robustly to effective sub-resolution recipes of galaxy formation. This is achieved through expressing our evolution equations in a density-energy conservative form, and augmenting them with discontinuity-capturing terms tailored to high dynamic range simulations, which are further modulated by adaptive switches that drastically improve coupling to sub-grid models and limit spurious dissipation. We moreover present novel suggestions for the two major regularisation techniques used in modern SPMHD, namely a tensile instability correction and mixed hyperbolic/parabolic divergence-cleaning scheme, to ensure code stability in highly dynamical scenarios. We evaluate the performance of our method on a series of problems of increasing complexity, culminating in three astrophysical applications which have historically proven challenging for mesh-less methods: we study jet launching from a forming proto-stellar core, dynamo amplification in a massive galaxy cluster and magnetic field evolution in a Milky Way-like disk galaxy; the latter constitutes the first reported coupling of the EAGLE galaxy formation model to a magnetohydrodynamics solver. Keeping model hyperparameters fixed across our test suite to provide a transparent picture of our method's capabilities in production, we demonstrate sound performance and convergence with resolution on standard `laboratory' numerical experiments, as well as competitive capabilities in realistic applications.
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All authors Orestis A. Karapiperis, Matthieu Schaller, Nikyta Shchutskyi, Federico A. Stasyszyn, Maarten Elion

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

Joint Geometric and Dynamical Constraints on Cosmology from Anisotropies in Galaxy Intrinsic-Alignment Correlations

Teppei Okumura

We present the first joint cosmological analysis to extract both geometric and dynamical information from galaxy intrinsic alignments (IAs). Using BOSS spectroscopy cross-matched with galaxy shape measurements from the DESI Legacy Imaging Surveys, we measure anisotropic galaxy density–intrinsic ellipticity (GI) and intrinsic ellipticity (II) correlations over $0.43\leq z\leq0.7$ and decompose their spin-dependent angular structure into associated Legendre multipoles. The measured GI correlation exhibits the expected baryon acoustic oscillation (BAO) structure, while its anisotropy provides geometric information complementary to galaxy clustering. By jointly modeling redshift-space and Alcock-Paczynski distortions, we constrain the growth rate parameter $f\sigma_8$, the angular-diameter distance $D_A$, and the Hubble expansion rate $H$. Relative to galaxy clustering alone, adding IA reduces their fractional uncertainties by 32%, 18%, and 29%, respectively. By mapping these constraints onto a flat $w_0$CDM model, IA also tightens the constraints on $w_0$, $\Omega_m$, and $H_0$; however, the $w_0$ constraint is sensitive to the minimum scale included in the analysis. Our results establish anisotropic galaxy shapes as an additional source of geometric and dynamical information for spectroscopic cosmology.
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Astrophysics of Galaxies

Detailed Abundance Determination of Metal-Poor Stars with X-Shooter II. - Chemically Disentangling the Halo, Disk and GSE

Benjamin D. C. Lowe, Luca Casagrande, Thomas Nordlander et al. (+2 more)

We present a detailed chemical analysis of seven extremely metal-poor (EMP) star candidates observed with X-Shooter, combining them with 16 EMP candidates from Paper I. We measured abundances for 16 elements, showing excellent agreement with previously published results. The sample was further extended using high-resolution literature data for 315 metal-poor stars. The full sample was then kinematically separated into prograde disk, retrograde disk, Gaia-Sausage Enceladus (GSE) and halo classifications. Combining dynamics with chemistry, we demonstrate that the prograde disk exhibits a distinct negative linear trend in [Sc/Mg] with increasing metallicity, with a slope of -0.6 dex per dex. This contrasts with the halo trend at -0.04 dex per dex, a difference significant at the 3.95$\sigma$ level. Within the metallicity range -4.2 $\leq$ [Fe/H] $\leq$ -1.9, the prograde disk trend is driven by low [Mg/Fe] at lower metallicities, along with low [Sc/Fe] at higher metallicities. This could be due to reduced early Mg enrichment in the progenitor prograde disk, followed by subsequent Mg enrichment, possibly associated with a later gas accretion event. However, the physical origin of the higher-metallicity Sc depletion remains unexplained by current nucleosynthesis models. The result remains significant at the >3$\sigma$ level across kinematic classifications derived from a different Galactic potential. Additionally, we also identified an r-I star with enhanced Ti, moderately-enhanced Sc, and depleted in C (unrelated to its evolutionary state). These abundances suggest a massive jet-induced hypernova progenitor, though a measurement of Zn is needed to verify this.
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All authors Benjamin D. C. Lowe, Luca Casagrande, Thomas Nordlander, Gary S. Da Costa, Norbert Christlieb

Thursday 6 August

Astrophysics of Galaxies

A Detailed Analysis of Intermediate-scale Structure in Optical Extinction Curves: Expanded Census and Two-family Classification

C. M. Gunasekera, M. Decleir, K. D. Gordon et al. (+4 more)

The features of interstellar extinction curves serve as powerful diagnostics for interstellar dust, revealing information about its composition, size distribution, and the physical and chemical processes that shape it. D. Massa et al. reported three faint but wide extinction features, termed intermediate-scale structures (ISS) at 4370, 4870, 6300 Å. Since then, three additional ISS features have been reported in the literature at 7700, 5400, 8500 Å, all with widths greater than any known diffuse interstellar band. We present new optical and UV Hubble Space Telescope/STIS spectra for a sample of 24 early-type OB stars. We used these data combined with 50 literature targets for a systematic, homogeneous analysis of ISS features, with the aim of investigating their observational behavior to help constrain their carriers. This analysis revealed nine more candidate ISS features. We also find that ISS features can be arranged into two main families, which we call $\alpha$ and $\beta$, according to correlations between the feature strengths. Finally, we find strong correlations between the 2175 Å bump strength and ISS features at 4353, 4847, 6443, 7710 Å, suggesting their possible carbonaceous origin.
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All authors C. M. Gunasekera, M. Decleir, K. D. Gordon, G. C. Clayton, B. Günay, D. V. De Putte, P. Yanchulova

Astrophysics of Galaxies

JWST PRIMER: Post-starburst galaxies dominate the low-mass quiescent galaxy population since z~2

Thomas de Lisle, David T. Maltby, Omar Almaini et al. (+10 more)

We present the evolution of the stellar mass functions for photometrically selected star-forming, passive and post-starburst galaxies, based on JWST PRIMER observations of the Ultra-Deep Survey (UDS) field. We identify over 800 post-starburst galaxies within the redshift range 0.5 < z < 3.0. We confirm the presence of a low-mass upturn in the quenched galaxy mass function at log(M*/M_sun) < 10 out to z~2, and show it is primarily driven by post-starburst galaxies. These findings imply that a rapid quenching pathway for low-mass galaxies is already active by z~2, which may be linked to environmental processes. If we assume that all post-starburst galaxies evolve into passive galaxies, adopting a typical visibility time for the post-starburst phase, we find a significant overprediction of low-mass passive galaxies at later times. We suggest a variety of factors that could contribute to reconciling this tension. If low-mass (M* < 10^10 M_sun) post-starburst galaxies quench through slower channels than high-mass systems then the post-starburst phase may be visible for longer periods, reducing their contribution to the passive population. However, the maximum realistic visibility timescale cannot account for all of the excess. We propose that additional factors inhibit the build-up of the low-mass passive galaxy mass function. These galaxies may be removed through mergers or tidal disruption, rejuvenate and return to the star-forming population, or represent systems observed during a dormant phase of stochastic star formation. We conclude that the emergence of the low-mass quenched population is likely governed by a complex interplay of processes, and cannot be explained by simple one-way evolutionary pathways.
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All authors Thomas de Lisle, David T. Maltby, Omar Almaini, Vivienne Wild, Elizabeth Taylor, Kate Rowlands, Guillaume Hewitt, Maya Skarbinski, James S. Dunlop, Adam C. Carnall, Anton M. Koekemoer, Norman A. Grogin, Derek J. McLeod

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

X-rays from shock-heated gas in recurrent-nova remnants: Nested nova shells in a structured circumstellar medium

Sergio Martínez-González, Santiago Jiménez, Richard Wünsch et al. (+1 more)

Recurrent symbiotic novae such as RS Oph show extended X-ray emission associated with the interaction of nova ejecta with the circumstellar environment. We investigate how repeated eruptions over more than a century structure the circumstellar medium and govern the long-term X-ray evolution of a symbiotic recurrent nova. We perform three-dimensional hydrodynamical simulations for a fiducial nine-eruption sequence spanning 130 years, modeling each nova as a supersonic bipolar shell expanding into a wind-shaped circumstellar medium. We post-process the resulting density and temperature distributions to compute X-ray emission in the 0.5-2.0 and 2.0-10.0 keV bands. The eruption sequence excavates a bipolar cavity bounded by nested shells. Soft X-rays trace dense compressed interfaces, whereas hard X-rays arise from the hottest shocked gas, including shell rims and the excavated nova-remnant interior. As the remnant expands, the soft-band emission shows a gradual long-term decline associated with the decreasing emission measure. The hard band evolves episodically, with individual eruptions imprinting distinct flares whose timing and relative strength change as the shell system grows. The extended X-ray morphology becomes progressively smoother and more volume-filling as density contrasts between successive shells are reduced. Our simulations identify extended shell-shock emission as a natural consequence of nested-shell evolution in recurrent novae. Remnant expansion regulates the slow fading of the soft component, and renewed ejecta-shell encounters drive hard-band variability on decade-long timescales. For a fiducial recurrent nova, the predicted diffuse soft X-ray luminosities are broadly consistent with the order of magnitude inferred for RS Oph, indicating that shock-heated gas can contribute appreciably to the observed X-ray environment.
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All authors Sergio Martínez-González, Santiago Jiménez, Richard Wünsch, Tiina Liimets

Astrophysics of Galaxies

Beyond Feedback: Disentangling Baryonic Effects with tSZ$\times$FRB Cross-Correlations

Isabel Medlock and Daisuke Nagai

Standard observational probes lack the sensitivity to characterize the interplay between feedback-driven gas ejection and non-thermal pressure support in groups and clusters, and current models lack the framework to disentangle it. Recent first detections of the tSZ$\times$FRB cross-power spectrum (Takahashi et al, 2025; Sharma et al 2026) have been interpreted as constraining AGN feedback and $\sigma_8$, but the baryon models used do not independently parameterize non-thermal pressure support, leaving feedback efficiency and gas thermodynamics degenerate. We demonstrate that this cross-correlation provides sensitivity to the thermal and non-thermal structure of cluster gas that neither observable alone can achieve, because the tSZ effect traces electron pressure while FRBs trace solely electron density. Using the Baryon Pasting (BP) framework, which separately parameterizes feedback efficiency $\epsilon_f$ and non-thermal pressure amplitude $A_{\rm nt}$, we show that their joint constraint breaks this degeneracy. In the noise-free limit, adding the cross-power spectrum reduces $r_{\rm cond}$ from $0.96$ to $0.08$ (a 12-fold reduction) and improves the joint figure of merit by a factor of 19, with the constraining power concentrated at cluster interior scales ($\ell \gtrsim 3000$). Recent detections are consistent with our fiducial model and disfavor weak feedback ($\epsilon_f^{95\%} \gtrsim 2.40\text{--}3.67 \times 10^{-6}$ across datasets). With $5\times10^4$ FRBs from DSA-2000 combined with SO, we forecast $3.8\%$ fractional precision on $A_{\rm nt}$, improving to $2.3\%$ with CMB-HD. These constraints directly inform the hydrostatic mass bias, with immediate implications for cluster-based cosmological inference from eROSITA, SO, and CMB-HD.
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Astrophysics of Galaxies

Clump Migration in Disk Galaxies: Revisiting Chandrasekhar's Dynamical Friction

Pushpak Pandey and Kanak Saha

Massive stellar clumps are thought to migrate toward galactic centers through dynamical friction, contributing to bulge growth and the structural evolution of disk galaxies. While the classical Chandrasekhar formalism is widely used to estimate clump inspiral times, its validity for extended, evolving clumps embedded in realistic galactic disks remains uncertain. We test this formalism using an isolated disk galaxy simulation by identifying and tracking individual stellar clumps over multiple orbital periods. We develop a position- and mass-based tracking algorithm that follows long-lived clumps and compare their measured orbital evolution with predictions from a dynamical friction model constructed from the simulated baryonic and dark matter mass distributions. After excluding the initial transient phase, we identify nine long-lived clumps, eight of which migrate inward while losing 60-90% of their initial mass. The analytical model reproduces the overall dependence of migration on clump mass and galactocentric radius, but for six clumps it overestimates the inspiral time by factors of $\sim2$-$10$. Since mass loss would reduce the dynamical friction force, it cannot account for the observed faster migration. Our results suggest that additional physical processes, for example clump-clump interactions, non-circular orbits, and the time-dependent disk potential play an important role in regulating clump migration beyond the assumptions of the classical Chandrasekhar formulation.
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Astrophysics of Galaxies · Cross-listed from astro-ph.EP

A Streamer Driving Misalignment in the Circumtriple Disk of GW Ori

Maria Galloway-Sprietsma, Jaehan Bae, Toni Phillips et al. (+5 more)

GW Orionis is a triple stellar system with a disk featuring three misaligned dust rings. We present ALMA molecular line data of CO isotopologues, revealing a streamer feeding the disk in $^{12}$CO and $^{13}$CO. Through multi-pointing observations, we find the streamer extends to $\sim30''$ on-sky ($\sim12,000$~AU) and estimate a mass of 1.6 M$_{\rm Jup}$ using $^{13}$CO. Fitting the morphology and kinematics of the streamer, we estimate the mass infall timescale of 0.04 Myrs and a mass infall rate of $3.6\times10^{-8}$~M$_{\odot}$~yr$^{-1}$, approximately an order of magnitude lower than the stellar accretion rate. Our best-fit trajectory shows that the streamer meets the disk at the outermost dust ring and that the streamer's angular momentum vector is closely aligned with this outermost ring within $\approx3^\circ$, in contrast to the $\approx32^\circ$ misalignment with the innermost ring, suggesting the streamer is the likely cause of the misalignment. However, the total angular momentum of the streamer is smaller than that of GW Ori's disk; this, together with the low accretion rate, indicates that we are probably witnessing the end stages of infall. Total Power observations reveal bright emission connecting the streamer to the surrounding star-forming region, with a projected distance falling well within the Bondi-Hoyle radius, implying the streamer could have originated through Bondi-Hoyle accretion as GW Ori moves through its natal cloud. Together, these results suggest that GW Ori remains dynamically linked to its parental cloud through ongoing accretion, with the streamer serving as the likely driver of its misaligned disk structure.
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All authors Maria Galloway-Sprietsma, Jaehan Bae, Toni Phillips, Jane Huang, Myriam Benisty, Matthew Porter, Christian Ginski, Andrew Winter

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

HI envelope around the carbon star V420 Vul

Xu-Jia Ouyang, Yong Zhang, Chuan-Peng Zhang et al. (+1 more)

We report the detection of an extended 21-cm parsec-scale \ion{H}{i} structure toward the Mira variable V420\,Vul using archival Galactic Arecibo L-band Feed Array survey data. The emission exhibits a spatially coherent but intensity-asymmetric morphology that nevertheless retains a globally symmetric kinematic profile centered near $v_{\mathrm{LSR}} \sim 47.6\,\mathrm{km\,s^{-1}}$. At an adopted distance of $\sim 1.9$\,kpc, the structure extends over $\sim 20$\,pc, implying a dynamical timescale of order $10^6$\,yr. Although the total \ion{H}{i} mass ($\sim 70\,\mathrm{M_\sun}$) indicates that the atomic gas reservoir is heavily dominated by the ambient interstellar medium rather than pristine stellar ejecta, the spatially resolved spectra and position-velocity diagrams reveal an underlying symmetric velocity framework centered on the star. We interpret this as the dynamical imprint of the stellar wind preferentially channeling through a porous ambient cloud, demonstrating that cohesive kinematic records of late-stage stellar mass loss can be preserved over parsec scales and megayear timescales despite dominant interstellar coupling.
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All authors Xu-Jia Ouyang, Yong Zhang, Chuan-Peng Zhang, Li-Yun Zhang

Astrophysics of Galaxies

Mira variable stars in the galactic bulge and halo

Kateřina Neumannová

This work aimed to study Miras in the bulge and halo of our galaxy, including those in globular clusters. The AAVSO International Variable Star Index VSX catalogue was used to retrieve Mira variable stars, while the information about globular clusters were taken from the Harris \citep{Harris1976}, McMaster catalogue \citep{33} and Holger Baumgardt \citep{34} table. Stellar characteristics such as metallicity, $T_{\rm eff}$, parallax and colors were obtained by Gaia EDR3 catalogue, Gaia DR3 VariSumarry, Gaia DR3 catalogue, 2MASS Point Source Catalogue, AllWISE, and ZTF catalogue. The UPSILoN program, color-color or color-magnitude diagrams were used to verify that our stars are indeed Miras-type variable stars and whether they are O or C type Miras. To deal with extinction, which affects stars mainly in the galactic bulge, we used IRSA DUST archive, OGLE-III and recalculation to the extiction-free Wesenheit magnitude. We obtained data for 1608 Miras in the bulge, of which 308 are located in 15 globular clusters. For the stars in the halo, we obtained data for 1954 Miras, of which 4 are located in 3 globular clusters. Miras in the bulge show a bimodal metallicity distribution with peaks at \text{–}0.4 dex and $+$0.5 dex, while Miras in the halo show only one peak at $+$0.5 dex. The period of Miras in the bulge is, on average, 30 days longer than for Miras in the halo, and O-type Miras are more abundant in the bulge than C-type Miras. The dependence of the logarithm of the base 10 period on magnitude in the infrared part of the spectrum gives us a linear dependence, with the dependence inverting when a filter is used in the optical part of the spectrum, because of the dust around the Miras.
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Astrophysics of Galaxies

Luminosity function of quasars at $1.0<z<3.5$ from SDSS and DESI

Gaocheng Yin, Linhua Jiang, Zhiwei Pan et al. (+54 more)

We present a study of the evolution of type 1 quasars at $1.0<z<3.5$, covering the peak epoch of quasar activity. The quasar evolution has been extensively explored by a variety of previous works and the derived quasar luminosity functions (QLFs) are not well consistent with each other, presumably due to the complexities introduced by different quasar selection techniques and associated completeness corrections. We use a new strategy to construct QLFs based on a library of all known quasars. We focus on a wide region of $\sim$1700 deg$^2$ and a deep field of $\sim$265 deg$^2$ that have rich spectroscopic data primarily from SDSS and DESI. We then apply traditional color cuts in the rest-frame UV/optical to select quasar candidates and use the quasar library to identify them. Our final sample consists of 62,426 quasars at $1.0<z<3.5$, with a high completeness ($\sim$96%) and a high purity ($\sim$93%) in the color selection. Simple color cuts can potentially minimize selection biases for the study of quasar evolution. We derive binned QLFs and characterize them using a double power-law model. Sample incompleteness and contamination are considered as part of the uncertainties in the calculation. Compared to previous results, our QLFs are slightly higher at the faint end, and also higher at the bright end at $2.5<z<3.5$. The QLFs suggest that the quasar evolution at $1.0 < z < 2.5$ can be well described by the pure luminosity evolution model, while at $2.5 < z < 3.5$, it can be described by either the pure luminosity evolution or the pure density evolution model.
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All authors Gaocheng Yin, Linhua Jiang, Zhiwei Pan, Paul Martini, Wei-Jian Guo, Siwei Zou, Shengxiu Sun, Swayamtrupta Panda, Abhijeet Anand, Benjamin Alan Weaver, Aaron Meisner, Andrei Cuceu, Arjun Dey, Axel de la Macorra, Christophe Magneville, David Brooks, David Kirkby, David Schlegel, David Sprayberry, Davide Bianchi, Dick Joyce, Enrique Gaztañaga, Eusebio Sanchez, Francisco Javier Castander, Francisco Prada, Gaston Gutierrez, Graziano Rossi, Gregory Tarlé, Hiram K. Herrera-Alcantar, Hu Zou, Ignasi Pérez-Ràfols, Jaime E. Forero-Romero, Jessica Nicole Aguilar, John Moustakas, Joseph Harry Silber, Klaus Honscheid, Laurent Le Guillou, Marc Manera, Martin Landriau, Michael Schubnell, Mustapha Ishak, Nathalie Palanque-Delabrouille, Peter Doel, Ramon Miquel, Robert Kehoe, Satya Gontcho A Gontcho, Seshadri Nadathur, Simone Ferraro, Stephanie Juneau, Steven Ahlen, Theodore Kisner, Todd Claybaugh, Will Percival, Anthony Kremin, Claire Lamman, Claire Poppett, Rongpu Zhou

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

Why do massive stars form bow shocks? Bulk ISM motion as the main driver of bow shock formation and geometry

J. van den Eijnden and L. Kaper

Bow shocks are one the most commonly observed impact sites of massive star feedback. Their existence is often taken as evidence of the supersonic motion or even runaway nature of the massive star. Bow shock geometry is also used to infer the properties of the stellar wind. However, some bow shocks have been reported around sub-sonic massive stars or are orientated differently than the stellar direction of movement, suggesting a substantial influence of the interstellar medium (ISM). In this work, we quantitatively investigate the dominant cause of bow shock formation around massive stars. Starting from an infrared sample of known bow shocks, we measure the stellar peculiar velocities and degree of alignment of the bow shocks. We find that only half ($52\pm2\%$) of the bow shocks is driven by a supersonic star and that $70\pm2\%$ of bow shocks is substantially misaligned (>30 degrees). Of our sample, only $21\pm2\%$ of systems can be regarded as classical bow shocks, driven by a supersonic star in the direction of stellar movement. For the remaining $79\pm2\%$ of systems, the role of bulk ISM movement in creating the shock is equal to or dominant over the stellar movement. We then introduce a new statistical method to derive the magnitude of the ISM motions required to play this dominant role. We find that ISM motion of the order $10-15$ km s$^{-1}$, oriented randomly within the local standard of rest, suffices to explain the existence and orientations of the bow shocks in our sample. For the subset of systems facing HII regions, we find evidence that outflows at $>25$ km s$^{-1}$ from those regions drive the nearby shocks. We conclude that ISM motion is the dominant factor in creating massive star bow shocks and discuss how ignoring these motions can lead to underestimates of the stellar wind's mass loss rate by more than an order of magnitude.
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Astrophysics of Galaxies

Optical Counterparts of MeerKLASS L-band and UHF-band surveys

M. Klein, S. Mangla, J. Mohr et al. (+7 more)

Context: Wide-area radio continuum surveys require reliable optical and infrared counterpart identification, but high optical source densities and extended or multi-component radio morphologies make this challenging. Aims: We present optical and infrared counterpart catalogs for MeerKLASS L-band and UHF-band on-the-fly continuum sources using KiDS DR5 and DESI Legacy Imaging Surveys DR10 (LS DR10), including counterpart probabilities, redshifts, and host-galaxy properties. Methods: We developed the Stellar-mass Enhanced Density Association (SEDA) method, an empirical framework that compares candidate densities around radio positions with those in a position-displaced control catalog. For galaxies we use positional offset, stellar mass, and redshift; quasar candidates are treated separately using offset and mid-infrared selection. A second-pass search associates multi-component radio sources with common hosts. Results: In the L-band survey, we identify 20,400 KiDS-based counterparts with $P_{\rm true}>0.5$, corresponding to 66% of L-band sources within the KiDS footprint. In the UHF-band survey, we identify 61,633 LS DR10 counterparts, corresponding to 81% of the radio sources. Spectroscopic redshifts are available for 22% and 44% of the L-band and UHF-band counterparts, respectively. The redshift distributions show low-redshift star-forming galaxies, intermediate-redshift radio galaxies, and a high-redshift tail dominated by quasars. SEDA also recovers rare radio-loud quasars, including QSO J2318-3113 at $z=6.44$ and UHF_DR1 J+111111.8+053626.6 at $z=5.24$. Conclusions: SEDA provides a data-driven route to counterpart identification for wide-area radio surveys with complex source morphologies. The catalogs enable future MeerKLASS studies of radio source populations, host-galaxy demographics, and rare high-redshift radio quasars.
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All authors M. Klein, S. Mangla, J. Mohr, S. Chatterjee, K. Grainge, S. Paul, M. G. Santos, O. M. Smirnov, C. Tasse, L. Wolz

Astrophysics of Galaxies

Cosmological Distance Measurements of High Redshift Blazars: OJ 248 (z=0.939) and 4C +38.41 (z=1.814)

Young-Bin Shin, Sang-Sung Lee, Sincheol Kang et al. (+3 more)

In this study, we estimated the angular diameter distances to two high-redshift active galactic nuclei (AGNs), OJ 248 (z = 0.939) and 4C +38.41 (z = 1.814), using 43 GHz radio light curves. The aim of this work is to extend AGN variability-based distance measurement methods to the high-redshift regime. The distance estimates were analyzed under two assumptions for the maximum intrinsic brightness temperature TB,int: (1) the equipartition temperature, and (2) the sample-averaged TB,int. As a representative result, when adopting the equipartition temperature, the angular diameter distances to OJ 248 and 4C +38.41 are estimated to be 7592.7 +/- 396.7 Mpc and 11069.8 +/- 1216.9 Mpc, respectively. In addition, Doppler factors were calculated using the inverse-Compton method, and additional distance estimates were obtained based on these values. Our error budget analysis shows that the most significant systematic uncertainty arises from epoch selection. These results indicate that systematic effects have a substantial impact on the derived distance estimates and limit their reliability, particularly in the high-redshift regime. Reducing these uncertainties will require improved observational cadence and reduced post-fit noise. AGN variability provides an alternative approach to distance estimation. However, our results reveal significant limitations in the current methodology and indicate that further methodological and observational improvements are required before its cosmological applicability can be reliably assessed.
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All authors Young-Bin Shin, Sang-Sung Lee, Sincheol Kang, Whee Yeon Cheong, Chanwoo Song, Jeffrey A. Hodgson

Astrophysics of Galaxies

Investigating radio source population and spatial characteristics of diffuse Galactic synchrotron emission in the GAMA-23 field with uGMRT Band-3

Rashmi Sagar, Abhirup Datta and Aishrila Mazumder

We present upgraded Giant Meterwave Radio Telescope (uGMRT) Band-3 observations of the Galaxy and Mass Assembly (GAMA)-23 field. The observations consist of a total of 33 hours spread over 50 pointings, corresponding to $\sim$56 minutes per pointing at the central frequency of 325 MHz. The final image mosaicked from these pointings has a central off-source RMS noise of $109\,\mu\mathrm{Jy}/\mathrm{beam}$ and covers an area $65.31\,\text{deg}^2$ with a resolution of $15.8''$. This wide-area deep-field observation provides a radio source catalog of 5741 sources with flux densities ${\geq}5{\sigma}$. We present complementary uGMRT observations overlapping with the high-frequency Australian Square Kilometre Array Pathfinder Evolutionary Map of the Universe survey. We derived the spectral index from the matched sources in the GAMA-23 field for the first time. We have studied the statistical properties of diffuse Galactic synchrotron emission (DGSE) in the GAMA-23 field using six different latitude target pointings. We fitted DGSE in the form of power law $C_{\ell} = A(1000/{\ell})^{{\beta}}$. Our DGSE amplitude range of $A = 1-20\,{\text{mK}}^2$ and $\beta$ varies between $1.5$ and $2.4$. This work presents one of the first characterizations of DGSE in the southern sky at 325 MHz, setting a precedent for foreground modeling required for sensitive radio observations with the upcoming SKA.
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Astrophysics of Galaxies · Cross-listed from astro-ph.HE

A broadband outburst of the compact steep-spectrum quasar 3C 138 in 2024-2026

T. V. Mufakharov, Yu. V. Sotnikova, V. V. Vlasyuk et al. (+20 more)

After several decades of relative quiescence, the compact steep-spectrum quasar 3C 138 entered an active phase in 2024-2026, exhibiting strong broadband flaring. We investigate its multiwavelength behaviour using dense multifrequency radio monitoring at 1-22 GHz with RATAN-600 and RT-32, optical R-band observations with Zeiss-1000 and AS-500/2, X-ray measurements with Swift/XRT and SRG/ART-XC, and the Fermi-LAT $\gamma$-ray light curve. The radio brightening accelerated after 2022 and was strongest at the highest frequencies. The radio spectra hardened markedly, with the 11-22 GHz spectral index evolving from steep to flat or inverted during the active phase. The X-ray flux increased by more than a factor of three during 2025-2026, while the photon index hardened from $\Gamma_{\rm X}\simeq 1.6$ to $\Gamma_{\rm X}\simeq 0.9$ and softened back after the peak. Flare decomposition revealed five $\gamma$-ray flares and a sequence of optical subflares during the later stages of the activity. The $\gamma$-ray, X-ray, and optical maxima occur within a $\simeq 13$-day interval, suggesting a common activity episode, whereas the radio brightens more gradually and in a frequency-dependent manner. Under the adopted compact-zone geometries, the sparse two-state spectral energy distributions (SEDs) can be represented by one-zone synchrotron self-Compton (SSC) solutions, while the relative contribution of external Compton (EC) remains geometry dependent. The flare shifts the modelled energy partition towards relativistic electrons. These results favour a longer-lived, core-dominated activity phase, with later high-energy and optical flares superposed on the opacity-driven radio evolution of an emerging synchrotron component.
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All authors T. V. Mufakharov, Yu. V. Sotnikova, V. V. Vlasyuk, S. Yu. Sazonov, M. L. Khabibullina, A. G. Mikhailov, A. B. Pushkarev, T. An, Y. A. Kovalev, Y. Y. Kovalev, A. V. Popkov, M. A. Kharinov, G. S. Uskov, I. Yu. Lapshov, E. V. Filippova, A. Yu. Tkachenko, K. V. Iuzhanina, A. K. Erkenov, R. Yu. Udovitskiy, O. I. Spiridonova, I. A. Rakhimov, T. S. Andreeva, A. A. Ogloblin

Astrophysics of Galaxies

Ruffled Feathers: Merger-driven galaxy size growth and structural transformation in EAGLE

Kai Wang, Carlton Baugh, Sownak Bose et al. (+9 more)

Galaxy mergers drive both the size growth and the transformation from discs to spheroids, yet the prescriptions used to model these processes in semi-analytic frameworks have not been tested against the realistic merger population in cosmological hydrodynamical simulations. Using $\approx 4{,}500$ mergers identified in the EAGLE simulation, we test an energy-conservation estimator for post-merger galaxy sizes and quantify merger-driven morphological transformation. The predicted remnant half-stellar-mass radius matches the simulated descendant size with a scatter of $\approx 0.12$-$0.15$ dex and no significant systematic dependence on progenitor properties, while a commonly used dissipation correction applied to gas-rich mergers under-predicts the post-merger size by up to $\approx 0.4$ dex in a cosmological context and increases the overall scatter. The per-merger size growth increases monotonically with the stellar mass ratio of the merging pair, from $\lesssim 0.03$ dex for minor mergers to $\approx 0.10$ dex for equal-mass mergers. From the energy-conservation estimator, we analytically derive the size growth efficiency per unit accreted stellar mass, $\eta \equiv \mathrm{d}\log_{10} r_{\star}/\mathrm{d}\log_{10} M_{\star}$, and show that $\eta$ reaches $\approx 2$ only in the idealised limit of collisionless minor mergers with zero orbital energy; as $\eta$ is highly sensitive to the orbital energy at the time of merging, the minor merger channel cannot be established as the driver of the rapid size growth of massive galaxies without better constraints on this quantity. Beyond the size growth, mergers systematically reduce rotational support and increase triaxiality in proportion to mass ratio, but even the most nearly equal-mass mergers do not always fully destroy the disc, in tension with the complete disc destruction assumed in several semi-analytic models.
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All authors Kai Wang, Carlton Baugh, Sownak Bose, Shaun Cole, Carlos S. Frenk, Cedric Lacey, Shengdong Lu, Peder Norberg, Isabel Santos-Santos, Francesco Shankar, Tom Theuns, Tao Wang

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

Photometric Distances for Metal-poor Giants and a Search for Hypervelocity Stars with LAMOST DR13 and Gaia DR3

Shuai Xu, Haibo Yuan, Bowen Huang et al. (+2 more)

Hypervelocity stars (HVSs) are stars with velocities high enough to escape the Milky Way, but their identification depends sensitively on distance estimates, particularly for distant giants. In this work, we search for metal-poor HVS candidates by combining LAMOST DR13 spectroscopy with Gaia DR3 astrometry. We calibrate a metallicity-dependent color–absolute-magnitude relation for normal metal-poor giants using a high-quality reference sample, and apply it to derive photometric distances for 41{,}331 stars. The relation reproduces the reference absolute magnitudes with a scatter of 0.24\,mag, corresponding to an intrinsic distance uncertainty of $\sim$9.7%. Combining these distances with Gaia proper motions and LAMOST radial velocities, we identify 13 initially unbound candidates under the Galactic potential from \citet{McMillan2017}. Spectral inspection indicates that several are chromospherically active binaries or other non-standard systems for which a giant-star calibration is unreliable; removing these contaminants leaves nine metal-poor HVS candidates. Backward orbit integrations suggest that one candidate is most consistent with a disk origin, while three have trajectories suggestive of an association with the Sagittarius stream.
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All authors Shuai Xu, Haibo Yuan, Bowen Huang, Xiao Kai, Wuming Yang

Astrophysics of Galaxies

An ALMA study of hub-filament systems II.Quiescent filaments converging towards highly dynamic hubs

Michael Anderson, Nicolas Peretto, Sarah E. Ragan et al. (+7 more)

Hub-filament systems are networks of converging interstellar filaments, often with active star formation at their centres, that may play an important role in high-mass star formation. In Anderson et al. (2021) we found that the mass fraction that ends up in a clump's most massive core is significantly higher in IR-dark hubs than IR-bright clumps, suggesting that the most-massive cores form early on. Such early massive core formation requires large inflow rates and dynamically active IR-dark clumps. We now present N$_2$H$^+$(J=1-0) observations of six IR-dark hub-filament systems mapped with ALMA 12m+7m+TP at $\sim 3''$ resolution, to trace the kinematics of the dense gas. The data show intricate emission structures and complex spectra. To characterise their kinematics, we have developed mwydyn, a fully-automated, multiple velocity component, hyperfine line-fitting code. Our results reveal that the emission invariably consists of quiescent individual filaments in the outskirts that converge towards the hub centres where a systematic increase in velocity dispersion and number of components is observed. We also find that the distribution of centroid velocities is remarkably similar between clumps, despite spanning more than one order of magnitude in mass. We propose that our results are best explained by the mixing of gravitationally-driven multi-directional inflows, resulting in highly complex and dynamic hub centres. We also discuss the implications of the observed differentiated filament and hub gas kinematics in the context of the 3D morphology of hub-filament systems.
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All authors Michael Anderson, Nicolas Peretto, Sarah E. Ragan, Andrew J. Rigby, Adam Avison, Ana Duarte-Cabral, Gary A. Fuller, Yancy L. Shirley, Alessio Traficante, Gwenllian M. Williams