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Physics Astrophysics Astrophysics of Galaxies

astro-ph.GA Watch Astrophysics of Galaxies

Monday 12 October

Astrophysics of Galaxies

Evidence for Hierarchical Turbulent Scaling in Nearby Star-Forming Galaxies

Luna Maria Scipio, Fernando A. N. Santos and Jay Armas

We find recurring signatures of intermittency in molecular-gas velocities from cloud to galactic scales. In 31 selected galaxies from PHANGS-ALMA, velocity-centroid exponents through sixth order show nonlinear order dependence and nearly linear relations between consecutive exponents across galaxies. Positive estimated offsets from single-exponent scaling occur in all 52 galaxies with a valid power law fit and 99 of 100 clouds. A generalized She-Leveque hierarchy accommodates these signatures, supporting a hierarchical description of turbulent scaling in molecular gas across these environments.
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Astrophysics of Galaxies

Environmental Dependence of Satellite Planarity and Orbital-Pole Coherence around Milky Way Analogues in a Hydrodynamical Cosmological Simulation

Peng Wang, Yu Luo, Jiang Chang et al. (+2 more)

We examine whether the unusual spatial flattening and orbital-plane coherence of the Milky Way's classical satellites are connected to the Galaxy's location in the cosmic web. We compare the 11 classical satellites with the 11 most massive satellites of 11,922 Milky Way-mass hosts in the TNG300-1 hydrodynamical simulation. We measure flattening with both the simple inertia tensor (SIT), which retains radial information, and the reduced inertia tensor (RIT), which isolates angular anisotropy. Orbital-plane coherence is characterized by the minimum opening angle containing the axes of the eight most coplanar satellite orbits. For the Milky Way, we find $(c/a,b/a)=(0.183,0.558)$ for SIT and $(0.364,0.736)$ for RIT, together with an eight-orbit opening angle of $21.9^\circ$. The corresponding fractions of simulated systems at least as extreme are $4.94\%$, $12.28\%$, and $5.04\%$, respectively. We describe the environment using the velocity-shear tensor smoothed on $2\,h^{-1}\mathrm{Mpc}$ and compare the full sample with Local Group-like pairs, systems whose shear eigenvalues match those reconstructed for the Local Group, and hosts in knots, filaments, sheets, and voids. Among the well-sampled environmental subsets, the shape and opening-angle distributions differ only weakly. Although the cosmic web imprints preferred orientations on host spins and satellite orbital-plane axes, the Milky Way combines orientations that are uncommon in the simulation. We conclude that the present-day cosmic-web environment alone does not substantially increase the occurrence of Milky Way-like satellite configurations. This result does not rule out an origin in anisotropic accretion, since neither the present-day web class nor its shear eigenvalues fully encodes the assembly history of an individual satellite system.
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All authors Peng Wang, Yu Luo, Jiang Chang, Xi Kang, Shi Shao

Astrophysics of Galaxies

Identifying the principal mechanism of star formation feedback

Chong Li, Rouyu Li, Keping Qiu et al. (+27 more)

Feedback from massive stars regulates the formation of next-generation stars and planets and thus shapes the evolution of galaxies, yet observational evidence capable of determining which mechanism dominates the feedback process has long been lacking. Here,we present a large-scale HI survey toward Orion A$.$ With an unprecedented sensitivity and superior resolution, FAST (Five-hundred-meter Aperture Spherical radio Telescope) reveals a well-defined heart-shaped expanding HI bubble, enshrouding the well-known "Veil" bubble of ionized gas. The photoionization-driven and wind-driven gas expands at 10.9 and 13.8 kilometers per second, respectively, with a kinetic energy ratio of 1:2 assuming a spherical symmetry and a uniform HI-to-H2 ratio. This first direct comparison within a single bubble shows that radiation does not dominate the feedback process as predicted by classical theories; instead, stellar winds contribute a comparable share of the injected kinetic energy.
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All authors Chong Li, Rouyu Li, Keping Qiu, Marko Krco, Di Li, Hongchi Wang, Xin Lyu, Yan Duan, Min Fang, Xuepeng Chen, Lile Wang, Haoran Feng, Shuinai Zhang, Miaomiao Zhang, Shaobo Zhang, Yue Cao, Yao Wang, Yan Gong, Fujun Du, Zhiwei Chen, Yang Su, Yuehui Ma, Yuchen Xing, Yinghui Zheng, Tianwei Zhang, Shu Niu, Chenrui Li, Jiawei Liu, Zhijun Zhang, Yulian Guo

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

Blackbody evolution and circumstellar medium properties of broad-lined H-rich superluminous supernovae

Tuomas Kangas, Takashi Nagao, Uliana Pylypenko et al. (+2 more)

Broad-lined H-rich superluminous supernovae (SLSNe II) tend to show signs of interaction, including a UV excess compared to a blackbody function. However, a quantitative analysis of the CSM configuration and the UV excess has so far not been performed for most of the literature sample. Additionally, SN 2023gpw showed signs of asymmetry in its peculiar blackbody and spectral evolution, raising the question of whether similar properties can be found in other SLSNe II. We aim to characterize the circumstellar environment of SLSNe II by searching for signs of asymmetry, quantifying the UV excess, and investigating any IR echoes produced by dust. Diversity among SLSNe II is also explored. We fit blackbody functions to the SEDs of SLSNe II to quantify the UV excess luminosity and its evolution. We use this to investigate mass-loss rates required to produce the excess through interaction. We also investigate the line profiles in SLSN II at late times and compare line velocities to the blackbody radius evolution. We examine public WISE IR images and place constraints on IR echoes. We find mass loss rates of $\sim10^{-4}$ to $\sim0.03\, \mathrm{M_\odot}$~yr$^{-1}$ when assuming all interaction luminosity emerges in the UV, i.e., conservative lower limits for the total mass loss rate. Radii calculated from line velocities in late-time spectra are mostly too large for a spherical interaction photosphere, only compatible with the blackbody radius evolution if the CSM is non-spherical with a low filling factor. This is in some cases supported by a mismatch between spectroscopic and blackbody expansion velocities. Considerable diversity is seen in the sample, probably as a result of different viewing angles and CSM masses. WISE images seem too shallow to observe IR echoes in SLSNe II beyond $z\sim0.1$, but in the nearest event, SN 2020jhm, a likely IR echo is detected, suggesting pre-existing dust.
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All authors Tuomas Kangas, Takashi Nagao, Uliana Pylypenko, Steve Schulze, Lin Yan

Astrophysics of Galaxies

Nearly pristine gas in a galaxy 1 billion years after the Big Bang

Sarah E. I. Bosman, Frederick B. Davies, Louise Welsh et al. (+22 more)

Excitation of carbon and oxygen ions is the primary mechanism by which collapsing gas clouds dissipate heat to form new stars. At early cosmic times, in galaxies with chemically pristine gas, many stars are expected to have masses far larger than the mass of our sun due to the deficit in these elements. We searched for ultra-metal-poor galaxies using their spectroscopic absorption signatures in front of bright background quasars, employing the new GHOST high-resolution spectrograph. Here we report the discovery of the first galaxy containing a reservoir of neutral hydrogen gas with metallicity below the ultra-metal-poor threshold: with a measured carbon-to-hydrogen ratio 11,000 times lower than the Sun, it is the most pristine ever found by a factor of four. UMP-DLA-1 is the only known galaxy with measured carbon and oxygen abundances too low to enable efficient formation of stars with solar mass or below. The low metallicity alone therefore guarantees a top-heavy stellar population, providing a direct view of the chemical composition imprinted by massive low-metallicity stars that perished long before the present day: an elevated oxygen-to-carbon ratio. The abundance pattern of UMP-DLA-1 is likely a close representation of the atomic yields of first- or early second-generation stars.
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All authors Sarah E. I. Bosman, Frederick B. Davies, Louise Welsh, Emanuele P. Farina, Prakash Gaikwad, Benedetta Spina, Barun Maity, Ryan Cooke, Klaudia Protušová, Valentina D'Odorico, Eduardo Bañados, James S. Bolton, Rebecca L. Davies, Xiaohui Fan, Martin G. Haehnelt, Joseph F. Hennawi, Tahlia J. Hill, Seyeon Hwang, Vid Iršič, Laura Keating, Girish Kulkarni, Samuel Lai, Emma V. Ryan-Weber, Lasse Seyberlich, Molly Wolfson

Astrophysics of Galaxies

Galaxy Clusters from the DESI Legacy Imaging Surveys. IV. Alignment of Member Galaxy Orientations at z < 0.5

Zhaobin Chen, Yizhou Gu, Shufei Liu et al. (+2 more)

Using DESI photometric catalog data, we systematically analyze the spatial alignment of star-forming galaxies (SFGs) and quiescent galaxies (QGs) in clusters. The results reveal that, in both brightest central galaxy (BCG) alignment (BA) and satellite alignment (SA), the alignment signals of SFGs and QGs exhibit opposite trends in several aspects. For the BA signal, SFGs show stronger alignment in cluster outskirts, whereas QGs exhibit stronger alignment in inner regions. For the SA signal, both SFGs and QGs exhibit nearly isotropic signals in outer regions, while in inner regions they show opposite signals. In addition, the BA signal depends on cluster richness and QG fraction, and is more pronounced in mature clusters. Specifically, QGs show a stronger BA signal overall, which increases with luminosity and axis ratio, whereas SFGs show a weaker BA signal with no significant dependence on these parameters. The BA signal also exhibits a strong dependence on satellite galaxy color, which is independent of morphology. We confirm this by analyzing the BA signal in two populations: red disk and blue elliptical galaxies. However, neither BA nor SA shows a significant dependence on redshift at z < 0.5. In summary, these findings reflect how galaxy transport along cosmic filaments drives cluster evolution: early-stage SFGs fall into clusters along filaments, and during cluster relaxation, their spatial orientations are reshaped by gravitational potentials and tidal forces, weakening BA signal and enhancing SA signal. In contrast, QGs, as early cluster members, exhibit a more pronounced anisotropic distribution and maintain relatively stable spatial orientations.
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All authors Zhaobin Chen, Yizhou Gu, Shufei Liu, Hu Zou, Qirong Yuan

Astrophysics of Galaxies

Intrinsic Soft X-ray Emission from the Hot Circumgalactic Medium in IllustrisTNG

Minjae Kim and Junhan Kim

We study the intrinsic 0.5–2~keV emission of the hot circumgalactic medium (CGM) in the IllustrisTNG simulation TNG100-2 at redshifts 0, 0.1, and 0.2. We calculate the emission of gas cells with $T \geq 10^6$~K in the spherical shell between $0.15R_{500}$ and $R_{500}$ and compare samples selected by their star-formation activity. X-ray luminosity increases with halo mass, although the class-dependent fits cover different mass intervals. Among galaxies with positive luminosity and star formation rate (SFR), the high-activity sample retains a positive association after a linear adjustment for halo mass. The residual association is weaker in the quiescent subset with positive luminosity and SFR. Within $10^{11.75}<M_{500}/M_\odot<10^{12.25}$, the high-activity sample has more centrally concentrated emission and a median luminosity about five times that of the quiescent sample. The two populations have similar median hot-gas masses despite their different X-ray luminosities and radial profiles. These differences are consistent with variations in the spatial distribution and thermodynamic state of the emitting gas, although the samples are not matched in halo mass. Our results suggest that soft X-ray emission probes the structure of the hot CGM as well as its gas content, offering a way to investigate how star formation and feedback shape gaseous halos.
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Astrophysics of Galaxies

WALLABY pilot survey: accurate and automated linewidth measurements from global HI profiles

Shinna Kim, Tobias Westmeier, Lister Staveley-Smith et al. (+11 more)

Current-generation 21-cm surveys of extragalactic neutral hydrogen (HI) with instruments such as FAST and ASKAP are providing detailed spectral and spatial information for over 10^5 galaxies. Future HI surveys with next-generation radio telescopes could provide sample sizes larger by orders of magnitude. There is therefore a need for accurate, automated, and reliable parameterisation of the HI emission from galaxies. We have developed an automated estimator for HI global profile widths to better enable studies of, for example, dynamical masses and Tully-Fisher distances. Our estimator is based on an implementation of the BusyFit profile-fitting algorithm, and converges for 95% of global profiles in the WALLABY pilot survey. Probability density functions are calculated for all profile parameters using Monte Carlo techniques, and example error parameterisations are given. We confirm that linewidth uncertainties depend primarily on the integrated signal-to-noise ratio, profile steepness, and the linewidth, consistent with previous studies. We compare several common linewidth definitions, and the width at 50% of the mean flux density (Wm50) is found to be the most robust measure of linewidth. We provide examples of the baryonic Tully-Fisher relation drawn from the WALLABY pilot survey.
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All authors Shinna Kim, Tobias Westmeier, Lister Staveley-Smith, Danail Obreschkow, Barbara Catinella, Nathan Deg, Karen Lee-Waddell, Jonghwan Rhee, Kristine Spekkens, O. Ivy Wong, Matthew Colless, Hélène M. Courtois, Boyi Ding, Bumhyun Lee

Astrophysics of Galaxies

TractorJAX: GPU-Accelerated SPHEREx Forced Photometry and the Trade-offs of Regularization and External Priors

Hyeonguk Bahk and Ho Seong Hwang

We present TractorJAX, an open-source GPU reimplementation of the catalog-forced mode of The Tractor. We use it to test whether regularization or external flux priors enable reliable fitting of reference catalogs that extend below the depth directly constrained by undersampled SPHEREx images. For full-depth regularized fits, TractorJAX fits $100\times100$-pixel cutouts at 11.9 ms each on a single NVIDIA H100 GPU. In simulated images of the Abell 2537 galaxy-cluster field, extending the fitted catalog from $m_z<21$ to the full DESI Legacy Imaging Surveys DR10 catalog increases the scatter in fractional flux residuals by 34%, even with regularization. We also test the methods using SPHEREx observations in nine fields, assessing the number of reliably measured sources and photometric-redshift accuracy. Requiring S/N $>5$ in more than half of the 102 channels, we find that the regularized full-depth fit yields 40% fewer sources than the truncated fit. For sources meeting this requirement in both fits, the normalized median absolute deviation of the photometric redshifts, $\sigma_{\rm NMAD}$, is 17% larger in the full-depth fit. External flux priors recover nearly as many sources as the $m_z<21$ fit, but increase $\sigma_{\rm NMAD}$ by 0.0015 for the common calibrated sample. Neither regularization nor the external flux priors tested here simultaneously preserve the sample size and photometric-redshift accuracy achieved by the truncated fit. Our results suggest that the optimal fitted-catalog depth cannot be determined from image-level performance alone, but should be selected through end-to-end tests tailored to the intended science measurement.
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Sunday 11 October

Astrophysics of Galaxies

Constraints on the r-process Delay Time from Dwarf Spheroidal Galaxies

Lauren E. Henderson, Evan N. Kirby, Mithi A. C. de los Reyes et al. (+1 more)

The ancient stellar populations and simple structure of the local dwarf spheroidal galaxies (dSphs) make them excellent laboratories for studying the chemical evolution of the early universe. In this paper, we fit one-zone galactic chemical evolution models to C, Mg, Si, Ca, Fe, Sr, Y, Ba, and Eu abundances in the dSphs Sculptor and Draco. By including the s- and r-processes in our model, we are able to place constraints on the timescale of r-process enrichment in these dSphs. We find that neutron star mergers cannot be the only source of the r-process in Sculptor and Draco, and that a prompt r-process source is required to explain the observed stellar abundances. When neutron star mergers are the only source of the r-process in our models, their minimum delay time must be just 14-16 Myr. The neutron-capture abundances in Sculptor and Draco can also be fit by models with a longer neutron star merger minimum delay time combined with a prompt r-process source that operates on the same timescale as massive star evolution, such as magneto-rotational supernovae. Additionally, the Sr and Y abundances in the dSphs set limits on the Sr and Y yields per r-process event. We find that theoretical r-process yields overestimate Sr and Y production by a factor of up to 100.
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All authors Lauren E. Henderson, Evan N. Kirby, Mithi A. C. de los Reyes, Rebecca Surman

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

An asteroseismic age estimate for the Pleiades using a neural-network emulator of rotating $\delta$ Scuti pulsation models

Anuj Gautam and Simon J. Murphy

Asteroseismology of $\delta$ Sct stars has strong potential for determining the ages of young stars through individual mode fitting. We present a neural-network emulator trained on approximately 46 million rotating pulsation models. From stellar mass, metallicity, age, and equatorial rotation velocity, it predicts 12 classical observables, two asteroseismic scalars, and the p mode, f mode and low-order g mode frequencies for degrees $\ell=0$-3, including the individual $m$ components of rotationally split multiplets. We couple the emulator to nested sampling through a multivariate likelihood that propagates correlated emulator residuals, making full Bayesian posterior exploration practical. Applied to five $\delta$ Sct stars in the Pleiades observed by TESS, the framework gives mutually consistent individual asteroseismic ages of 107-117 Myr. Combining their age posteriors gives a cluster age of $113.3\pm4.5$ Myr (statistical), consistent with the $112 \pm 5$ Myr lithium-depletion-boundary age and the 110-160 Myr range from rotating-isochrone fitting. Together with spectroscopic $v\sin i$, the inferred equatorial velocities also provide post-fit inclination estimates. Separate perturbed-grid tests using 100 matched synthetic pairs per input-physics variation give median absolute age shifts of $2.1$, $2.3$, and $5.2$ Myr for $|\Delta f_{\rm ov}|=0.005$, $|\Delta\alpha_{\rm MLT}|=0.1$, and $|\Delta Y|=0.02$, respectively; the corresponding 90th percentile shifts are $6.5$, $7.6$, and $16.2$ Myr. These tests describe conditional population sensitivities, not a systematic uncertainty on the Pleiades age. Together, the cluster-age agreement and the scale of these input-physics sensitivities support $\delta$ Sct asteroseismology as a complementary age estimation method for young stars.
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Astrophysics of Galaxies

The DAWN JWST Archive: A spectroscopically-informed population study of the physical properties of galaxies at z>2

Rashmi Gottumukkala, Gabriel Brammer, Sune Toft et al. (+30 more)

Charting the evolution of star-formation, stellar mass and dust build-up over cosmic time relies on the accurate characterisation of the stellar population properties of high redshift galaxies. We present a catalogue of spectroscopically derived physical properties for ~12,000 galaxies at z>2, with archival JWST/NIRSpec PRISM spectroscopy and JWST/NIRCam imaging from the DAWN JWST Archive. We present a custom version of the SED fitting code BAGPIPES, used to perform joint spectrophotometric modelling of PRISM spectra and broadband NIRCam photometry. In doing so, we publicly release a science-ready catalogue of the physical properties of galaxies beyond cosmic noon. We report key physical properties, such as stellar masses, star-formation rates (SFR) and timescales, and V-band dust attenuation (Av). We further probe the recent star-formation histories (SFH) of galaxies via their SFRs on 3 Myr, 10 Myr, and 100 Myr timescales, capturing both rising and falling recent SFHs. Through dust-corrected ugi colour-colour diagrams of massive galaxies, we show how quiescent and dusty galaxies populate this colour space at z>2, with galaxies experiencing a recent downturn in star-formation occupying distinct parameter space. We also study the dustiest galaxies in our sample, showing that they are preferentially more massive and strongly star-forming relative to the parent sample, residing on the high-mass end of the star-forming main-sequence. The slope of the attenuation curve has a strong dependence on Av, varying from steep to shallow as the dust attenuation increases and the specific star-formation rate decreases. Our findings show that the unparalleled number statistics of this catalogue of spectroscopically derived stellar population properties uniquely enables the study star-formation, quenching and dust properties of galaxies from cosmic noon to cosmic dawn.
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All authors Rashmi Gottumukkala, Gabriel Brammer, Sune Toft, Mengyuan Xiao, Anna de Graaff, Pascal A. Oesch, Francesco Valentino, Katherine E. Whitaker, William M. Baker, Laia Barrufet, Rachel Bezanson, Leindert A. Boogaard, Alex J. Cameron, Olivia R. Cooper, Emma Giovinazzo, Kasper E. Heintz, Michaela Hirschmann, Kei Ito, Ivo Labbe, Minju M. Lee, Zach J. Lewis, Jorryt Matthee, Ian McConachie, Desika Narayanan, Clara L. Pollock, Sedona H. Price, David J. Setton, Marko Shuntov, Pieter van Dokkum, Bingjie Wang, Joris Witstok, Yunchong Zhang, Pengpei Zhu

Astrophysics of Galaxies

The Tilt of the Velocity Ellipsoid in the Milky Way Disk with GALAH-Gaia Data

Zhenzhen He, Ruilan Yang, Hui Li et al. (+1 more)

We investigate the metallicity dependence of the tilt of the velocity ellipsoid using more than 572,000 stars selected from GALAH and Gaia. We find that the tilt angles of disk stars can be well described by the relation $\alpha = \alpha_{0}\,\mathrm{arctan}(Z/R)$, and the $\alpha_{0}$ differ significantly among different disk populations, with $\alpha_{0}$ are 0.78 $\pm$ 0.05, 0.86 $\pm$ 0.07, and 0.77 $\pm$ 0.07 for the whole sample, the Low-[$\alpha$/Fe] and the High-[$\alpha$/Fe] populations, respectively. These results indicate that Galactic disk populations are globally tilted toward cylindrical alignment, implying that the gravitational potential of the Galactic baryonic disk plays a dominant role in shaping the kinematics of dynamically relaxed stars. Our detailed analysis further reveals a metallicity dependence of $\alpha_{0}$ for various populations, with the Low-[$\alpha$/Fe] and the High-[$\alpha$/Fe] populations are respectively $\alpha_{0}$ = 0.12 $\mathrm{sin}$(3.72 [Fe/H] + 1.09) + 0.75 and $\alpha_{0}$ = 0.20 $\mathrm{sin}$(2.99 [Fe/H] + 1.90) + 0.71. These results indicate that the metallicity dependence observed in the Low-[$\alpha$/Fe] population may be primarily associated with resonances induced by the Galactic bar, while the behavior of the High-[$\alpha$/Fe] population may also have been affected by additional dynamical and evolutionary processes, such as violent heating associated with mergers, accretion, and/or the formation of these stars in an environment shaped by mergers of gas-rich systems and/or a turbulent ISM.
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All authors Zhenzhen He, Ruilan Yang, Hui Li, Weixiang Sun

Astrophysics of Galaxies

Modelling the broken age-[Fe/H] relation and metallicity distribution function of mono-age populations

Qinhao Shao and Jianhui Lian

This study investigates the chemical evolution history and radial migration in the Milky Way utilizing high-precision age measurements based on large-scale stellar spectroscopic surveys. Recent observational data have revealed a distinct break in the age-metallicity relation of stars in the solar neighborhood, suggesting that stellar populations of the Milky Way can be divided into two evolutionary sequences. Based on galactic chemical evolution models, we confirm that this break in the age-metallicity relation can be explained by a recent major gas accretion event, which diluted the metallicity in the disk and triggered a starburst, leading to the formation of an independent age-metallicity sequence. To assess the impact of stellar radial migration, we incorporate a simplified treatment of this process into our multi-zone chemical evolution model. Radial migration is modeled as a probabilistic diffusion process, characterized by a Gaussian distribution. By fitting the model-predicted metallicity distribution functions (MDFs) of mono-age stellar populations to observations, we infer a migration strength of $\sigma = 2.15^{+0.100}_{-0.103}\,{\rm kpc}$ for stars with ages between 2 and 6 Gyr located at 9.5-11.5 kpc, corresponding to an average radial displacement of 1.92 kpc over 10 Gyr. This result is lower than previous estimates of stellar radial migration, suggesting that the role of radial migration in shaping the chemical structure of the Milky Way is less important than previously estimated.
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Astrophysics of Galaxies

Anisotropic Radiation in Super-Eddington Active Galactic Nuclei: The Responsivity of Broad-Line Regions to Continuum Variability

Feng-Na Fang, Pu Du and Jian-Min Wang

Anisotropic ionizing radiation is a natural theoretical expectation for super-Eddington accretion in active galactic nuclei (AGNs), implying that the ionizing flux incident on the broad-line region (BLR) clouds differs from that measured along the observer's line of sight. Reverberation mapping studies have revealed systematically shortened time lags of the broad H$\beta$ emission line relative to continuum variations in super-Eddington AGNs, a phenomenon that can be naturally interpreted as a consequence of anisotropic ionizing continuum radiation. To further investigate this anisotropy, we perform a systematic analysis of the H$\beta$ line responsivity, defined as the ratio of the variability amplitude of H$\beta$ to that of the driving continuum, for both sub- and super-Eddington AGNs. By combining the effective responsivities measured relative to the driving continuum, after correcting for the continuum–emission-line delay, with photoionization calculations, we infer the ionizing radiation field received by their BLRs. We find that, in super-Eddington AGNs, the ionizing flux inferred from the H$\beta$ responsivity differs significantly from that observed along the line of sight, whereas the two are in closer agreement in sub-Eddington AGNs. These results provide compelling evidence for strong anisotropy of the incident ionizing radiation in super-Eddington AGNs. We conclude by discussing the broader implications of this anisotropy, including its potential relevance to the "little red dots" recently discovered by the James Webb Space Telescope.
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Saturday 10 October

Astrophysics of Galaxies

The NIVARIA-Local Group simulations: Unveiling the origin of rotation curve diversity in dwarf galaxies and its connection to galaxy morphology

A. Contreras-Santos, A. Di Cintio, A. Negri et al. (+7 more)

Dwarf galaxies exhibit a large diversity in rotation curve shapes, challenging galaxy formation models within the $\Lambda$CDM paradigm. We present NIVARIA-LG, a new suite of cosmological simulations studying dwarf galaxy evolution in realistic Local Group environments. This intermediate-resolution pilot lays the groundwork for the full-scale NIVARIA project. The simulations combine constrained Local Group initial conditions from HESTIA with the NIHAO galaxy formation model. The simulated galaxies reproduce observed stellar-to-halo mass relations, match the Baryonic Tully-Fisher relation, and capture the distribution of stellar effective radii, including compact and diffuse galaxies. We analyse the structural and kinematic properties of isolated dwarf galaxies with $10^7 \lesssim M_\star/M_\odot \lesssim 10^{10}$, focusing on rotation curve diversity. NIVARIA-LG naturally produces a broad range of rotation curve shapes, including slowly rising systems underrepresented in previous simulations and steep rotation curves. We find that rotation curve diversity is primarily associated with gas extent and inner dark matter structure: more extended gas and shallower inner density profiles correspond to more slowly rising curves, while stellar effective radius shows little independent association. Individual galaxies show that rotation curve shapes change rapidly as gas is redistributed during assembly. Recent accretion events are also associated with more slowly rising curves in the most massive dwarfs. Together, these results suggest that rotation curve diversity is linked to the baryonic cycle, which shapes the inner dark matter distribution. The Local Group environment and its filaments influence this evolution by regulating gas accretion and redistribution, producing the observed diversity in rotation curve shapes.
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All authors A. Contreras-Santos, A. Di Cintio, A. Negri, J. Sarrato-Alós, S. Cardona-Barrero, G. García-Bethencourt, C. Brook, N. I. Libeskind, A. Knebe, A. Macciò

Astrophysics of Galaxies

Photometric Identification and Dynamical Purification of Blue Horizontal Branch Stars in DESI MWS DR1

Shuai Zhang, Xiaolong Wang, Kai Xiao et al. (+5 more)

Blue horizontal-branch (BHB) stars are ideal tracers for mapping the structure of the Galactic stellar halo. However, traditional spectroscopic identification is limited by data quality and sample size, while broad-band photometric methods often achieve only moderate completeness and purity. Building upon the color-space BHB identification method of \citet{2025ApJS..278...62H}, we synthesize SkyMapper $(u,v,g,z)$ photometry from DESI MWS DR1 spectroscopy and identify 9,237 BHB candidates in the $(g-z)_0$–$(u-v)_0$ color space using the HDBSCAN clustering algorithm. We then construct a Kernel Density Estimation (KDE) Bayesian probability model with capture-recapture (C-R) prior to assign posterior membership probabilities, achieving a probability-weighted purity of 88.9% and completeness of 94.2%. Applying an escape-velocity cut based on the Galactic gravitational potential, we remove 1,461 contaminants with unphysical kinematic parameters, yielding a clean photometric BHB sample $\mathcal{S}_c$ of 7,776 stars (retention rate $R_{\rm keep} = 84.2\%$). Systematic analysis of the contaminants reveals that they are predominantly faint sources ($g\sim20$~mag) with very low signal-to-noise ratios (median SNR~$<$~5). When the BHB color–luminosity relation is incorrectly applied to these objects, their space velocities are amplified beyond the Galactic escape limit, confirming that the escape-velocity filter essentially acts as a physical detector of low-SNR–driven distance inflation.
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All authors Shuai Zhang, Xiaolong Wang, Kai Xiao, Guozhen Hu, Wenyuan Cui, Ce Cai, Shuai Feng, Jie Ju

Astrophysics of Galaxies

The Galactic disk structure revealed by Gaia XP spectra

Zhenkang Tang, Jianhui Lian, Jialong Zhou et al. (+1 more)

The spatial structures of chemical populations constrain Galactic disk evolution and its underlying physical processes. Gaia XP spectra provide one of the largest spectroscopic samples available. We use Gaia XP spectra to study Galactic disk mono-abundance populations (MAPs), measuring their scale heights as a function of radius and radial surface-mass-density profiles. We construct a red giant branch (RGB) sample and divide it into MAPs according to $[\alpha/{\rm M}]$ and $[{\rm M/H}]$. The sample covers a $6\times6$ kpc region centered on the Sun in the Galactic plane and extends to $|Z|<3.7$ kpc. We estimate XP completeness using a Gaia photometric parent sample and combine PARSEC isochrones with a Kroupa initial mass function (IMF) to calculate the selection function and convert observed stellar counts into intrinsic stellar mass densities. We fit vertical density profiles with an exponential model to derive scale heights and integrate the fitted profiles to obtain surface mass densities. The resulting profiles are generally consistent with those from APOGEE. All MAPs show flaring, with the high-$\alpha$ population exhibiting the strongest flaring and the metal-poor and sub-solar low-$\alpha$ populations showing the weakest. Surface-mass-density profiles differ significantly among MAPs: the high-$\alpha$ and metal-rich low-$\alpha$ populations show approximately exponential declines, whereas the other low-$\alpha$ populations exhibit plateau-like features, indicating that the Galactic disk cannot be described by a simple single-exponential profile. These differential structures suggest a complex Galactic disk assembly history likely regulated by birth conditions, secular dynamical heating, radial migration, and external perturbations.
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All authors Zhenkang Tang, Jianhui Lian, Jialong Zhou, Jiadong Li

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

The $R$-Process Alliance: On J0010$-$1735, an Accreted, Chemically Unusual, Metal-poor Star with $R$-process Enhancement

Zoe Hackshaw, Rana Ezzeddine, Shivani P. Shah et al. (+11 more)

We present a detailed chemo-dynamical analysis of the chemically peculiar very metal-poor ([Fe/H]$=-2.22\pm 0.11$) Milky Way (MW) halo star, 2MASS J00101758$-$1735387 (hereafter J0010-1735), discovered by the $R$-Process Alliance. We derive abundances for 45 elements, including 28 neutron-capture elements, and confirm that \thestar\ is highly $r$-process-enhanced, with [Eu/Fe]=$+1.30$. The light, $\alpha$, and Fe-peak element abundances ratios relative to Fe are all sub-solar, aside from C, Si, and most extremely, Ca. We investigate three possible formation scenarios based on the star's chemical abundances and orbital kinematics: whether it formed in the in-situ MW halo, in a MW dwarf galaxy satellite, or in a satellite of the Magellanic Cloud system. Using the position of \thestar\ in the [Mg/Mn]–[Al/Fe] plane, the abundance pattern of both the light and heavy elements, and the kinematics, we conclude that J0010-1735 most plausibly originated in a now-disrupted ultra-faint dwarf galaxy that was accreted into the MW halo. We examine potential chemical enrichment scenarios of J0010-1735, including one similar to the $r$-process-enhanced UFD Reticulum II, or enrichment via a sub-Chandrasekhar Type Ia SNe, potentially supplemented by a Ca-rich gap transient and by a separate neutron-rich site that facilitated $r$-process enrichment. A nuclear cosmochronometric age of $12.5\pm4.2$ Gyr is derived from the [Th/Eu] ratio, consistent with an ancient origin in one of the earliest star-forming systems in the universe.
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All authors Zoe Hackshaw, Rana Ezzeddine, Shivani P. Shah, Terese T. Hansen, Ruijie Shi, Yangyang Li, Timothy C. Beers, Anna Frebel, Erika Holmbeck, Alexander P. Ji, Jeremy Kowkabany, Vinicius M. Placco, Ian U. Roederer, Charli M. Sakari

Astrophysics of Galaxies

Multiphase Analysis of (U)LIRG Nuclear Activity (MAUNA). I. Spatially Resolved Optical Emission-Line Diagnostics

Justin A. Kader, Vivian U, Marina Bianchin et al. (+33 more)

We present resolved optical integral-field spectroscopy of the 32 luminous and ultraluminous infrared galaxy systems of the Multiphase Analysis of (U)LIRG Nuclear Activity (MAUNA) sample, drawn from the GOALS survey and selected to have JWST/MIRI medium-resolution spectrometer (MRS) observations. The data set combines new Keck/KCWI observations of 10 systems with archival VLT/MUSE cubes for 22 systems, covering H$\beta$ to [S II] at ~1 arcsecond spatial resolution (~0.9 kpc at the sample median distance). Using the optical [N II]/H$\alpha$ BPT diagram, we find that composite and LINER-like excitation together account for most of the classified area (median fractions 0.44 and 0.26), while Seyfert-like gas covers a median fraction of 0.02 but carries a far larger proportion of the line luminosity where it is present. Both the projected size of the Seyfert-classified region, $R_{\rm Sy}=0.08$-$7.5$ kpc, and its [O III] luminosity increase with the bolometric AGN luminosity, with $R_{\rm Sy}\propto L_{\rm AGN,bol}^{0.54\pm0.18}$, as expected for gas photoionized at a constant ionization parameter. The scatter about the luminosity relation depends on dust opacity: the [O III] luminosity per unit AGN luminosity falls by $1.09\pm0.25$ dex per unit depth of the 9.7 $\mu$m silicate absorption feature (Spearman $\rho=-0.60$, $p=0.001$). Optical excitation diagnostics therefore locate AGN-excited gas reliably but systematically underestimate the luminosity the AGN supplies to the host in the most obscured (U)LIRGs.
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All authors Justin A. Kader, Vivian U, Marina Bianchin, Yiqing Song, George C. Privon, Sabrina Stierwalt, Tanio Diaz-Santos, Lee Armus, Vassilis Charmandaris, Ezequiel Treister, Rosalie McGurk, Hanae Inami, Jeffrey A. Rich, Sean T. Linden, Anne M. Medling, Loreto Barcos-Muñoz, Gabriela Canalizo, Aaron S. Evans, Kirsten L. Larson, Tianmu Gao, Thomas Lai, Laura Lenkic, Jaya Nagarajan-Swenson, Justin Howell, Cristina M. Lofaro, Matthew A. Malkan, María Sánchez-García, Christopher D. Martin, Mateusz Matuszewski, Claire E. Max, Joseph M. Mazzarella, James D. Neill, Nikolaus Z. Prusinski, Raymond Remigio, David Sanders, Jason Surace

Astrophysics of Galaxies

Beyond the Damped Random Walk: Multiband AGN Variability from SDSS to Rubin LSST

Izak Schmidlkofer, Zhirui Hu, Weixiang Yu et al. (+1 more)

The flux variability of Active Galactic Nuclei (AGNs) is commonly modeled using the damped random walk (DRW), but increasingly rich multiband time-domain surveys motivate more flexible stochastic models that characterize variability beyond a single timescale and exploit dependence across bands. Multivariate continuous-time autoregressive moving average (MCARMA) processes extend the multivariate DRW to higher-order stochastic dynamics and provide a matrix-valued power spectral density for characterizing marginal variability and cross-band dependence. In a carefully selected Sloan Digital Sky Survey (SDSS) Stripe~82 sample, higher-order models are selected for 109 of 134 AGNs (81.3%), with substantial rather than marginal support in most objects; convergence diagnostics indicate that this fraction is conservative. The fitted models also reveal strong cross-band dependence that generally decreases with wavelength separation. Motivated by this richer structure, we investigate its recoverability under Vera C. Rubin Observatory Legacy Survey of Space and Time (LSST) observing conditions. Model-order recovery depends strongly on the underlying stochastic behavior as well as source brightness and observing cadence. Recovery is high across many of the simulated settings, but deteriorates when the characteristic features of higher-order variability become difficult to distinguish from the multivariate DRW. Additional simulations show that this loss of distinguishability can persist over a range of underlying variability behaviors. These results show that stochastic structure beyond the multivariate DRW is prevalent in our selected SDSS sample, while its recoverability with LSST depends on both observational conditions and the form of the underlying stochastic variability. The methodology is implemented in the Python package mcarma.
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All authors Izak Schmidlkofer, Zhirui Hu, Weixiang Yu, Hyungsuk Tak

Friday 9 October

Astrophysics of Galaxies

Globular cluster Observations for Luminosity-dispersion Distances (GOLD): Project description and velocity catalogue

K. Fahrion, M. A. Beasley, A. Gvozdenko et al. (+10 more)

We introduce and describe the Globular cluster Observations for Luminosity-Dispersion distances (GOLD) project, which has the principal aim of determining independent distances based on the globular cluster (GC) absolute magnitude-velocity dispersion ($M_V - \sigma$) relation calibrated with Milky Way GCs with Gaia distances. The project comprises observations of GCs in 19 early- and late-type galaxies taken with FLAMES/GIRAFFE on ESO's Very Large Telescope. So far, 17 galaxies have been observed. The spectra cover the wavelength range 8483-9000 AA, including the calcium triplet region at a spectral resolution of $R\sim18,000$. The spectra provide line-of-sight velocities with typical uncertainties of $\Delta v = 1-2$ km s$^{-1}$. Using primarily velocities to separate extragalactic sources from foreground stars, we present here our initial sample of 1062 GCs and 101 ultra-compact dwarf galaxies (UCDs). For more than 650 of these objects we present the first velocity measurement. We discuss the available photometry and size measurements, and show that our velocities are in good agreement with previous studies. Our velocity catalogues are made publicly available. Beyond the principal aim of obtaining precision distances, additional science to be explored with these data includes host galaxy halo dynamics and clustering analysis, mass-to light ratios of GCs and UCDs in the sample, the stellar initial mass function and black hole occupation fraction of the GCs, and chemical abundances from high-dispersion spectra.
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All authors K. Fahrion, M. A. Beasley, A. Gvozdenko, I. Ortega-Casas, A. Ferre-Mateu, F. I. Aros, D. Dold, T. Jerabkova, S. S. Larsen, O. Müller, M. Rejkuba, K. L. Rhode, G. van de Ven

Astrophysics of Galaxies

Stellar discs and intermediate-mass black holes in galactic nuclei II. Fragmenting the disc and forming the S-stars in a live nuclear star cluster

Taras Panamarev and Bence Kocsis

We present direct $N$-body simulations of a stellar disc around the supermassive black hole Sgr~A*, perturbed by an intermediate-mass black hole (IMBH) and embedded in a live nuclear star cluster. A retrograde IMBH with $m_\bullet=2000\,M_\odot$, relative inclination $\theta_\bullet=150^\circ$, and initial semi-major axis $a_\bullet=0.15$~pc breaks the disc into three disc-like components and an angular momentum filament. The stochastic torques of the cluster, together with the IMBH's inward migration, increase the angular separation between these substructures. By ${\sim}5$~Myr, their separations become comparable to those among the observed Galactic-centre young star structures. The innermost ($a\le0.04$~pc) disc stars evolve into an S-star-like population. Relaxation driven by the cluster disperses their orbital planes, excites their eccentricities and depletes the `zone of avoidance' within ${\sim}10$~Myr even without an IMBH. The IMBH further accelerates their orbital-plane reorientation. However, the most eccentric S-stars may require an additional formation channel, such as the Hills mechanism. The distinctive signatures of the IMBH are the well-separated disc components and the eccentricity excitation confined to the radial range swept by its orbit. Dynamical friction from the cluster reduces the orbital size of a $2000\,M_\odot$ IMBH initially at $0.15$~pc by more than a factor of two within $10$~Myr. Prograde IMBHs tend to align with the stellar disc, whereas a $2000\,M_\odot$ retrograde IMBH can anti-align with the radially overlapping disc stars. We also quantify how the IMBH affects the supply of stars to the loss cone and the rates of stellar tidal disruptions and binary separations.
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Astrophysics of Galaxies

Searching for Nearby Supermassive Black Hole Binaries with GRAVITY

GRAVITY Collaboration: K. Abd El Dayem, N. Aimar, A. Berdeu et al. (+81 more)

We present a systematic interferometric search for close supermassive black hole (SMBH) binaries in 20 nearby type 1 active galactic nuclei (AGN) observed with VLTI/\grav. We investigate parsec-scale asymmetric emission by modeling the squared visibilities and closure phases with a single circular Gaussian component plus a background point source for the central AGN, and searching for additional compact companions through grid-based binary models. The robustness of the search is validated using injection-recovery simulations and point-spread-function diagnostics. Several features are identified in the initial significance maps, but only one candidate out of 20 shows a persistent compact asymmetry, corresponding to an observed incidence of $5\%$. If NGC~3783 is interpreted as a binary AGN, we derive a Poissonian one-sided $1\sigma$ upper limit of $f_{\rm bin}<16.5\%$ for GRAVITY-detectable binaries among bright nearby AGN (K<12.5) at separations of $\sim1$-$100$~pc. Conversely, if the observed asymmetry in NGC~3783 is associated with asymmetric circumnuclear dust emission, the corresponding upper limit on the binary fraction is $f_{\rm bin}<9.2\%$. We compare these results with predictions from the Horizon-AGN simulation, finding comparable binary fractions. We also noted that the expected fraction strongly depends on the assumed distribution of individual SMBH accretion rates within binaries, which is currently unresolved in cosmological models. Our results demonstrate the potential of infrared interferometry to identify parsec-scale binary AGN candidates and motivate future GRAVITY+ observations to expand the sample and follow up known candidates, helping to confirm their nature and distinguish genuine binaries from asymmetric nuclear structures.
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All authors GRAVITY Collaboration: K. Abd El Dayem, N. Aimar, A. Berdeu, J.-P. Berger, G. Bourdarot, W. Brandner, Y. Cao, C. Correia, Q. D'Amato, R. Davies, D. Defrère, A. Drescher, F. Eisenhauer, M. Fabricius, H. Feuchtgruber, S. Flesch, N. M. Förster Schreiber, A. Foschi, Q. Fournier, P. Garcia, R. Garcia Lopez, R. Genzel, S. Gillessen, F. Gonté, X. Haubois, S. F. Hönig, L. C. Ho, M. Houllé, S. Joharle, J. Kammerer, A. Kaufer, P. Kervella, J. Kolb, L. Kreidberg, L. Labadie, S. Lacour, O. Lai, R. Laugier, J.B. Le Bouquin, J. Leftley, R. Li, K. Li, B. Lopez, D. Lutz, F. Mannucci, F. Mang, A. Mérand, F. Millour, M. Montargès, N. Morujão, H. Nowacki, M. Nowak, S. Oberti, J. Osorno, T. Ott, C. Paladini, S. Pappert, T. Paumard, K. Perraut, G. Perrin, R. Petrov, P. O. Petrucci, N. Pourré, S. Rabien, D. C. Ribeiro, S. Robbe-Dubois, M. Sadun Bordoni, J. Sanchez-Bermudez, J. Sauter, M. Scialpi, J. Scigliuto, J. Shangguan, T. Shimizu, F. Soulez, C. Straubmeier, E. Sturm, M. Subroweit, C. Sykes, L. J. Tacconi, P. Thévenet, I. Urso, F. Vincent, J. Woillez, G. Zins

Astrophysics of Galaxies

A first view of interstellar Fe-bearing dust grains with XRISM

I. Psaradaki, L. Corrales, E. Costantini et al. (+8 more)

Understanding the reservoirs of iron (Fe) in our Galaxy is crucial for probing the mechanisms that drive dust grain growth in the interstellar medium (ISM). High-resolution X-ray absorption spectroscopy offers a powerful tool to investigate the chemistry of dust grains, particularly those containing Fe, through spectroscopic features near photoabsorption edges known as X-ray Absorption Fine Structures (XAFS). With the Resolve spectrometer aboard XRISM, we can now examine the Fe K-edge (7.1 keV) owing to its improved spectral resolution in this energy range. This enabled us to probe the dust grain chemistry in high Galactic column densities. In this work, we present a pilot study on dust grain chemistry through the Fe K-edge of the XRISM Performance Verification target GX 340+0. This source is a persistently bright low-mass X-ray binary with a hydrogen column density of 6.6x10^22 cm^-2 along the line of sight, providing sufficient optical depth at the Fe K-edge. By fitting combined dust and gas models, we find that Fe is depleted by 95% into dust along the line of sight towards the source. Moreover, we find evidence that 38% of the solid-phase Fe is in metallic iron, 47% in iron sulfides, and the remainder in silicates. The large contribution from metallic iron and iron sulfides differs from what is typically inferred from X-ray studies of diffuse ISM and may suggest that that these compounds become more significant reservoirs of Fe in higher column density Galactic sightlines.
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All authors I. Psaradaki, L. Corrales, E. Costantini, M. Mehdipour, D. Rogantini, H. Takahasi, R. Ballhausen, P. Chakraborty, T. Nakagawa, R. K. Smith, S. Zeegers

Astrophysics of Galaxies

Cluster Ages to Reconstruct the Milky Way Assembly (CARMA). VI. The age-metallicity relation of in-situ clusters and the age of the Universe

Chiara Zerbinati, Davide Massari, Fernando Aguado-Agelet et al. (+11 more)

Within the homogeneous framework for the derivation of GC ages defined by the CARMA collaboration, we focus on the clusters born in-situ in the MW. As they are the oldest among the old GCs, their absolute age provides constraints about the age of the Universe. Moreover, the shape of their AMR is expected to show the imprints of past merger events, in case these were able to trigger GC formation in the Galaxy. We derive new homogeneous ages for 18 GCs dynamically and/or chemically classified as in-situ, and build the MW AMR from a total sample of 34 GCs. We find that all the selected GCs follow a well defined AMR, with the exception of NGC6642 and Pal1. While the former is likely a member of the LKH merger event, thus putting chronological evidence for the existence of this progenitor on even more robust ground, for the latter we propose an alternative scenario according to which it formed in-situ, but in a metal-depleted region of the Galaxy, possibly due to the interaction with an unspecified merger event. To find evidence of merger-driven GC formation, we use a GMM for the observed age distribution. This is statistically best-fit by 4 components, which we associate with significant events of the MW merger history. Cluster ages were finally calibrated to a more accurate absolute age scale based on asteroseismic measurements of the mass of red giant stars in NGC6791, and the resulting AMR was fit to compute the look-back time for the beginning of cluster formation in the MW. The fit yields t_GC,i=13.59+0.33-0.32 Gyr for initial cluster formation, and tU=13.79+/-0.34 Gyr for the age of the Universe. This value translates to H0=68.72+3.95-3.49(stat.)+2.65-2.32(sys.) km s-1 Mpc-1, where the systematic error comes from a realistic estimate of the zero point uncertainty on the GC absolute ages derived from stellar models.
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All authors Chiara Zerbinati, Davide Massari, Fernando Aguado-Agelet, Cristiano Fanelli, Massimiliano Matteuzzi, Santi Cassisi, Matteo Monelli, Cristiana Spingola, Carme Gallart, Maurizio Salaris, Roger E. Cohen, Edoardo Ceccarelli, Sara Saracino, Elena Pancino

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

Where Cluster Galaxies Reside and How Strongly They Lens

Isaque Dutra, Priyamvada Natarajan and Cian Roche

The efficiency of galaxy-galaxy strong lensing (GGSL) in clusters depends jointly on the inner mass distributions of member galaxies and their locations within the cluster potential. Observed GGSL probabilities exceed $\Lambda$CDM predictions by nearly an order of magnitude, but the relative roles of internal structure and environment remain unclear. We disentangle these effects by comparing HST strong-lensing clusters with TNG-Cluster analogs at similar lens redshifts, matched by their primary Einstein radius. For each member, we measure its lensing strength in isolation and when embedded in the cluster field. Members in cluster-critical regions are classified as Major or Minor Perturbers depending on whether they strongly lens in isolation; those in subcritical regions are classified as Intrinsic Lenses, Boosted Lenses, or Inert Members according to whether they lens independently, only with environmental assistance, or not at all. Observed clusters contain 33.7% of selected members in cluster-critical regions, compared with 21.6% in TNG-Cluster, while their Major-to-Minor ratios are similar. Outside these regions, observations contain substantially more Intrinsic and Boosted Lenses and fewer Inert Members, with Boosted Lens fractions of 25.8% and 13.5%, respectively. The discrepancy persists at fixed subhalo mass and after including line-of-sight structure. A mass-conserving contraction mimicking core-collapsed self-interacting dark matter largely recovers the conditional lensing fractions but not cluster-critical occupancy. The GGSL discrepancy therefore reflects both insufficient central concentration in simulated members and differences in their locations within the cluster lensing field.
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Astrophysics of Galaxies · Cross-listed from astro-ph.SR

A Spectroscopic Census of Cluster White Dwarfs from DESI, LAMOST, and SDSS

David R. Miller, Jeremy Heyl, Huahui Yan et al. (+2 more)

Gaia has substantially expanded the sample of candidate white dwarfs (WDs) in open clusters, but many remain without spectroscopic characterization. We leverage the increasingly extensive archives of large public spectroscopic surveys to identify 62 candidate cluster WDs with available spectra from DESI, LAMOST, and SDSS. After discarding sources with very low S/N and unreliable host clusters, 44 candidates remain, including 37 non-magnetic DA WDs, of which 15 had not previously been characterized in the literature for cluster studies. We find that nine are consistent with single-star origins in their proposed host clusters, increasing the combined cluster DA initial–final mass relation (IFMR) sample to 132 WDs. All lie within $2\sigma$ of the best-fit IFMR from the most comprehensive recent cluster WD sample, suggesting these additions do not require recalibrating the empirical IFMR. One is a likely Hyades tidal-tail WD, providing further evidence that dynamical dispersal helps explain the long-standing WD deficit in the nearest cluster. We further compare WDs with spectra from multiple surveys. Among seven Praesepe WDs observed by both DESI and SDSS, DESI gives higher WD masses in six cases, with a mean difference of $0.067\,\mathrm{M}_\odot$, while the inferred progenitor masses differ by as much as $0.459\,\mathrm{M}_\odot$. More broadly, nine of ten single-star cluster DAs with DESI spectra lie above the empirical IFMR, with a mean final-mass residual of $0.06\pm0.04\,\mathrm{M}_\odot$. These results show that survey-dependent differences can strongly affect cluster WD parameters, and should be considered when combining heterogeneous spectroscopy in empirical IFMR studies.
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All authors David R. Miller, Jeremy Heyl, Huahui Yan, Chengyuan Li, Pier-Emmanuel Tremblay

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

OGLE-2016-BLG-0523: A Low-mass Brown Dwarf or super-Jupiter in a $>100$ au Orbit

Hongjing Yang, Weicheng Zang, Yoon-Hyun Ryu et al. (+37 more)

To search for very wide-orbit binary-lens events, we cross-match microlensing events detected by OGLE-IV and KMTNet between 2011 and 2024. After removing contaminants from variable stars, we identify OGLE-2016-BLG-0523 as a microlensing event showing two short-lived bumps in its light curve, with the two separated by 8.36 yr. We investigate three scenarios to explain the two bumps, including a binary-lens single-source (2L1S), a single-lens binary-source (1L2S), and two unrelated single-lens single-source events (2$\times$1L1S). The 1L2S interpretation is excluded due to its poorer fit to the data, while the 2$\times$1L1S scenario is disfavored by the low event rate, unphysical total source flux, and unphysical color for one of the two putative sources. For the surviving 2L1S interpretation, the Einstein timescales of the two bumps are $8.343 \pm 0.076$ days and $3.231 \pm 0.047$ days, respectively, implying a binary mass ratio of $q = 0.15$. A Bayesian analysis indicates that the primary lens is most likely a low-mass M dwarf, while the companion is probably a low-mass brown dwarf or super-Jupiter. The inferred projected separation is about 450 au, making the companion the widest low-mass object discovered via microlensing to date. Our discovery highlights both the promise and challenges of identifying very wide, low-mass companions through microlensing. Although upcoming facilities such as Roman and Earth 2.0 space telescopes will improve sensitivity to such events, overcoming degeneracies and distinguishing them from variable phenomena will remain essential for building a robust statistical sample.
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All authors Hongjing Yang, Weicheng Zang, Yoon-Hyun Ryu, Andrzej Udalski, Yuchen Tang, Michael D. Albrow, Sun-Ju Chung, Andrew Gould, Cheongho Han, Kyu-Ha Hwang, Youn Kil Jung, In-Gu Shin, Yossi Shvartzvald, Jennifer C. Yee, Sang-Mok Cha, Dong-Jin Kim, Hyoun-Woo Kim, Seung-Lee Kim, Chung-Uk Lee, Dong-Joo Lee, Yongseok Lee, Byeong-Gon Park, Richard W. Pogge, Przemek Mróz, Michał K. Szymański, Jan Skowron, Radoslaw Poleski, Igor Soszyński, Paweł Pietrukowicz, Szymon Kozłowski, Krzysztof A. Rybicki, Patryk Iwanek, Krzysztof Ulaczyk, Marcin Wrona, Mariusz Gromadzki, Mateusz J. Mróz, Jiyuan Zhang, Shude Mao, Hongyu Li, Qiyue Qian

Astrophysics of Galaxies

A Comprehensive JWST Slitless Spectroscopic Census of $\sim$12,000 Emission-Line Galaxies at Redshift $0\sim9$ in COSMOS

Shuqi Fu, Zijian Zhang, Danyang Jiang et al. (+5 more)

Emission-line galaxies provide key diagnostics of star formation, chemical enrichment, and AGN activity across cosmic time. We present a systematic census of emission-line sources using JWST/NIRCam wide-field slitless spectroscopy (WFSS) from the COSMOS-3D program, which covers a large contiguous area of 0.33 deg$^2$ and provides F444W grism spectroscopy over $3.9$–$5.1\ \mu$m. By combining slitless spectroscopy with deep multi-band imaging data, we construct a homogeneous spectroscopic sample of 12,275 objects at redshift 0–9. The typical $3\sigma$ line-flux limit reaches $3.2\times10^{-18}\ {\rm erg\ s^{-1}\ cm^{-2}}$. To address source confusion inherent to slitless spectroscopy, we develop a multi-step identification framework that combines information from spectra, images, spectral energy distributions, and spatial distributions. We introduce convolutional neural network and large language model to emulate the human identification process and improve efficiency. The resulting catalog provides spectroscopic redshifts, emission-line measurements, and derived physical properties for all sources. The F444W WFSS enables the detection of multiple emission lines, including primarily [O III], H$\alpha$, He I $\lambda10830$, [S III] $\lambda\lambda9531,9069$, Pa$\beta$, Pa$\alpha$, Br$\beta$, PAH, Br$\alpha$, allowing a continuous census of galaxies across cosmic time. We construct composite spectra in several redshift bins and detect a variety of faint spectral features that are difficult to identify in individual spectra, including higher-order hydrogen recombination lines, CO absorption bands, and [Fe II] lines. This catalog provides a key reference dataset for studies of galaxy evolution and AGN activity, and demonstrates the power of WFSS for constructing large, unbiased spectroscopic samples over wide areas. The full catalog will be publicly available online upon publication.
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All authors Shuqi Fu, Zijian Zhang, Danyang Jiang, Jie Chen, Linhua Jiang, Chenxi Bao, Yihe Wang, Ronaldo Laishram