arXiv subjects

Daniel R. Weisz

Publications and source records attributed to Daniel R. Weisz.

At least 19 recordsLinked to original sources

arXiv2026

A census of massive eclipsing binaries in the Whirlpool Galaxy

We present a census of massive eclipsing binary (EB) candidates in the Whirlpool Galaxy (M51), a face-on spiral galaxy at 7.5 Mpc with $Z\sim Z_\odot$. Using 34 epochs of red-optical Hubble Space Telescope (HST) photometry and a single epoch of broadband UV-optical photometry, we identify 173 massive EB candidates ($>5~{\rm M_\odot}$) with orbital periods $P_{\rm orb}$=1-30 days. The sample traces young stellar populations across the spiral arms of M51. Joint light-curve and spectral energy distribution fits for 136 systems yield binaries spanning $T_{\rm eff}=10{,}000$-$50{,}000$ K, $R=7$-$66~{\rm R_\odot}$, and masses of $5$-$120~{\rm M_\odot}$. We use detailed injection-recovery simulations to quantify the survey's completeness and infer intrinsic properties of the massive binary population. At the population level, we infer a close-binary fraction of $f_{\rm close}=27.4\pm7.1\%$ for $2\leq P_{\rm orb}/{\rm d}<20$ and $0.1\leq q\leq1$. Over the same period range, the intrinsic period distribution is consistent with being log-uniform, ${\rm d}N/{\rm d}\log P_{\rm orb}\propto P_{\rm orb}^π$ with $π=0.29\pm0.32$. These demographics broadly match those of massive-star populations in the Milky Way, LMC, and SMC, with tentative evidence for a lower close-binary fraction at lower metallicity. Across the $\sim0.2$-$1.1~Z_\odot$ range spanned by these galaxies, the overall similarities suggest that the formation of close massive binaries depends only weakly on metallicity. Our survey establishes EBs as a powerful tool for measuring massive-binary demographics beyond the Local Group and provides a rich panchromatic census of $\sim$100,000 luminous stars and variables in M51.

astro-ph.SR↗

arXiv2026

Characterising the Globular Cluster Systems of Three Local Group Dwarf Galaxies: NGC6822, NGC147 and NGC185

We present deep HST photometry for 26 globular clusters (GCs) residing in three Local Group dwarf galaxies: the isolated dwarf irregular (dIrr) galaxy, NGC6822, and the M31 dwarf elliptical (dE) satellites, NGC147 and NGC185. From their colour-magnitude diagrams (CMDs), we quantify their red giant branch (RGB) and horizontal branch (HB) morphologies, and employ new empirical relationships to derive measurements of metallicity, reddening and distance. Additionally, we measure sizes and $V$-band magnitudes from their integrated light profiles. We find that the clusters span a range of metallicities, from [Fe/H] $\sim-0.7$ to $\lesssim-2$; however, the three dwarfs have very similar mean GC metallicities ($\sim-1.7$ dex) despite their very different evolutionary histories. In contrast, we find that almost all of NGC6822's GCs exhibit red HB morphologies, whereas those in the two dEs are predominantly blue. We highlight three outlying GCs in NGC6822 that have very low metallicities yet very red HBs; they are also the most extended clusters in our sample, with half-light radii of $\sim 13-17$pc. If these clusters are young, their origin is difficult to explain given their very remote locations, and metallicities which are significantly lower than those of the old and intermediate-age stars in NGC6822. These three clusters are strikingly similar to several GCs linked to substructure in the outer halo of M31, suggesting either the recent accretion of an NGC6822-like dwarf by M31, or that both M31 and NGC6822 have recently accreted a similar low-mass system. Additionally, we find compelling evidence that another NGC6822 cluster, SC7, is tidally distorted.

astro-ph.GA↗

arXiv2026

Probing the IMF in the Early Universe -- Direct measurements in the Boötes I UFD with JWST/NIRCam

The dependence of the stellar initial mass function (IMF) on star-formation environment, particularly at low metallicities and high redshifts, remains poorly constrained. Ultra-faint dwarf galaxies (UFDs) are local fossils of high-redshift galaxies hosting old, metal-poor populations, and their resolved stellar populations provide unique pathways to constrain the sub-solar IMF. We investigate the low-mass IMF in the Bo{ö}tes I (Boo I) UFD with JWST/NIRCam, leveraging its capability to resolve over 10,000 stars reaching $\lesssim$0.15\msun, obtaining one of the largest, deepest resolved stellar samples for UFDs. We explore three different functional forms of the IMF with machine learning and statistical techniques, combining forward modeling of synthetic color-magnitude diagrams with simulation-based inference. We find that a single power-law IMF provides a poorer description of the observed luminosity function and yields a slope inconsistent with the canonical Salpeter IMF. Our best-fit broken power-law and lognormal IMF parameters are consistent with the Milky Way within 68\% confidence level, providing evidence that star formation at metallicities as low as $\mathrm{[Fe/H]}\approx-2.4$ follows a similar IMF as in the Milky Way. By treating Boo I as a local relic analogous to a high-redshift galaxy with a stellar mass of $\lesssim10^5\msun$ at $z\gtrsim6$, our results provide evidence for the universality of the IMF across both local and high-redshift environments.

astro-ph.GA↗

arXiv2026

Hidden mass in early galaxies revealed by bottom-heavy initial mass functions

James Webb Space Telescope (JWST) observations have revealed that massive galaxies formed and evolved faster than predicted by galaxy formation models, with many having already assembled a large mass in stars approximately 12 billion years ago. However, masses of distant galaxies are uncertain, as they assume a distribution of stellar birth masses (the initial mass function (IMF)) similar to that in the Milky Way. Specifically, the contribution from low-mass stars, which make up the bulk of stellar mass, is not directly observed, but inferred based on an extrapolation of the Milky Way IMF. Here, we provide robust constraints on the low-mass IMF beyond the local Universe from full-spectrum models. Using ultra-deep spectra of nine massive quiescent galaxies at redshift $z$ $\approx0.7$ from the JWST Initial Mass Function of Early Red NIRSpec Objects program, extended to bluer wavelengths with deep Very Large Telescope Large Early Galaxy Astrophysics Census spectra, we find that the most massive galaxies have excess low-mass stars. Remarkably, our oldest galaxy (formation redshift $z_{\rm form} > 5$) has the most bottom-heavy IMF. This galaxy may be a descendant of JWST's 'impossibly early' galaxies, implying that the latter may have had similarly bottom-heavy IMFs increasing their masses by a factor of approximately $4\pm1$. Our findings may thus amplify the tension with galaxy formation models.

astro-ph.GA↗

arXiv2026

The Star Formation History of WLM from Asymptotic Giant Branch Stars and The Discovery of a Candidate Accreted System in its Outer Disk

We measure the star formation history (SFH) of Local Group dwarf galaxy WLM using wide-area ($\sim4$ half-light radii) ground-based near-infrared (NIR) imaging of bright ($M_{J}<-4.9$ mag) asymptotic giant branch (AGB) stars. From our NIR color-magnitude diagram (CMD) of 825 stars, we find that our recovered SFH is in excellent agreement with literature SFHs of WLM measured from much deeper CMDs ($M_{F090W}\sim+4.3$ mag) based on JWST imaging. We find good agreement in the qualitative shape of the SFHs as well as quantitative metrics such as the timescales for which 50% and 90% of the stellar mass formed with $τ_{50,{\rm AGB}}=5.16_{-0.50}^{+2.07}$ Gyr ago and $τ_{90,{\rm AGB}}=1.33_{-0.09}^{+0.11}$ Gyr ago versus $τ_{50,{\rm JWST}}=5.94_{-0.31}^{+0.37}$ Gyr ago and $τ_{90, {\rm JWST}}=1.55_{-0.13}^{+0.03}$ Gyr ago. The coarser precision of the AGB star-based values is driven by the low number of AGB stars. We derive an age-metallicity relation (AMR) from the AGB star CMD fitting that is similar to the JWST-based AMR and is consistent with other reported metallicities in WLM (i.e., spectroscopy, RR Lyrae). From our wide-area AGB star map and SFH, we identify a stellar over-density ($M_*\sim2.0\times10^6 M_{\odot}$, $r_h\sim340$ pc) in WLM's northwestern outer disk. Despite WLM having long been considered an isolated galaxy, the mass, size, and age of this over-density are highly suggestive of an accreted dwarf galaxy. Overall, our findings illustrate the power of NIR observations of AGB stars for efficiently and accurately measuring SFHs and for identifying and characterizing substructures in nearby galaxies.

astro-ph.GA↗

arXiv2026

The Star Formation History and Evolution of the Ultra-Diffuse M81 Satellite F8D1

We present deep HST imaging of one of the nearest ultra-diffuse galaxies (UDGs) outside of the Local Group: F8D1, a satellite of M81 known to be tidally disrupting. UDGs are an enigmatic and diverse population, with evolutionary pathways ranging from tidal processing to bursty feedback and high initial angular momentum. To determine F8D1's evolutionary drivers, we resolve stars in F8D1's central $\sim$1 kpc and in a parallel field $\sim$6 kpc along its major axis to deep photometric limits, reaching below the Red Clump. We also image eight shallower fields along F8D1's major and minor axes. We calculate the star formation history (SFH) in the two deep fields, finding that while currently quiescent, both regions experienced a substantial burst $\sim$2 Gyr ago and a smaller burst $\sim$500 Myr ago, which likely formed F8D1's nuclear star cluster. In the shallow fields, using the ratio of evolved Asymptotic Giant Branch and Red Giant Branch stars out to $\sim$13 kpc along F8D1's known stellar stream, we confirm that F8D1 was globally star-forming until at least $\sim$2 Gyr ago. We estimate a total progenitor stellar mass, including the stream, of $\sim$1.3$\times$10$^8 M_{\odot}$, with an average [M/H] $\sim$ $-$0.8. We compare F8D1's properties to those of Local Group galaxies with similar initial stellar mass. We find that F8D1 is consistent with a progenitor star-forming galaxy similar to NGC 6822 that is in the midst of a transition to a Sagittarius-like system. Notably, this evolutionary sequence can be accomplished through tidal processing alone in galaxies that have experienced sufficiently bursty feedback to have created cored profiles.

astro-ph.GA↗

arXiv2026

It's Not Just Star Formation: A trend of low dark matter densities in the Andromeda dwarf galaxy system

Dynamical mass modeling of Andromeda (M31) dwarf spheroidal (dSph) galaxies has revealed a growing trend of lower central dark matter (DM) densities than predicted by pure DM structure formation in Lambda Cold Dark Matter ($Λ$CDM) cosmology simulations and lower than most Milky Way (MW) satellites. So far, however, only four of the 35 confirmed M31 dSphs have been successfully mass modeled. In this second paper of a series, we aim to better understand growing Local Group (LG) dSph patterns by mass modeling seven more M31 dSphs: Andromeda I, III, V, VII, IX, XXXI, and XXXII. We update the kinematics of each dwarf and estimate their central dark matter densities at 150 pc using the dynamical Jeans modeling tool, GravSphere. We also update their DM halo mass, $M_{\rm{200}}$, via abundance matching. We find Andromeda III and V to have central DM densities in line with $Λ$CDM expectations, resembling dSphs around the Milky Way. The remaining five dwarfs have anomalously low central densities, continuing a growing trend seen for M31 satellites. We investigate each dwarf's star formation history and find that star formation-induced `DM heating' is disfavored as the sole explanation of these lower central densities. We consider the effect of tides and halo concentration scatter on these systems and predict that they should be on more plunging orbits than their denser counterparts. If this prediction is misaligned with the data, it could necessitate new physics beyond the Standard Cosmological Model.

astro-ph.GA↗

arXiv2026

Clues to inside-out quenching in quiescent galaxies at $1.2\lesssim z\lesssim2.2$: Age, Fe-, and Mg-abundance gradients from JWST-SUSPENSE

[Abridged] Spatially resolved stellar populations of massive quiescent galaxies at cosmic noon provide powerful insights into quenching and assembly mechanisms. Previous photometric studies have revealed that the cores of these galaxies are redder than their outskirts. However, spectroscopy is needed to break the age-metallicity degeneracy and uncover the driver of colour gradients. We derive age and elemental abundance gradients for eight distant ($1.2 \lesssim z \lesssim 2.2$), massive ($10.3\lesssim\log({\rm M}_*/{\rm M}_\odot)\lesssim 11.1$) quiescent galaxies by fitting full-spectrum models to ultra-deep NIRSpec-MSA spectroscopy from the JWST-SUSPENSE survey. We find that these galaxies have negative age and flat [Fe/H] gradients, and tentative indications of positive [Mg/H] and [Mg/Fe] gradients. These results suggest that galaxy cores are older and perhaps also Mg deficient compared to galaxy outskirts. The age gradients may indicate inside-out quenching, while Mg-deficient cores could suggest rapid gas expulsion as the central quenching mechanism. Thus, galaxy cores may have formed faster and quenched more efficiently than their outskirts. However, our [Fe/H] and [Mg/Fe] gradients are still puzzling, and further investigation is required to understand the nature of [Mg/H] gradients in massive galaxies at these redshifts. Our results contrast with those of lower-$z$ studies, which find flat age and [Mg/Fe] gradients and negative metallicity gradients. Additionally, we find a positive trend between age gradients and rotational support and marginal trends between [Fe/H] gradients and velocity dispersions and ages. We discuss our findings in the context of galaxy growth scenarios, including minor mergers and progenitor bias. With this work, we present the first stellar population gradients from NIRSpec-MSA spectroscopy in the current largest sample of distant quiescent galaxies.

astro-ph.GA↗

arXiv2026

The Panchromatic Hubble Andromeda Southern Treasury (PHAST). II. The Spatially Resolved Recent Star Formation History in M31

We use Hubble Space Telescope optical imaging from the Panchromatic Hubble Andromeda Southern Treasury (PHAST) to measure the spatially resolved recent star formation history (SFH) across the southern disk of M31. We fit color-magnitude diagrams (CMDs) of over 6500 individual 0.01 kpc$^2$ regions to measure SFHs over the last $\sim$500 Myr. The resulting maps show coherent structure that traces the ringed morphology of the disk. We find a clear global decline in the recent SFR, with a pronounced drop in the last $\sim$40 Myr that is most evident in the region closest to M32. Combining PHAST and PHAT measurements, we now cover two thirds of M31's star-forming disk with homogeneous SFHs, yielding the highest-resolution spatially resolved SFHs of M31. Inside the joint footprint, we measure mean SFRs of $0.445 \pm0.006$ M$_\odot$ yr$^{-1}$ over the last 100 Myr and $0.285 \pm 0.014$ M$_\odot$ yr$^{-1}$ over the last 20 Myr, implying total disk SFRs of $\sim$0.67 and $\sim$0.43 M$_\odot$ yr$^{-1}$, respectively. The observed decline is interpreted as the late stage of a multi-Gyr wind-down from a previously more active state. Because recent star formation in M31 is concentrated primarily in the rings, the global decline is driven mainly by decreasing activity within those features. We also compare the CMD-based SFR surface densities to those inferred from FUV+24 $μ$m prescriptions and find that the FUV-based calibration underestimates the CMD-based 100 Myr average by a factor of $\sim$2.1. However, the PHAST SFHs produce a synthetic GALEX FUV image that agrees well with observations, indicating that the CMD-derived SFHs provide an accurate description of recent star formation. The mismatch with the FUV+24 $μ$m estimates underscores that tracers implicitly averaged over $\sim$100 Myr are not reliable when the recent SFR is evolving.

astro-ph.GA↗

arXiv2026

Are Nucleosynthetic Yields Universal? Interpreting the Multi-Elemental Abundances of Quiescent Galaxies over Cosmic Time Using Milky Way Stars

The detailed abundance patterns of quiescent galaxies offer powerful constraints on their formation and evolution. Yet physical insight remains elusive, as nucleosynthetic yields are notoriously uncertain. We introduce a framework that circumvents this problem by using Milky Way abundance trends as empirical proxies for the yields. Applied to quiescent galaxies spanning three redshifts, SDSS ($z\sim0$), LEGA-C ($z\sim0.7$), and JWST/SUSPENSE ($z\sim2$), our approach recovers the $α$- and Fe-peak abundances with a median offset of ~0.05 dex across 14 elements, compared to ~0.23 dex for theoretical yields. The largest discrepancies arise in N, Sr, Ba, and (at $z\sim2$) C, all of which depend on AGB enrichment, a channel we do not explicitly model. We explore the impact of a top-heavy IMF on our predictions and find that it can shift the IMF-averaged core-collapse supernova yields by ~0.05-0.2 dex in a direction that reduces the overall residuals. Surprisingly, the predictions succeed even without modeling the full chemical-evolution history of a galaxy; just Mg and Fe, which trace the relative contributions of core-collapse and Type Ia supernovae, suffice to predict $α$- and Fe-peak elements. The success of the empirical yields, previously demonstrated in dwarf galaxies and the Milky Way disk, and now extended to massive quiescent galaxies, suggests that $α$- and Fe-peak nucleosynthetic yields are largely universal. This lack of complexity makes galaxy abundance patterns highly predictable. Embedding these empirical yields in SPS models will improve inferences on stellar population properties and star formation histories. Moreover, incorporating them into cosmological simulations will produce more observationally motivated predictions.

astro-ph.GA↗

arXiv2026

Unveiling Massive Main-Sequence Stars in Sextans A through Panchromatic Photometry

We present a study of the metal-poor (~6% Z_sun) massive (>8 M_sun) main-sequence star population in the star-forming dwarf galaxy Sextans A. By modeling near-UV to near-IR photometry of individual stars using the Bayesian Extinction and Stellar Tool (BEAST) we infer stellar parameters such as effective temperature, luminosity, and initial mass. We identify 867 massive main-sequence star candidates (present-day mass >8 M_sun and surface gravity >3.7 dex [cgs]) with a plausible spectral energy distribution (SED) fit, 500 of which show a probable SED fit. Comparisons to spectral types of existing observed spectra are consistent with the BEAST-derived stellar parameters, with most discrepancies explained. We identify 292 OBe star candidates through IR photometric signatures and find lower-limit OBe fractions of 15% for M > 8 M_sun, 23% for M > 15 M_sun, and 17% for M > 20 M_sun. We find 57 OB associations and that 24-28% of massive stars are isolated (distance to nearest massive star >28 pc). We discuss six likely runaway candidates (suggested velocities of ~ 50-340 km/s) not clearly associated with any major star-forming complexes. Lastly, we predict Lyman continuum (LyC) escape fractions of f_esc=0.27-0.76 across the star-forming regions and a global value of 0.35-0.71 by assuming low overall extinction and a range of porous geometries, indicating efficient leakage of ionizing photons. Future spectroscopic follow-up and resolved ISM studies will refine these constraints and solidify Sextans A as a benchmark for studying massive-star evolution and feedback at extremely low metallicity.

astro-ph.SR↗

arXiv2026

The JWST Resolved Stellar Populations Early Release Science Program. IX. The RR Lyrae Population in WLM with HST and JWST

RR Lyrae stars are a common, dependable Population II distance indicator, and provide an independent tracer of early star formation. Here, we utilize archival HST/ACS and JWST/NIRCam observations of the nearby dwarf star-forming galaxy WLM to study RR Lyrae in JWST filters. We independently identify RR Lyrae in HST and JWST imaging in order to evaluate JWST's efficacy at characterizing RR Lyrae in the near-IR. We use an MCMC template-fitting technique to obtain periods, amplitudes, and mean magnitudes from the RR Lyrae time-series data. The spatially overlapping HST and JWST observations allow us to directly compare the same sources observed with the instruments, and calibrate the NIRCam F090W and F150W RR Lyrae period-Wesenheit-metallicity (PWZ) relation to the Gaia-consistent HST PWZ. We additionally assess the epoch-to-epoch consistency of NIRCam photometry, and find evidence of burn-in. We conclude that the zero-point offset is negligible compared to the uncertainties from the template fitting. We conduct an MCMC fit of the PWZ with both HST and JWST data. Our results are three-fold. First, we find that we can reliably identify RR Lyrae in NIRCam data, but light-curve template fitting proves difficult on short-baseline observations. Second, the HST PWZ fit yields a distance modulus to WLM of $μ= 24.85\pm0.05$ ($0.93\pm0.02$ Mpc). This is closer than previous measurements, primarily attributed to consistency with the Gaia scale. Lastly, although the JWST PWZ fit has large uncertainties and a poorly-constrained slope, it represents a first-of-its-kind PWZ calibration in NIRCam filters.

astro-ph.GA↗

arXiv2026

A Path to an All-Sky Survey with Roman

A deep, space-based, all-sky near-infrared survey carried out with the Nancy Grace Roman Space Telescope would constitute a foundational astronomical infrastructure for decades to come. In this white paper, we present a concrete and feasible path to imaging the entire sky at $\sim0.1''$ resolution, beginning with high-impact fields in Cycle 1 and scaling to ultra-wide coverage within the nominal mission. This first-epoch survey will reach $\mathrm{H}\sim25.5$ AB mag (5$σ$) and maximize synergies with contemporaneous observatories, while preserving substantial time for other ambitious Roman programs. We outline representative scheduling scenarios and an example Cycle 1 program that triples early Roman-LSST overlap and delivers high-value community data products such as LSST forced photometry, joint \textit{Gaia}-Roman astrometry, and catalogs of Galactic substructure, stong lenses, and other rare systems. The Cycle 1 program will lay the foundation for an eventual all-sky survey, while also delivering high-impact early science. We invite broad community participation in shaping and carrying out both the initial program and the long-term vision of an all-sky Roman survey.

astro-ph.IM↗

arXiv2026

Dwarf Galaxy Number Counts within 25 Mpc: Predictions from Local Group Analogues in TNG50

The modern generation of wide-field galaxy surveys, such as LSST, Euclid and Roman, will enable studies of dwarf galaxies $(10^6 \leq M_\ast / M_\odot \leq 10^9)$ beyond the Local Group (LG) in unprecedented detail. Improved theoretical understanding of this population is necessary to guide these observations, since predictions in this regime are generally limited to specific environments like the LG. We present predictions for the population of dwarf galaxies from the TNG50 run of the IllustrisTNG suite of cosmological hydrodynamical simulations, focusing on the environments within $1 < D / \mathrm{Mpc} < 25$ of LG analogues at $z = 0$. In the simulated sample, there are $\sim 1,000$ and $\sim 12,000$ dwarf galaxies within $10$ and $25$ Mpc, respectively. We compare our results with the 50 Mpc Galaxy Catalog and estimate that current observations are highly incomplete at low masses: for $10^6 \leq M_\ast / M_\odot \leq 10^7$ $(-13 \lesssim M_r \lesssim -10)$, we find completeness fractions of $\sim 23 \%$ within $10$ Mpc and $\sim 4 \%$ within $25$ Mpc. The simulated galaxies below the completeness limits of the observations exist in a range of environments, with notable populations of field dwarfs at all distances and satellites around centrals with masses $10^8 \lesssim M_\ast / M_\odot \lesssim 10^{11}$ within $10-25$ Mpc. We find that there are $\sim 8$ times more quiescent dwarf galaxies in the TNG50 sample than are currently cataloged. Our results suggest that upcoming observations should uncover a substantial population of dwarf galaxies, and that $\gtrsim 15 \%$ of these will be red, currently quenched galaxies in the field.

astro-ph.GA↗

arXiv2025

Measuring Star Formation Histories from Asymptotic Giant Branch Stars I: A Demonstration in M31

We demonstrate how near-infrared (NIR) imaging of resolved luminous asymptotic giant branch (AGB) stars can be used to measure well-constrained star formation histories (SFHs) across cosmic time. Using UKIRT $J$ and $K$-band imaging of M31, we first show excellent agreement over the past $\sim8$ Gyr between the PHAT SFH of M31's outer disk derived from a deep optical color-magnitude diagram (CMD; $\sim3.3\times10^{7}$ stars with $M_{\rm F814W} \lesssim +2$), and our spatially-matched SFH based only on modeling AGB stars on a NIR CMD ($\sim7.7\times10^{3}$ stars with $M_{\rm J} \lesssim -6$). We find that only $\sim1000$ AGB stars are needed for reliable SFH recovery, owing to their excellent age sensitivity in the NIR. We then measure the spatially-resolved SFH of M31's inner stellar halo ($D_{\rm M31, projected} \sim20-30$ kpc) using $\sim10^4$ AGB stars. We find: (i) a dominant burst of star formation across M31's stellar halo $3-5$ Gyr ago and lower level, spatially distributed star formation $\sim1-3$ Gyr ago; (ii) $M_{\star}\approx3_{-1}^{+5}\times10^9 M_{\odot}$ formed over the past $\sim8$ Gyr. We discuss some caveats and the enormous potential of resolved AGB stars in the NIR for measuring SFHs back to ancient epochs ($\sim14$ Gyr ago) in galaxies to large distances ($D\gtrsim20$ Mpc) with JWST, Roman, and Euclid.

astro-ph.GA↗

arXiv2025

Wide binaries in an ultra-faint dwarf galaxy: discovery, population modeling, and a nail in the coffin of primordial black hole dark matter

We report the discovery and characterization of a wide binary population in the ultrafaint dwarf galaxy Boötes I using deep JWST/NIRCam imaging. Our sample consists of 52 candidate binaries with projected separations of 7,000 - 16,000 au and stellar masses from near the hydrogen-burning limit to the main-sequence turnoff ($\sim0.1$ - $0.8~{\rm M_\odot}$). By forward-modeling selection biases and chance alignments, we find that $1.25\pm0.25\%$ of Boötes I stars are members of wide binaries with separations beyond 5,000 au. This fraction, along with the distributions of separations and mass ratios, matches that in the Solar neighborhood, suggesting that wide binary formation is largely insensitive to metallicity, even down to [Fe/H] $\approx -2.5$. The observed truncation in the separation distribution near 16,000 au is well explained by stellar flyby disruptions. We also discuss how the binaries can be used to constrain the galaxy's dark matter properties. We show that our detection places new limits on primordial black hole dark matter, finding that compact objects with $M \gtrsim 5~{\rm M_\odot}$ cannot constitute more than $\sim1\%$ of the dark matter content. In contrast to previous work, we find that wide binaries are unlikely to provide robust constraints on the dark matter profile of ultrafaint galaxies given the uncertainties in the initial binary population, flyby disruptions, and contamination from chance alignments. These findings represent the most robust detection of wide binaries in an external galaxy to date, opening a new avenue for studying binary star formation and survival in extreme environments.

astro-ph.GA↗

arXiv2025

Fast Rotators at Cosmic Noon: Stellar Kinematics for 15 Quiescent Galaxies from JWST-SUSPENSE

We present spatially-resolved stellar kinematics of 15 massive ($M_*=10^{10.5-11.5}M_{\odot}$) quiescent galaxies at $z\sim1.2-2.3$ from the JWST-SUSPENSE program. This is the largest sample of spatially-resolved kinematic measurements of quiescent galaxies at cosmic noon to date. Our measurements are derived from ultra-deep NIRSpec/MSA stellar absorption line spectra, using a forward modelling approach that accounts for optics, source morphology, positioning, and data reduction effects. 10 out of 15 galaxies are orientated such that we can measure rotational support. Remarkably, all 10 galaxies show significant rotation ($V_{r_e}=117-345$km/s, $σ_0 = 180-387$km/s), and are classified as "fast rotators" from their spin parameter. The remaining galaxies are too misaligned with respect to the slit to constrain their rotational velocities. The widespread rotational support in our sample indicates that the process responsible for quenching star formation in early massive galaxies did not destroy rotating disc structures. When combined with other quiescent galaxy samples at $z\sim0.5-2.5$, we find a trend between rotational support and age, with younger quiescent galaxies being more rotationally supported. This age trend has also been found at $z\sim0$, and likely explains why our high-redshift galaxies show more rotational support compared to massive ETGs at $z\sim0$, which are, on average, older. Our kinematic modelling also enables us to calculate dynamical masses. These dynamical masses greatly exceed the stellar masses for our sample (median $M_{\text{dyn}}/M_*=2.7$); they even allow for the bottom-heavy IMF found in the cores of low-$z$ massive ellipticals. Altogether, our results support a scenario in which distant quiescent galaxies evolve into nearby massive ETGs, gradually building up their outskirts and simultaneously losing rotation, due to a series of (mostly minor) mergers.

astro-ph.GA↗

arXiv2025

The Karl G. Jansky Very Large Array Local Group L-band Survey (LGLBS)

We present the Local Group L-Band Survey (LGLBS), a Karl G. Jansky Very Large Array (VLA) survey producing the highest quality 21-cm and 1-2 GHz radio continuum images to date for the six VLA-accessible, star-forming, Local Group galaxies. Leveraging the VLA's spectral multiplexing power, we simultaneously survey the 21-cm line at high 0.4 km/s velocity resolution, the 1-2 GHz polarized continuum, and four OH lines. For the massive spiral M31, the dwarf spiral M33, and the dwarf irregular galaxies NGC6822, IC10, IC1613, and the Wolf-Lundmark-Melotte Galaxy (WLM), we use all four VLA configurations and the Green Bank Telescope to reach angular resolutions of $< 5''$ ($10{-}20$~pc) for the 21-cm line with $<10^{20}$~cm$^{-2}$ column density sensitivity, and even sharper views ($< 2''$; $5{-}10$~pc) of the continuum. Targeting these nearby galaxies ($D\lesssim1$ Mpc) reveals a sharp, resolved view of the atomic gas, including 21-cm absorption, and continuum emission from supernova remnants and HII regions. These datasets can be used to test theories of the abundance and formation of cold clouds, the driving and dissipation of interstellar turbulence, and the impact of feedback from massive stars and supernovae. Here, we describe the survey design and execution, scientific motivation, data processing, and quality assurance. We provide a first look at and publicly release the wide-field 21-cm HI data products for M31, M33, and four dwarf irregular targets in the survey, which represent some of the highest physical resolution 21-cm observations of any external galaxies beyond the LMC and SMC.

astro-ph.GA↗