arXiv subjects

Evan N. Kirby

Publications and source records attributed to Evan N. Kirby.

At least 19 recordsLinked to original sources

arXiv2026

Galactic Archaeology with the Subaru `Ōnohi`ula Prime Focus Spectrograph Strategic Program

The recently commissioned Subaru `Ōnohi`ula Prime Focus Spectrograph (PFS) will obtain spectra from nearly 2,400 fibers that cover 1.24 square degrees. The 360 night Subaru Strategic Program for PFS is dedicating approximately one-third of its allocation (130 nights) to study the structure and evolution of galaxies in the Local Group. This Galactic Archaeological survey has three pillars. (1) We will determine whether the mass density profiles of dwarf galaxies are consistent with cusps, as expected for cold dark matter, or cores, as expected from alternative dark matter theories or baryonic feedback. We will deduce the density profiles as a function of radius from modeling of the full line-of-sight velocity and abundance distributions for six dwarf galaxies. Our total sample will consist of 18,000 member stars to beyond the nominal tidal radius of each system. (2) From measurements of the [alpha/Fe] abundance ratio, we will learn the difference in assembly history of the two most massive galaxies in the Local Group: M31 and the Milky Way. We will observe 30,000 member stars over 45 square degrees of M31's halo and outer disk. (3) We will uncover how the most fragile (outer) part of the Milky Way responded to accretion events both in the distant past (such as Gaia-Sausage Enceladus) and in more recent history (such as the Sagittarius dwarf spheroidal galaxy). To support this study, PFS will provide velocities and metallicities--from which, in combination with photometry, we will deduce ages--for tens of thousands of main-sequence stars out to a Galactocentric distance of ~30 kpc.

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arXiv2026

The Treasury of Extremely Metal-Poor O Stars

The Treasury of Extremely Metal-Poor O Stars (TEMPOS) is a Hubble Space Telescope survey of hot and massive O-type stars in nearby, low-metallicity galaxies ($\lesssim$20% of the solar metallicity, $Z_\odot$). Understanding massive-star physics in this regime is essential to interpret observations of metal-poor galaxies, including both low-mass dwarf galaxies and chemically unevolved galaxies in the early Universe. Yet, few far-ultraviolet (FUV) spectra of O stars of sufficient quality to characterize their fundamental properties and stellar winds exist below 20% $Z_\odot$, and heterogeneous observation design and incomplete coverage of parameter space pose significant barriers to progress. To remedy this, TEMPOS obtained new Cosmic Origins Spectrograph (COS) FUV spectra of 12 very metal-poor O stars, building upon archival data to assemble a spectroscopic atlas of 29 homogeneously observed stars that efficiently samples a wide range of spectral types and luminosity classes. Here, we describe the motivation, sample selection, and observation design for TEMPOS and present the first data release of reduced and coadded COS spectra. We then present initial results on the empirical properties of FUV O-star spectra below 20% $Z_\odot$, including radial velocities, equivalent widths of photospheric lines, and terminal wind velocities ($v_\infty$). We show that $v_\infty$ correlates with host galaxy metallicity across $\sim$5-50% $Z_\odot$ and find tentative evidence of a steeper decline in wind strength below $\sim$10% $Z_\odot$. The combined dataset of FUV spectra and planned releases of photometry and optical spectra from the TEMPOS Treasury program will advance our understanding of both stellar astrophysics and the interstellar medium in the extremely metal-poor regime.

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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.

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arXiv2026

HRMOS: A High-Resolution Multi-Object Spectrograph for the VLT

This White Paper presents the scientific rationale and instrument concept for HRMOS (High-Resolution Multi-Object Spectrograph), a next-generation instrument proposed for the ESO Very Large Telescope within the VLT 2030 roadmap. Current and planned facilities offer either multi-object spectroscopy or ultra-high spectral resolution, but not both. HRMOS fills this gap by combining very high spectral resolution, multi-object capability, and radial-velocity stability, enabling transformative studies in Galactic and extragalactic astrophysics. The baseline design provides a resolving power of R = 80000, radial-velocity precision of 10 m s-1 (goal: 5 m s-1), simultaneous observations of 50-60 targets, and broad optical coverage down to 385 nm. These capabilities enable precise measurements of elemental abundances, isotopic ratios, line profiles, and radial velocities for large stellar samples, including crowded fields, star clusters, the Galactic bulge, and nearby dwarf galaxies. HRMOS will address key questions on the age of the oldest stellar populations through nucleocosmochronology, the formation and survival of planetary systems, the assembly history of the Milky Way and satellites, the origin of the heaviest elements, stellar evolution, and the chemical and dynamical properties of the interstellar and circumgalactic medium. It will bridge large spectroscopic surveys and the next generation of extremely large telescopes, with strong synergies with 4MOST, Gaia, TESS, PLATO, the proposed Haydn mission, and future ELT instruments. Building on VLT/FLAMES heritage, HRMOS represents a strategic investment for European astronomy in the 2030s.

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arXiv2026

Evidence of Supernova Between Formation of Stellar Populations in a Globular Cluster

Globular clusters do not undergo conventional chemical evolution driven by supernova enrichment. Instead, they exhibit unique abundance patterns of the light elements, which cannot be fully explained by any of the proposed enrichment mechanisms. "Normal" stars of low sodium abundances comprise the first population of cluster stars, and "enriched" stars of high sodium abundances, which are found only in globular clusters, comprise the second population. Here we show from a differential line-by-line analysis of stars that span a small range of effective temperature that the globular cluster M92 has higher Fe abundances in second-population (sodium-enhanced) stars than first-population stars. The two populations are well separated in Na, Al, and Fe abundances. The rise in Fe abundance between the first and second stellar populations suggests that M92 was able to retain at least some supernova ejecta, all of which exploded after the first population finished forming. This result provides a lower limit for the time delay between populations.

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arXiv2026

Weak-CN Stars Are Ordinary Cool Red Supergiants

Weak CN absorption near ~8000 A has recently been detected in evolved red supergiants (RSGs) of 5-10 $M_\odot$ across three Local Group galaxies. These weak-CN RSGs sit in a narrow molecular regime: cool enough for CN to be visible in a non-carbon, C/O<1 atmosphere, but warm enough that TiO is not saturated and changes in $T_{\rm eff}$ and in the surface C+N reservoir move CN and TiO in distinct directions. We test this picture with pseudo-continuum equivalent widths (EWs) measured from LMC, M33, and M31 weak-CN and carbon-star coadds, compared at matched resolution to a self-consistent grid of synthetic RSG atmospheres spanning $T_{\rm eff}$, $[α/{\rm Fe}]$, and surface C and N offsets relative to each host's scaled-solar baseline. Ordinary cool-RSG models reproduce the weak-CN coadds across all three hosts, with per-feature residuals at the level of the adopted EW systematic floors. The robust observable is the combined surface abundance $Δ$[C/H]+$Δ$[N/H] rather than each offset individually, because CN forms from the product of available C and N number densities. Mapping $Δ$[C/H]+$Δ$[N/H] to initial rotation through PARSEC v2.0 has modest leverage -- the variable shifts by ~0.07 dex from $ω_i$=0 to $ω_i$=0.6 -- and within this resolution slow-rotation first dredge-up is consistent with LMC and M33, and with M31 once a single-feature CaT 8542 A calibration anchor is allowed. The straightforward resolution of the discovery puzzle is therefore that weak CN is not an exotic carbon-star intermediate but the expected molecular-equilibrium signature of ordinary cool RSGs.

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arXiv2026

It's a matter of time: Empirical Constraints on Supernova Yields and Delay Times from Dwarf Spheroidal Galaxies

The chemical abundances of a stellar population encode information about nucleosynthesis and its astrophysical sites, but this information is confounded by the specific star formation history of the host galaxy. As a result, placing empirical constraints on supernova yields and timing using abundances has been very challenging. We introduce a galactic chemical evolution model DLEIY that uses an observed star formation history and metallicity distribution to reduce these confounding factors. Using a joint statistical model of the dwarf spheroidal galaxies Sculptor and Fornax, simultaneous constraints on population-averaged yields and galactic outflows are achieved with DLEIY, without fixing the absolute scale of nucleosynthetic yields. The Fe yield from core collapse supernovae is consistent with existing theoretical yield models, while the measured Mg yield is a factor of 2-4 higher, corroborating previous suggestions that yield models may under-predict [Mg/Fe]. We also find that the rate of Type Ia supernovae is enhanced by about a factor of 5 relative to field galaxies, and the delay-time distribution goes as $\sim t^{-2}$, a much steeper relationship than that measured from supernova surveys ($\sim t^{-1.1}$). These findings may suggest a metallicity dependence of the Type Ia rate and delay-time distribution.

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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.

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arXiv2026

A Chemodynamical Census of the Milky Way's Ultra-Faint Compact Satellites. I. A First Population-Level Look at the Internal Kinematics and Metallicities of 19 Extremely-Low-Mass Halo Stellar Systems

Deep, wide-area photometric surveys have uncovered a population of compact ($r_{1/2} \approx$ 1-15 pc), extremely-low-mass ($M_* \approx$ 20-4000 $M_{\odot}$) stellar systems in the Milky Way halo that are smaller in size than known ultra-faint dwarf galaxies (UFDs) and substantially fainter than most classical globular clusters (GCs). Very little is known about the nature and origins of this population of "Ultra-Faint Compact Satellites" (UFCSs) owing to a dearth of spectroscopic measurements. Here, we present the first spectroscopic census of these compact systems based on Magellan/IMACS and Keck/DEIMOS observations of 19 individual UFCSs, representing $\sim$2/3 of the known population. We securely measure mean radial velocities for all 19 systems, velocity dispersions for 15 (predominantly upper limits), metallicities for 17, metallicity dispersions for 8, and $\textit{Gaia}$-based mean proper motions for 18. This large new spectroscopic sample provides the first insights into population-level trends for these extreme satellites. We demonstrate that: (1) the UFCSs are kinematically colder, on average, than the UFDs, disfavoring very dense dark matter halos in most cases, (2) the UFCS population is chemically diverse, spanning a factor of $\sim$300 in mean iron abundance ($\rm -3.3 \lesssim [Fe/H] \lesssim -0.8$), with multiple systems falling beneath the "metallicity floor" proposed for GCs, and (3) while some higher-metallicity and/or younger UFCSs are clearly star clusters, the dynamical and/or chemical evidence allows the possibility that up to $\sim$50% of the UFCSs in our sample (9 of 19) may represent the smallest and least-massive galaxies yet discovered.

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arXiv2026

Carbon-Enhanced Metal-Poor Star Candidates in the Milky Way from J-PLUS and S-PLUS

Recent large-scale multi-band photometric surveys now enable elemental-abundance estimates for millions of stars with accuracies approaching those of low- to medium-resolution spectroscopy. Using [Fe/H] and [C/Fe] estimates derived from the Javalambre Photometric Local Universe Survey (J-PLUS) DR3 and the Southern Photometric Local Universe Survey (S-PLUS) DR4, which together cover $\sim$6,200 deg$^2$ of the sky, we identify large numbers of carbon-enhanced metal-poor (CEMP) stars in the Milky Way. After applying data-quality cuts and evolutionary corrections to the carbon-abundance estimates, we construct a combined J/S-PLUS sample of $\sim$6.40 million stars and identify $\sim$104,900 CEMP candidates, roughly twice the number of CEMP candidates identified from Gaia XP spectra by Lucey et al. We photometrically confirm that the absolute carbon abundance $A$(C) separates CEMP stars into two primary groups, CEMP-no and CEMP-$s$ stars, consistent with previous spectroscopic studies. We also recover CEMP morphological Groups I-III in the Yoon-Beers diagram, as well as the recently proposed Group IV, and show that it is statistically distinct even in photometric data. A cumulative frequency analysis confirms that the CEMP fraction increases toward lower metallicity and that CEMP-no stars dominate in the most metal-poor regime. By comparing frequencies with and without Group IV stars, we assess their relation to CEMP-no and CEMP-$s$ stars, and examine CEMP distributions across different Galactic components. The resulting catalog provides a substantial sample for future spectroscopic follow-up, in particular to constrain the likely origin(s) of the Group IV stars.

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arXiv2025

No Observational Evidence for Dark Matter Nor a Large Metallicity Spread in the Extreme Milky Way Satellite Ursa Major III / UNIONS 1

The extremely-low-luminosity, compact Milky Way satellite Ursa Major III / UNIONS 1 (UMaIII/U1; $L_V = 11 \ L_{\odot}$; $a_{1/2} = 3$ pc) was found to have a substantial velocity dispersion at the time of its discovery ($σ_v = 3.7^{+1.4}_{-1.0} \rm \ km \ s^{-1}$), suggesting that it might be an exceptional, highly dark-matter-dominated dwarf galaxy with very few stars. However, significant questions remained about the system's dark matter content and nature as a dwarf galaxy due to the small member sample ($N=11$), possible spectroscopic binaries, and the lack of any metallicity information. Here, we present new spectroscopic observations covering $N=16$ members that both dynamically and chemically test UMaIII/U1's true nature. From higher-precision Keck/DEIMOS spectra, we find a 95% confidence level velocity dispersion limit of $σ_v< 2.3 \rm \ km \ s^{-1}$, with a $\sim$120:1 likelihood ratio now favoring the expected stellar-only dispersion of $σ_* \approx 0.1 \rm \ km \ s^{-1}$ over the original $3.7 \rm \ km \ s^{-1}$ dispersion. There is now no observational evidence for dark matter in the system. From Keck/LRIS spectra targeting the Calcium II K line, we also measure the first metallicities for 12 member stars, finding a mean metallicity of $\rm [Fe/H] = -2.65 \; \pm \, 0.1$ (stat.) $\pm \,0.3$ (zeropoint) with a metallicity dispersion limit of $σ_{\rm [Fe/H]} < 0.35$ dex (at the 95% credible level). Together, these properties are more consistent with UMaIII/U1 being a star cluster, though the dwarf galaxy scenario is not fully ruled out. Under this interpretation, UMaIII/U1 ranks among the faintest and most metal-poor star clusters yet discovered.

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arXiv2025

Machine Learning Techniques to Distinguish Giant Stars from Dwarf Stars Using Only Photometry -- Pushing Redwards

We present our photometric method, which combines Subaru/HSC $NB515$, g, and i band filters to distinguish giant stars in Local Group galaxies from Milky Way dwarf contamination. The $NB515$ filter is a narrow-band filter that covers the MgI+MgH features at $5150$ Å, and is sensitive to stellar surface gravity. Using synthetic photometry derived from large empirical stellar spectral libraries, we model the $NB515$ filter's sensitivity to stellar atmospheric parameters and chemical abundances. Our results demonstrate that the $NB515$ filter effectively separates dwarfs from giants, even for the reddest and coolest M-type stars. To further enhance this separation, we develop machine learning models that improve the classification on the two-color ($g-i$, $NB515-g$) diagram. We apply these models to photometric data from the Fornax dwarf spheroidal galaxy and two fields of M31, successfully identifying red giant branch stars in these galaxies.

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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.

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arXiv2025

The Extended Stellar Distribution in the Outskirts of the Ursa Minor Dwarf Spheroidal Galaxy

We discover an extended distribution of main-sequence (MS) stars along the minor axis of the Ursa Minor (UMi) dwarf spheroidal galaxy (dSph). This study is enabled by deep, wide Subaru/Hyper Suprime-Cam data, reaching photometric uncertainties below 0.1 mag at $g,i \sim 26$ mag. Color-magnitude diagrams along the major and minor axes reveal a clear excess of MS stars beyond the nominal tidal radius along the minor axis. To characterize this structure, we derive radial number density profiles in seven azimuthal directions and fit them with an exponential+power-law function to assess the symmetry of the extended component. The power-law slopes tend to be shallower toward the minor axis, though the symmetry remains inconclusive within 1$σ$ uncertainties. This may indicate that the extended component is preferentially distributed along the minor axis, and could be different from the previously suggested tidal features along the major axis. Comparing with simulations, we find that the fraction of stars beyond five effective radii is consistent with expectations from an intermediate mass ratio merger scenario with a stellar mass ratio around 6:1. While these findings provide new insights into the structural complexity and dynamical history of the UMi dSph, alternative mechanisms such as stellar or supernova feedback have also been proposed for extended stellar halos in dwarfs and cannot be ruled out.

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arXiv2025

Population-Dependent r-process Scatter in the Globular Cluster M15

Multiple populations, defined by correlations between light element abundances, are an almost ubiquitous property of globular clusters. On the other hand, dispersions among the heavy elements are limited to a few rare clusters. In this letter, we present Mg, Y, Ba, La, and Eu measurements for 89 stars in M15 with errors < 0.4 dex from Keck/DEIMOS medium-resolution spectra. We find higher Ba, La, and Eu dispersions in the first generation of stars than in the second generation at a significance of $\ge$2 $σ$. This is evidence for inhomogeneous mixing of gas during the formation of the first generation of stars, which subsequently became well-mixed prior to the formation of the second generation of stars. If the r-process event that caused the abundance dispersions was born with the first population of stars, it must be an r-process site with a short delay time.

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arXiv2025

The Star Formation and Chemical Evolution Histories of Ursa Minor Dwarf Spheroidal Galaxy

We derive the star formation history (SFH) and chemical evolution history (CEH) of the Ursa Minor (UMi) dwarf spheroidal galaxy (dSph). We detect two distinct stellar populations that exist over 6 times half-light radius from its center. The results are obtained by applying a newly developed algorithm to the deep and wide-field photometric dataset taken with Hyper Suprime-Cam on the Subaru Telescope. The algorithm employs the genetic algorithm and the simulated annealing to minimize a $χ^{2}$ value between the observed color-magnitude diagram (CMD) and synthetic CMD generated from the stellar isochrones. The age and metallicity resolutions are set to $0.5$ Gyr and $0.1$ dex, respectively. The accuracy assessment with mock galaxies shows that it returns the peaks of metallicity distributions and star formation period within 1 $σ$ of input value in the case of a single population. In tests with two populations, two distinct metallicity peaks are identified without an offset from the input values, indicating the robustness of this algorithm. The detected two populations in the UMi dSph have the metallicity peaks of [Fe/H] = $-2.2$ and $-2.5$; the metal-rich population started its star formation about 1 Gyr later than the metal-poor one. The SFH of both metal-rich and metal-poor populations varies with distance from the center of the UMi dSph, without any age-gradients. These results suggest that the UMi dSph underwent a complex formation process, contrary to the simple formation history of dwarf galaxies previously thought.

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arXiv2025

$r$-process Abundance Dispersion in the Globular Cluster M5 using Keck Archival Data

We studied $28$ RGB stars in the mildly metal-rich globular cluster M5 ([Fe/H] $= -1.29$) using archival high-resolution spectra from the Keck Observatory archive (KOA) to better understand the $r$-process in globular clusters. Previous studies (M15, M92, and NGC 2298) have shown $r$-process dispersion in varying amounts, hinting at the source of the $r$-process in those clusters. We extend these dispersion studies to the more metal-rich cluster M5 by studying the rare-earth peak, specifically the elements Ba, Nd, and Eu. We separately analyze the different stellar generations, as traced by the abundance of Na and O. Based on the Nd and Eu abundances, we report a tenuous detection of $r$-process dispersion that is dependent on the generation and element. Based on a log-likelihood dispersion study accounting for measurement errors, Nd has an intrinsic first generation abundance spread of $σ_{1G}(\text{Nd}) = 0.15_{-0.07}^{+0.10}$ and an $2σ$ upper limit on the second generation spread of $σ_{2G}(\text{Nd}) < 0.28$. The upper limits on the Eu intrinsic spread are $σ_{1G}(\text{Eu}) < 0.34$ and $σ_{2G}(\text{Eu}) < 0.16$. A potential dispersion implies the cluster gas was inhomogeneously polluted, either due to an event concurrent with the formation of the cluster or due to clouds of disparate composition that coalesced to form the cluster.

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arXiv2025

Estimating Fe and Mg Abundances in the Milky Way Dwarf Galaxies Using Subaru/HSC and DEIMOS

We investigate the chemical abundance distributions of the Fornax, Sculptor, Ursa Minor, and Draco dwarf galaxies using Subaru/HSC photometric data. The HSC dataset, which includes broadband g and i filters and the narrowband NB515 filter, offers sensitivity to iron and magnesium abundances as well as surface gravity, enabling the identification of giant stars and foreground dwarfs. For analysis, we selected a total of 6713 giant candidates using a Random Forest regressor trained on medium-resolution (R ~ 6000) Keck/DEIMOS spectroscopic data. Our analysis reveals the extent of radial metallicity gradients in the galaxies. Such trends, not detectable in earlier studies, are now captured owing to the substantially enlarged sample size and areal coverage provided by the HSC data. These results are also consistent with chemical abundance patterns previously observed in the central regions through spectroscopic studies. Furthermore, we infer that Fornax underwent extended star formation, whereas Sculptor formed both metal-poor and metal-rich stars over a shorter time. Ursa Minor and Draco appear to have experienced brief, intense star formation episodes leading to nearly extinguished star formation. This study underscores the critical role of the expanded HSC dataset in revealing chemical gradients that were previously inaccessible. Future work incorporating additional spectra of metal-poor stars and age-sensitive isochrone modeling will enable more accurate maps of chemical abundance distributions.

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