arXiv subjects

Kristen B. W. McQuinn

Publications and source records attributed to Kristen B. W. McQuinn.

At least 19 recordsLinked to original sources

arXiv2026

JWST Observations of RR Lyrae in Leo P

We analyze co-spatial HST/ACS and JWST/NIRCam time-series photometric observations of RR Lyrae in the low-metallicity dwarf galaxy Leo P. This study provides a new opportunity to explore the properties of and potential for metal-poor RR Lyrae studies with JWST using well-understood relationships from past HST work. We identify 20 RR Lyrae in the HST imaging and 15 RR Lyrae in the JWST imaging. We determine the periods, amplitudes, and mean magnitudes for each of the RR Lyrae. We fit the Period-Wesenheit-Metallicity (PWZ) function to the HST RR Lyrae population, and obtain a Gaia-consistent RR Lyrae-based distance to Leo P of $μ= 26.04\pm0.07$ ($1.61\pm0.06$ Mpc), consistent with existing distance measurements. We determine a JWST-based PWZ using Leo P data along with previous JWST RR Lyrae observations in WLM. The simultaneous fit decreases the mean fractional uncertainty by 31% on the slope and by 11% on the intercept, increasing the constraining power as compared to the existing calibration.

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arXiv2026

Growth of Aromatic Hydrocarbon Dust Particles in the Extremely Metal-poor Galaxy Sextans A

The mid-infrared spectrum of star-forming, high metallicity galaxies is dominated by emission features from aromatic and aliphatic bonds in small carbonaceous dust grains, often referred to as polycyclic aromatic hydrocarbons (PAHs). In metal-poor galaxies, the abundance of PAHs relative to the total dust sharply declines, but the origin of this deficit is unknown. We present JWST observations that detect and resolve emission from PAHs in the 7% Solar metallicity galaxy Sextans A, representing the lowest metallicity detection of PAH emission to date. In contrast to higher metallicity galaxies, the clumps of PAH emission are compact (0.5-1.5$''$ or 3-10 pc), which explains why PAH emission evaded detection by lower resolution instruments. Ratios between the 3.3, 7.7, and 11.3 $μ$m PAH features indicate that the PAH grains in Sextans A are small and neutral, with no evidence of significant processing from radiation fields. These results favor inhibited grain growth over enhanced destruction as the origin of the low PAH abundance in Sextans A. The compact clumps of PAH emission are likely active sites of in-situ PAH growth within a dense, well-shielded phase of the interstellar medium. Our results show that PAHs can form and survive in extremely metal-poor environments common early in the evolution of the Universe.

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arXiv2026

H-alpha Star Formation Rates of the SHIELD Dwarf Galaxies

The Survey of HI in Extremely Low-mass Dwarfs (SHIELD) galaxy sample is an HI-selected catalog of galaxies that occupy the extreme low-mass end of the HI mass function. Our team is carrying out a comprehensive multi-wavelength observational program targeting these gas-rich, star-forming dwarf galaxies. The current paper presents H-alpha narrowband observations of the full SHIELD sample. We detect 55 of the 82 galaxies (67%) with nebular H-alpha emission, and infer sensitive upper limits to the H-alpha fluxes for the 27 non-detections. We derive H-alpha luminosities and star formation rates (SFRs), or upper limits, for all 82 SHIELD galaxies. We also present, for the first time, deep broadband and continuum-subtracted H-alpha images plus a summary of the properties for the entire sample. Our analysis of the H-alpha data re-affirms previous results which show that at low levels of star formation (log(SFR_{H-alpha}) < -2.5), H-alpha becomes an increasingly poor tracer of the recent average SFR as measured by far-UV (FUV) luminosities. However, we show that this effect is not strictly correlated with the mass of the galaxy. Some very low-mass SHIELD galaxies with higher H-alpha-based SFRs show good agreement with SFR_{FUV}. The SHIELD galaxies show no correlation between H-alpha SFR and gas mass fraction, but reveal a modest correlation between H-alpha specific SFR and gas mass fraction. Overall, the star formation efficiency exhibited by the SHIELD dwarfs is rather low, despite the gas-rich nature of the sample (68% have M_{gas} > M_{stellar}).

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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

GLOW II: A Census of Oxygen in Low-Mass Galaxies

Oxygen is forged by stars and redistributed through galaxies by feedback-driven outflows, leaving a record of star formation and the baryon cycle imprinted on its present-day abundance and distribution. The Galaxies Losing Oxygen via Winds (GLOW) project quantifies the production, distribution, and retention of oxygen in 37 low-mass, low-metallicity, gas-rich galaxies in the nearby universe (D<6 Mpc) spanning a critical stellar mass range (10^6.5 0.5) and within 1 Mpc of a massive galaxy (Mstar>10^9 Msun), indicating environment likely affects the amount of oxygen retained, recycled, or accreted to galaxies. Contrary to expectations, oxygen retention does not correlate with position on the mass-metallicity relation. Although ionized oxygen is detected in the CGM, it remains unclear whether most missing oxygen resides there or has been expelled entirely. Hydrodynamical simulations, despite successfully reproducing the mass-metallicity relation, predict much higher retention fractions than measured in low-mass galaxies. Simple modeling indicates that wind mass-loading and outflow metallicity govern oxygen retention, and that low-mass galaxies accrete less baryonic material relative to the cosmic baryon fraction.

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arXiv2026

GLOW I: Comprehensive Measurements of Gas-Rich, Star-Forming, Low-Mass Galaxies in the Nearby Universe

Gas-rich, star-forming, low-mass galaxies in the nearby universe are powerful laboratories for studying baryonic physics in detail including: stellar mass assembly, stellar feedback, chemical enrichment, and the interplay of the interstellar medium with star formation. Investigating these disparate yet interconnected processes requires data obtained by myriad observatories. Here, we present a comprehensive atlas of uniformly processed data on 37 low-mass galaxies within 6 Mpc. The atlas includes archival data on (i) the HI from the Very Large Array observatory; (ii) resolved stars from Hubble Space Telescope optical imaging; (iii) Spitzer Space Telescope 3.6 micron imaging; and (iv) optical imaging from ground-based telescopes. We also compile measurements of (i) tip-of-the-red-giant-branch (TRGB) distances to the galaxies; (ii) direct method gas-phase oxygen abundances and nitrogen to oxygen abundance ratios; (iii) constraints on the local environment around each galaxy; and (iv) other measurements from the literature. We supplement the data with new observations where needed to complete the measurements for all galaxies in the sample. From these data, we find good agreement between stellar masses measured from color-magnitude diagrams and those estimated from 3.6 micron imaging by assuming a mass-to-light ratio. We also provide the first mapping of the HI profiles as a function of structural parameters. These data sets and measurements are the foundation for the Galaxies Losing Oxygen via Winds (GLOW) project whose main aim is to characterize the star formation - chemical enrichment cycle of low-mass galaxies by measuring the production, distribution, and retention of oxygen on a galaxy-by-galaxy basis.

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arXiv2026

Radial Stellar Age Gradients in 42 Local Volume Dwarf Galaxies

We present radial stellar age gradients measured from star formation histories (SFHs) fit to resolved color-magnitude diagrams (CMDs) of 42 Local Volume dwarfs (6$\lesssim$Log M$_{\star}$/M$_{\odot}$$\lesssim$9), spatially divided into elliptical annuli. Ages in each annulus are quantified using $τ_{90}$ and $τ_{50}$, the lookback times to form 90% and 50% of the cumulative stellar mass. We find that radial age gradients are uncorrelated with environment, but gradients in $τ_{90}$ are significantly correlated ($p$-values$\lesssim$0.001) with lifetime galaxy-wide "global" SFHs, in agreement with two independent cosmological zoom-in simulations. For radial gradients of $τ_{50}$, simulation predictions differ. We demonstrate that given our large (N=42) and diverse observational sample, the strength of an observed correlation with global SFH is an actionable parameter to discriminate between different simulations with differing stellar feedback prescriptions. Overall, our results support predictions that dwarfs form inside-out like their more massive counterparts, with a combination of feedback-driven outward radial stellar migration and increasing birth radii for young stellar populations yielding present-day stellar age gradients ranging from outside-in to flat. In addition, the lack of a correlation between $τ_{50}$ gradients and global SFH argues against recent star formation in radially outflowing gas. We also discuss the impact of differences between our observational sample and samples available in the latest simulations, highlighting areas for future investigation.

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arXiv2026

Scylla: Observational Evidence for an Order of Magnitude in Dust Mass Opacity Evolution with ISM Density in the Large Magellanic Cloud

The emissivity of dust is known to vary greatly with radiative environment, density, grain chemistry, and geometry. Discrepancies between dust mass surface densities derived from far-infrared (FIR) emission and visible extinction persist across and within galaxies in the local Universe. Here, we use new extinction and emission measurements towards the LMC to show that this discrepancy is driven by the dust mass opacity evolving with the intrinsic density of the ISM, and that the ratio between FIR and optical dust mass opacity varies with gas surface density. These new findings imply that the dust mass opacity in the FIR could increase by nearly an order of magnitude (e.g., $κ_{160} = 0.3 - 6\ m^2\ kg^{-2}$) across over an order of magnitude of total hydrogen surface density $(Σ_H = 4 - 100 M_{\odot}\ pc^{-2})$, corroborating previous theoretical models for dust mass opacity evolution in the FIR, and providing new implications for emission-based dust mass estimates.

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arXiv2026

A Unified Framework Connecting Chemical Enrichment to Resolved Star Formation Histories with Applications to Local Group Dwarf Irregulars

We present a new framework for modeling the chemical enrichment histories of galaxies by integrating chemical evolution with resolved star formation histories (SFHs) derived from color-magnitude diagrams. This novel approach links the time evolution of the metallicity of the star-forming ISM to the cumulative stellar mass formed in the galaxy, enabling a self-consistent description of chemical evolution. We apply this methodology to four isolated, gas-rich Local Group dwarf galaxies -- WLM, Aquarius, Leo A, and Leo P -- using deep HST and JWST imaging. For WLM, Aquarius, and Leo A, we independently validate our metallicity evolution results against ages and metallicities of individual red giant stars with spectroscopic measurements. We quantify systematic uncertainties by repeating our analysis with multiple stellar evolution and bolometric correction libraries. We compare the observed chemical enrichment histories to predictions from the TNG50 and FIREbox cosmological hydrodynamic simulations and the Galacticus semi-analytic model. Of our four galaxies, only WLM is sufficiently massive to be reliably represented in these simulations; the remaining three fall below current resolution limits. We find that the enrichment history of WLM is best reproduced by FIREbox, while TNG50 and Galacticus predict higher metallicities at early times, suggesting that differences in stellar feedback and metal recycling prescriptions drive significant variation in predicted enrichment histories. This work demonstrates the power of combining resolved SFHs with physically motivated chemical evolution models to constrain galaxy formation physics and highlights the need for further observational and theoretical studies of metal retention and recycling in low-mass dwarf galaxies.

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arXiv2026

UV Star-Formation Rates of the SHIELD Dwarf Galaxies

The Survey of HI in Extremely Low-mass Dwarfs (SHIELD) is a multi-wavelength observational project targeting gas-rich, star-forming dwarf galaxies at the faint end of the HI mass function. We present near-ultraviolet (NUV) and far-ultraviolet (FUV) flux measurements obtained from GALEX survey images and use these fluxes to derive FUV star-formation rates (SFRs) for all 75 SHIELD galaxies with GALEX data. This paper represents the first published analysis that makes use of the full SHIELD sample. We compare the FUV SFRs to a variety of physical quantities to better understand the nature of SHIELD galaxies. When comparing the H$α$ SFRs to the FUV SFRs for SHIELD and other local galaxy surveys, we confirm and solidify previous results that show that H$α$-based SFRs for dwarf galaxies can grossly underestimate the true rate of star formation, emphasizing the highly stochastic nature of star formation in extremely low-mass galaxies. We further show that FUV SFRs appear to be robust tracers of star formation down to the very lowest galaxy masses included in this study. We show that baryonic mass is the best mass-related tracer for the prediction of the FUV SFR of the galaxies in our sample. Not surprisingly, the SHIELD dwarf galaxies exhibit long gas-depletion timescales and large gas mass fractions: fully 68% of the SHIELD galaxies have gas masses that are larger than their stellar masses.

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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.

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arXiv2026

Other red dots: A possible GLIMPSE of normal AGB stars at Cosmic Noon through extreme lensing

We report the discovery of four extremely faint ($m_{\mathrm{F444W}}\gtrsim29$) red point sources in recent ultra-deep JWST/NIRCam images of the strong lensing galaxy cluster Abell S1063. All four sources sit in lensed arcs, on the symmetry points very close to the critical curves for their host-galaxies' redshifts ($z\sim1-4$). Remarkably, these point sources appear in most arcs that are sufficiently faint close to the critical curve's position ($<21\,\mathrm{nJy}\,\mathrm{arcsec}^{-2}$ in F115W). This suggests that -- unlike previous caustic-crossing events or lensed stars -- thanks to the unprecedented depth of the GLIMPSE observations paired with the extreme lensing magnification (up to $μ\sim10^4$) we might be resolving the lower-mass ($M\sim1-11\,\mathrm{M}_{\odot}$) red stellar population. Concretely, we detect three likely extremely magnified asymptotic giant branch (AGB) stars ($T_{\mathrm{eff}}\sim3200-3750$ K), and one yellow super-giant star ($T_{\mathrm{eff}}\sim6750$ K) -- possibly a yellow hyper-giant or a Cepheid. In addition to offering the first glimpse at low-mass extremely magnified stars, these detections open a possible window into stellar populations, evolution, and chemical enrichment at high redshifts, and could pave the way for using lensed stars such as these as standard candles to populate the distance ladder at cosmological redshifts.

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arXiv2026

Scylla VI: Parsec-Scale Dust Extinction Maps in the SMC and LMC

We present a novel methodology for mapping dust extinction in nearby galaxies at parsec-scale resolution. We apply it to HST 68 fields within the Small and Large Magellanic Clouds (23 fields in the SMC and 45 fields in the LMC) using multi-band HST photometry from the Scylla and METAL surveys. Our technique leverages \textit{kriging}, a geostatistical interpolation method built on the principles of Gaussian Process regression, combined with Gaussian mixture modeling to statistically isolate background stellar sources and account for line-of-sight depth effects. 3D dust simulations demonstrate the method's capability to recover column densities to an accuracy of $A_V \approx 0.1$ mag in fields with at least 1000 sources. The resulting $4^{\prime\prime}$ resolution ($\sim1$-pc) dust maps reveal detailed structure and strong spatial correlation with ancillary ISM tracers, especially in star-forming regions like 30 Doradus. Global extinction of total column densities follows log-normal profiles in both galaxies, with the SMC exhibiting slightly higher mean extinction ($e^μ=0.47$ mag) than the broader LMC ($e^μ=0.43$ mag), likely due to significant line-of-sight depths. We find systematic offsets between dust mass surface densities ($Σ_{D}$) derived from extinction versus FIR emission in both galaxies, with $Σ_{D, FIR}/Σ_{D, A_V}$ ratios ranging from $0.6-1.8$. This work provides the highest-resolution dust extinction maps in SMC and LMC to date, which offer a vital independent benchmark for constraining dust emissivity, $\text{CO}$-dark gas fractions, and the multi-scale structure of the ISM in low-metallicity environments.

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arXiv2026

Scylla at APOGEE: The Impact of Starbursts on the Chemical Evolution of the Magellanic Clouds

Owing to their proximity to the Milky Way, the Large and Small Magellanic Clouds (L/SMC) uniquely probe the evolution of low-mass galaxies undergoing mutual interactions. In this work, we investigate the connection between the star formation histories (SFHs) of the L/SMC measured from HST imaging in the Scylla survey and APOGEE chemical abundances. We model the chemical evolution of the L/SMC in the [Mg/Fe]-[Fe/H] plane within a robust statistical framework to predict chemical abundance signatures resulting directly from starbursts in Scylla SFHs. Both the L/SMC rapidly enrich to high metallicity ([Fe/H] $\gtrsim$ $-1$) within 3 Gyr, followed by slower chemical evolution regulated by sequential starbursts, where the SMC may require higher Fe yields from Type Ia supernovae than the LMC. We also model the [Mg/Fe]-[Fe/H] plane to infer starburst properties across distinct spatial regions in the L/SMC. We identify dominant starbursts in the L/SMC with broadly similar timing, though the SMC may host an earlier burst, and larger burst strength in the LMC. The global starburst properties are nearly uniform across the LMC disk, whereas the dominant SMC population experiences a stronger and later-onset burst in its eastern wing compared to the main body. We also find evidence for a chemically distinct secondary population in the SMC that preferentially traces the foreground and may originate from the LMC. We discuss the implications of these results for the evolutionary history of the L/SMC and for starbursts in interacting low-mass galaxy pairs.

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arXiv2026

The Stellar Initial Mass Function down to 0.16M$_{\odot}$ Towards the Small Magellanic Cloud

The presence (and nature) of variations in the stellar initial mass function (IMF) at substantially sub-solar masses and metallicities ($m$$<$0.5M$_{\odot}$, [M/H]$\lesssim$$-$1) remains poorly constrained. Predictions from simulations vary widely, while observationally, resolved star studies of ultra-faint dwarf galaxies (UFDs) suffer from small sample sizes and background galaxy contamination due to low projected stellar densities. As an alternative metal-poor target, we measure the IMF from resolved stars towards a carefully selected field in the Small Magellanic Cloud (SMC), leveraging a plethora of independent constraints on the target field stellar population including distributions of distance, %extinction, age and metallicity. We resolve $>$15,000 stars down to 0.16M$_{\odot}$ within a single pointing of NIRCam onboard JWST, using an observing strategy that minimizes contamination from point-source-like background galaxies. We explore three different functional forms of the IMF, forward modeling observed color-magnitude diagrams (CMDs) and luminosity functions. We find a best-fit single power law IMF slope of $α$=$-$1.61$^{+0.03}_{-0.03}$, consistent with UFDs probed down to similar limiting masses. Fitting a broken power law IMF, we find low- and high-mass slopes of $α_{1}$=$-$1.44$^{+0.04}_{-0.04}$, $α_{2}$=$-$2.17$^{+0.11}_{-0.11}$ respectively, consistent with solar neighborhood values. Assuming a lognormal IMF, we find a characteristic mass and lognormal width of $m_{c}$=0.12$^{+0.03}_{-0.03}$M$_{\odot}$, $σ$=0.61$^{+0.07}_{-0.06}$M$_{\odot}$, allowing for characteristic masses lower than local values as seen in some simulations as well as low-metallicity Galactic clusters. Lastly, we quantify the impact of assumptions required in our analysis and discuss potential future improvements.

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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.

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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

GLIMPSE-DDT spectroscopic properties of faint-end galaxies at $z\sim6$: Towards first metal enrichment, dust production, and ionizing photon production

Ultra-faint galaxies at high-$z$ are fundamental elements of the early galaxy assembly, and spectroscopic characterization of this population is essential to understand the earliest galaxy evolution. Leveraging the ultra-deep JWST/NIRCam and NIRSpec observations of a gravitational lensing field of Abell S1063, taken as part of the GLIMPSE survey, we present spectroscopic properties of 16 galaxies fainter than $M_{\rm UV}=-17$ mag, including the metallicity, dust attenuation, and the ionizing photon production efficiency. The emission lines are generally quite strong, roughly half of which cannot be replicated with standard stellar populations and require an extreme ionizing source. We also identify relatively strong [OIII] emission lines from all sample galaxies, which indicates that the low-mass end of the mass-metallicity relation is extended down to $M_\star\sim10^6\ M_\odot$ at $z\sim6$. The strong [OIII] line detection from the lowest-mass galaxy among the sample ($M_\star\sim10^{5.6}\ M_\odot$) stands in contrast to recent reports of extremely metal-poor galaxy candidates at similar mass and redshift, suggesting that there could be two distinct pathways of the earliest metal enrichment as simulations have predicted. Interestingly, we detect both dust attenuation and galactic outflow in one of the sample galaxies with $M_\star=10^{6.6}\ M_\odot$ at $z=5.5$. All the dust, metal, and outflow contents in this galaxy can be consistently explained by supernovae (SNe), indicative of the key roles of SNe in the earliest galaxy assembly such as dust production, metal enrichment, stellar feedback, and baryon cycle.

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