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ABSTRACT We present novel constraints on the underlying galaxy formation physics (e.g. mass-loading factor, star formation history, and metal retention) at z ≳ 7 for the low-mass (M* ∼ 105 M⊙) Local Group ultrafaint dwarf galaxy (UFD) Eridanus ii (Eri ii). Using a hierarchical Bayesian framework, we apply a one-zone chemical evolution model to Eri ii’s CaHK-based photometric metallicity distribution function (MDF; [Fe/H]) and find that the evolution of Eri ii is well characterized by a short, exponentially declining star formation history ($$\tau _\text{SFH}=0.39\pm _{0.13}^{0.18}$$ Gyr), a low star formation efficiency ($$\tau _\text{SFE}=27.56\pm _{12.92}^{25.14}$$ Gyr), and a large mass-loading factor ($$\eta =194.53\pm _{42.67}^{33.37}$$). Our results are consistent with Eri ii forming the majority of its stars before the end of reionization. The large mass-loading factor implies strong outflows in the early history of Eri ii and is in good agreement with theoretical predictions for the mass scaling of galactic winds. It also results in the ejection of >90 per cent of the metals produced in Eri ii. We make predictions for the distribution of [Mg/Fe]–[Fe/H] in Eri ii as well as the prevalence of ultra metal-poor stars, both of which can be tested by future chemical abundance measurements. Spectroscopic follow-up of the highest metallicity stars in Eri ii ([Fe/H] > −2) will greatly improve model constraints. Our new framework can readily be applied to all UFDs throughout the Local Group, providing new insights into the underlying physics governing the evolution of the faintest galaxies in the reionization era. 

Abstract We present uniformly measured stellar metallicities of 463 stars in 13 Milky Way (MW) ultra-faint dwarf galaxies (UFDs;M_V= −7.1 to −0.8) using narrowband CaHK (F395N) imaging taken with the Hubble Space Telescope. This represents the largest homogeneous set of stellar metallicities in UFDs, increasing the number of metallicities in these 13 galaxies by a factor of 5 and doubling the number of metallicities in all known MW UFDs. We provide the first well-populated MDFs for all galaxies in this sample, with 〈[Fe/H]〉 ranging from −3.0 to −2.0 dex, andσ_[Fe/H]ranging from 0.3–0.7 dex. We find a nearly constant [Fe/H]∼ −2.6 over 3 decades in luminosity (∼10²–10⁵L_⊙), suggesting that the mass–metallicity relationship does not hold for such faint systems. We find a larger fraction (24%) of extremely metal-poor ([Fe/H]< −3) stars across our sample compared to the literature (14%), but note that uncertainties in our most metal-poor measurements make this an upper limit. We find 19% of stars in our UFD sample to be metal-rich ([Fe/H] > −2), consistent with the sum of literature spectroscopic studies. MW UFDs are known to be predominantly >13 Gyr old, meaning that all stars in our sample are truly ancient, unlike metal-poor stars in the MW, which have a range of possible ages. Our UFD metallicities are not well matched to known streams in the MW, providing further evidence that known MW substructures are not related to UFDs. We include a catalog of our stars to encourage community follow-up studies, including priority targets for ELT-era observations. 

Abstract We present the elemental abundances and ages of 19 massive quiescent galaxies atz∼ 1.4 andz∼ 2.1 from the Keck Heavy Metal Survey. The ultradeep LRIS and MOSFIRE spectra were modeled using a full-spectrum stellar population fitting code with variable abundance patterns. The galaxies have iron abundances between [Fe/H] = −0.5 and −0.1 dex, with typical values of −0.2 [−0.3] atz∼ 1.4 [z∼ 2.1]. We also find a tentative $\log {\sigma }_v$–[Fe/H] relation atz∼ 1.4. The magnesium-to-iron ratios span [Mg/Fe] = 0.1–0.6 dex, with typical values of 0.3 [0.5] dex atz∼ 1.4 [z∼ 2.1]. The ages imply formation redshifts ofz_form= 2–8. Compared to quiescent galaxies at lower redshifts, we find that [Fe/H] was ∼0.2 dex lower atz= 1.4–2.1. We find no evolution in [Mg/Fe] out toz∼ 1.4, though thez∼ 2.1 galaxies are 0.2 dex enhanced compared toz= 0–0.7. A comparison of these results to a chemical evolution model indicates that galaxies at higher redshift form at progressively earlier epochs and over shorter star formation timescales, with thez∼ 2.1 galaxies forming the bulk of their stars over 150 Myr atz_form∼ 4. This evolution cannot be solely attributed to an increased number of quiescent galaxies at later times; several Heavy Metal galaxies have extreme chemical properties not found in massive galaxies atz∼ 0.0–0.7. Thus, the chemical properties of individual galaxies must evolve over time. Minor mergers also cannot fully account for this evolution as they cannot increase [Fe/H], particularly in galaxy centers. Consequently, the buildup of massive quiescent galaxies sincez∼ 2.1 may require further mechanisms, such as major mergers and/or central star formation. 

We present elemental abundance patterns (C, N, Mg, Si, Ca, Ti, V, Cr, Fe, Co, and Ni) for a population of 135 massive quiescent galaxies at z ∼ 0.7 with ultra-deep rest-frame optical spectroscopy drawn from the LEGA-C survey. We derive average ages and elemental abundances in four bins of stellar velocity dispersion (σv) ranging from 150–250 km s−1 using a full-spectrum hierarchical Bayesian model. The resulting elemental abundance measurements are precise to 0.05 dex. The majority of elements, as well as the total metallicity and stellar age, show a positive correlation with σv. Thus, the highest dispersion galaxies formed the earliest and are the most metal-rich. We find only mild or nonsignificant trends between [X/Fe] and σv, suggesting that the average star formation timescale does not strongly depend on velocity dispersion. To first order, the abundance patterns of the z ∼ 0.7 quiescent galaxies are strikingly similar to those at z ∼ 0. However, at the lowest-velocity dispersions, the z ∼ 0.7 galaxies have slightly enhanced N, Mg, Ti, and Ni abundance ratios and earlier formation redshifts than their z ∼ 0 counterparts. Thus, while the higher-mass quiescent galaxy population shows little evolution, the low-mass quiescent galaxies population has grown significantly over the past 6 Gyr. Finally, the abundance patterns of both z ∼ 0 and z ∼ 0.7 quiescent galaxies differ considerably from theoretical prediction based on a chemical evolution model, indicating that our understanding of the enrichment histories of these galaxies is still very limited. 

Abstract We present elemental abundance patterns (C, N, Mg, Si, Ca, Ti, V, Cr, Fe, Co, and Ni) for a population of 135 massive quiescent galaxies atz∼ 0.7 with ultra-deep rest-frame optical spectroscopy drawn from the LEGA-C survey. We derive average ages and elemental abundances in four bins of stellar velocity dispersion (σ_v) ranging from 150–250 km s⁻¹using a full-spectrum hierarchical Bayesian model. The resulting elemental abundance measurements are precise to 0.05 dex. The majority of elements, as well as the total metallicity and stellar age, show a positive correlation withσ_v. Thus, the highest dispersion galaxies formed the earliest and are the most metal-rich. We find only mild or nonsignificant trends between [X/Fe] andσ_v, suggesting that the average star formation timescale does not strongly depend on velocity dispersion. To first order, the abundance patterns of thez∼ 0.7 quiescent galaxies are strikingly similar to those atz∼ 0. However, at the lowest-velocity dispersions, thez∼ 0.7 galaxies have slightly enhanced N, Mg, Ti, and Ni abundance ratios and earlier formation redshifts than theirz∼ 0 counterparts. Thus, while the higher-mass quiescent galaxy population shows little evolution, the low-mass quiescent galaxies population has grown significantly over the past 6 Gyr. Finally, the abundance patterns of bothz∼ 0 andz∼ 0.7 quiescent galaxies differ considerably from theoretical prediction based on a chemical evolution model, indicating that our understanding of the enrichment histories of these galaxies is still very limited. 

ABSTRACT Planck data provide precise constraints on cosmological parameters when assuming the base ΛCDM model, including a 0.17 per cent measurement of the age of the Universe, $$t_0=13.797 \pm 0.023\, {\rm Gyr}$$. However, the persistence of the ‘Hubble tension’ calls the base ΛCDM model’s completeness into question and has spurred interest in models such as early dark energy (EDE) that modify the assumed expansion history of the Universe. We investigate the effect of EDE on the redshift–time relation z↔t and find that it differs from the base ΛCDM model by at least $${\approx } 4{{\ \rm per\ cent}}$$ at all t and z. As long as EDE remains observationally viable, any inferred t ← z or z ← t quoted to a higher level of precision do not reflect the current status of our understanding of cosmology. This uncertainty has important astrophysical implications: the reionization epoch – 10 > z > 6 – corresponds to disjoint lookback time periods in the base ΛCDM and EDE models, and the EDE value of t0 = 13.25 ± 0.17 Gyr is in tension with published ages of some stars, star clusters, and ultrafaint dwarf galaxies. However, most published stellar ages do not include an uncertainty in accuracy (due to, e.g. uncertain distances and stellar physics) that is estimated to be $$\sim 7\!-\!10{{\ \rm per\ cent}}$$, potentially reconciling stellar ages with $$t_{0,\rm EDE}$$. We discuss how the big data era for stars is providing extremely precise ages ($$\lt 1{{\ \rm per\ cent}}$$) and how improved distances and treatment of stellar physics such as convection could result in ages accurate to $$4\!-\!5{{\ \rm per\ cent}}$$, comparable to the current accuracy of t↔z. Such precise and accurate stellar ages can provide detailed insight into the high-redshift Universe independent of a cosmological model. 

Abstract We present NIRCam and NIRISS modules for DOLPHOT, a widely used crowded-field stellar photometry package. We describe details of the modules including pixel masking, astrometric alignment, star finding, photometry, catalog creation, and artificial star tests. We tested these modules using NIRCam and NIRISS images of M92 (a Milky Way globular cluster), Draco II (an ultrafaint dwarf galaxy), and Wolf–Lundmark–Mellote (a star-forming dwarf galaxy). DOLPHOT’s photometry is highly precise, and the color–magnitude diagrams are deeper and have better definition than anticipated during original program design in 2017. The primary systematic uncertainties in DOLPHOT’s photometry arise from mismatches in the model and observed point-spread functions (PSFs) and aperture corrections, each contributing ≲0.01 mag to the photometric error budget. Version 1.2 of WebbPSF models, which include charge diffusion and interpixel capacitance effects, significantly reduced PSF-related uncertainties. We also observed minor (≲0.05 mag) chip-to-chip variations in NIRCam’s zero-points, which will be addressed by the JWST flux calibration program. Globular cluster observations are crucial for photometric calibration. Temporal variations in the photometry are generally ≲0.01 mag, although rare large misalignment events can introduce errors up to 0.08 mag. We provide recommended DOLPHOT parameters, guidelines for photometric reduction, and advice for improved observing strategies. Our Early Release Science DOLPHOT data products are available on MAST, complemented by comprehensive online documentation and tutorials for using DOLPHOT with JWST imaging data. 

Abstract We investigate dust attenuation and its dependence on viewing angle for 308 star-forming galaxies at 1.3 ≤z≤ 2.6 from the MOSFIRE Deep Evolution Field survey. We divide galaxies with a detected Hαemission line and coverage of Hβinto eight groups by stellar mass, star formation rate (SFR), and inclination (i.e., axis ratio), and we then stack their spectra. From each stack, we measure the Balmer decrement and gas-phase metallicity, and then we compute the medianA_Vand UV continuum spectral slope (β). First, we find that none of the dust properties (Balmer decrement,A_V, orβ) varies with the axis ratio. Second, both stellar and nebular attenuation increase with increasing galaxy mass, showing little residual dependence on SFR or metallicity. Third, nebular emission is more attenuated than stellar emission, and this difference grows even larger at higher galaxy masses and SFRs. Based on these results, we propose a three-component dust model in which attenuation predominantly occurs in star-forming regions and large, dusty star-forming clumps, with minimal attenuation in the diffuse ISM. In this model, nebular attenuation primarily originates in clumps, while stellar attenuation is dominated by star-forming regions. Clumps become larger and more common with increasing galaxy mass, creating the above mass trends. Finally, we argue that a fixed metal yield naturally leads to mass regulating dust attenuation. Infall of low-metallicity gas increases the SFR and lowers the metallicity, but leaves the dust column density mostly unchanged. We quantify this idea using the Kennicutt–Schmidt and fundamental metallicity relations, showing that galaxy mass is indeed the primary driver of dust attenuation. 

ABSTRACT We perform cosmological hydrodynamical simulations to study the formation of proto-globular cluster candidates in progenitors of present-day dwarf galaxies $$(M_{\rm vir} \approx 10^{10}\, {\rm M}_\odot$$ at z = 0) as part of the ‘Feedback in Realistic Environment’ (FIRE) project. Compact (r1/2 < 30 pc), relatively massive (0.5 × 105 ≲ M⋆/M⊙ ≲ 5 × 105), self-bound stellar clusters form at 11 ≳ z ≳ 5 in progenitors with $$M_{\rm vir} \approx 10^9\, \mathrm{M}_{\odot }$$. Cluster formation is triggered when at least $$10^7\, \mathrm{M}_{\odot }$$ of dense, turbulent gas reaches $$\Sigma _{\rm gas} \approx 10^4\, {\rm M}_\odot \, {\rm pc}^{-2}$$ as a result of the compressive effects of supernova feedback or from cloud–cloud collisions. The clusters can survive for $$2-3\, {\rm Gyr}$$; absent numerical effects, they could possibly survive substantially longer, perhaps to z = 0. The longest lived clusters are those that form at significant distance – several hundreds of pc – from their host galaxy. We therefore predict that globular clusters forming in progenitors of present-day dwarf galaxies will be offset from any pre-existing stars within their host dark matter haloes as opposed to deeply embedded within a well-defined galaxy. Properties of the nascent clusters are consistent with observations of some of the faintest and most compact high-redshift sources in Hubble Space Telescope lensing fields and are at the edge of what will be detectable as point sources in deep imaging of non-lensed fields with JWST. By contrast, the star clusters’ host galaxies will remain undetectable. 

Abstract We construct a catalog of star clusters from Hubble Space Telescope images of the inner disk of the Triangulum Galaxy (M33) using image classifications collected by the Local Group Cluster Search, a citizen science project hosted on the Zooniverse platform. We identify 1214 star clusters within the Hubble Space Telescope imaging footprint of the Panchromatic Hubble Andromeda Treasury: Triangulum Extended Region (PHATTER) survey. Comparing this catalog to existing compilations in the literature, 68% of the clusters are newly identified. The final catalog includes multiband aperture photometry and fits for cluster properties via integrated light spectral energy distribution fitting. The cluster catalog’s 50% completeness limit is ∼1500 M ☉ at an age of 100 Myr, as derived from comprehensive synthetic cluster tests.