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We present a detailed stellar population analysis of 11 bright (H < 26.6) galaxies at z = 9–11 (three spectroscopically confirmed) to constrain the chemical enrichment and growth of stellar mass of early galaxies. We use the flexible Bayesian spectral energy distribution (SED) fitting code Prospector with a range of star formation histories (SFHs), a flexible dust attenuation law, and a self-consistent model of emission lines. This approach allows us to assess how different priors affect our results and how well we can break degeneracies between dust attenuation, stellar ages, metallicity, and emission lines using data that probe only the rest-frame ultraviolet (UV) to optical wavelengths. We measure a median observed UV spectral slope β=−1.87−0.43+0.35 for relatively massive star-forming galaxies ( 9 10.

The long-duration Galactic-bulge microlensing event OGLE-2011-BLG-0462 produced relativistic astrometric deflections of the source star, which we measured using Hubble Space Telescope (HST) observations taken at eight epochs over ∼6 yr. Analysis of the microlensing light curve and astrometry led our group (followed by other independent groups) to conclude that the lens is an isolated stellar-mass black hole (BH)—the first and only one unambiguously discovered to date. There have now been three additional epochs of HST observations, increasing the astrometric time baseline to 11 yr. Additionally, the ground-based OGLE data have been updated. We have reanalyzed the data, including the new HST astrometry, and photometry obtained with 16 different telescopes. The source lies only 0.″4 from a bright neighbor, making it crucial to perform precise subtraction of its point-spread function (PSF) in the astrometric measurements of the source. Moreover, we show that it is essential to perform a separate PSF subtraction for each individual HST frame as part of the reductions. Our final solution yields a lens mass of 7.15 ± 0.83 M⊙. Combined with the lack of detected light from the lens at late HST epochs, the BH nature of the lens is conclusively verified. The BH lies at a distance of 1.52 ± 0.15 kpc, and it is moving with a space velocity of 51.1 ± 7.5 km s−1 relative to the stars in the neighborhood. We compare our results with those of other studies and discuss reasons for the differences. We also searched for binary companions of the BH at a range of separations, but found no evidence for any.

We present the first comprehensive release of photometric redshifts (photo- z's) from the Cosmic Assembly Near-Infrared Deep Extragalactic Legacy Survey (CANDELS) team. We use statistics based upon the Quantile–Quantile (Q–Q) plot to identify biases and signatures of underestimated or overestimated errors in photo- z probability density functions (PDFs) produced by six groups in the collaboration; correcting for these effects makes the resulting PDFs better match the statistical definition of a PDF. After correcting each group’s PDF, we explore three methods of combining the different groups’ PDFs for a given object into a consensus curve. Two of these methods are based on identifying the minimum f-divergence curve, i.e., the PDF that is closest in aggregate to the other PDFs in a set (analogous to the median of an array of numbers). We demonstrate that these techniques yield improved results using sets of spectroscopic redshifts independent of those used to optimize PDF modifications. The best photo- z PDFs and point estimates are achieved with the minimum f-divergence using the best four PDFs for each object (mFDa4) and the hierarchical Bayesian (HB4) methods, respectively. The HB4 photo- z point estimates produced σ NMAD = 0.0227/0.0189 and ∣Δz/(1 + z)∣ > 0.15 outlier fraction = 0.067/0.019 for spectroscopic and 3D Hubble Space Telescope redshifts, respectively. Finally, we describe the structure and provide guidance for the use of the CANDELS photo- z catalogs, which are available at https://archive.stsci.edu/prepds/candels/.

We present measurements of the rest-frame UV spectral slope, β, for a sample of 36 faint star-forming galaxies at z ∼ 9–16 discovered in one of the deepest JWST NIRCam surveys to date, the Next Generation Deep Extragalactic Exploratory Public Survey. We use robust photometric measurements for UV-faint galaxies (down to M UV ∼ −16), originally published in Leung et al., and measure values of the UV spectral slope via photometric power-law fitting to both the observed photometry and stellar population models obtained through spectral energy distribution (SED) fitting with Bagpipes. We obtain a median and 68% confidence interval for β from photometric power-law fitting of βPL=−2.7−0.5+0.5 and from SED fitting, βSED=−2.3−0.1+0.2 for the full sample. We show that when only two to three photometric detections are available, SED fitting has a lower scatter and reduced biases than photometric power-law fitting. We quantify this bias and find that after correction the median βSED,corr=−2.5−0.2+0.2 . We measure physical properties for our galaxies with Bagpipes and find that our faint ( MUV=−18.1−0.9+0.7 ) sample is low in mass ( log[M*/M⊙]=7.7−0.5+0.5 ), fairly dust-poor ( Av=0.1−0.1+0.2 mag), and modestly young ( log[age]=7.8−0.8+0.2 yr) with a median star formation rate of log(SFR)=−0.3−0.4+0.4M⊙yr−1 . We find no strong evidence for ultrablue UV spectral slopes (β ∼ −3) within our sample, as would be expected for exotically metal-poor (Z/Z ⊙ < 10−3) stellar populations with very high Lyman continuum escape fractions. Our observations are consistent with model predictions that galaxies of these stellar masses at z ∼ 9–16 should have only modestly low metallicities (Z/Z ⊙ ∼ 0.1–0.2).

One of the fundamental questions of cosmology is the origin and mechanism(s) responsible for the reionization of the Universe beyond z ∼ 6. Many studies have focused on Hubble Space Telescope (HST) Cosmic Origins Spectrograph (COS) observations of local (z ∼ 0.3) galaxies emitting ionizing radiation (Lyman continuum, or LyC) for insight. However, LyC measurements can depend on chance alignment of optically thin channels with the observer. In addition, low signal in the spectra of these faint LyC emitters inhibits constraints on gas geometry and stellar populations. To circumvent these limitations, we analyze stacks of a consolidated sample of HST/COS observations of the LyC in 89 galaxies at z ∼ 0.3. From fitting of the continuum, we obtain information about the underlying stellar populations, emergent LyC, and neutral interstellar medium geometry. We find that most LyC nondetections are not leaking appreciable LyC ( fescLyC < 1%), but also that exceptional cases point to spatial variations in the LyC escape fraction fescLyC . Stellar populations younger than 3 Myr lead to an increase in ionizing feedback, which in turn increases the isotropy of LyC escape. Wolf–Rayet stars and 3–6 Myr populations appear to play little role in LyC escape. Mechanical feedback from supernovae in 8–10 Myr stellar populations is important for anisotropic gas distributions needed for LyC escape. While mechanical feedback is necessary for any LyC escape, high fescLyC (>5%) also requires a confluence of young stars and ionizing feedback. A two-stage burst of star formation is critical to producing this optimal LyC escape scenario, and should be considered fundamental to identifying LyC emitters at the Epoch of Reionization.

We performed spectroscopic analyses of five local compact star-forming galaxies (CSFGs) with extremely high [O iii]/[O ii] (O32) ratios (>20). These targets remarkably share similar properties with high-redshift C iv emitters at z > 6: high Hβ equivalent widths (EWs > 200Å), extreme O32 ratios, low metallicities (12+log(O/H) ≲ 7.8), low C/O abundances (log(C/O) < −0.7), and high ionization conditions (logU > −2). The ultraviolet (UV) spectra were acquired using the Hubble Space Telescope’s (HST) Cosmic Origins Spectrograph and Space Telescope Imaging Spectrograph. We have identified a wealth of rest-frame UV emission lines (C iv, He ii, O iii], C iii]) in the HST spectra. Notably, all our targets show intense C iv emission lines with rest-frame EWs > 10 Å, indicative of hard ionizing radiation. The rest-frame UV emission line diagnostics disfavor an active galactic nucelus and could be consistent with significant shock contributions to the source of ionizing radiation. Four of our targets show high C iv/C iii] ratios (≥1.4), suggestive of strong Lyman-continuum leakage (LyC escape fraction, fesc,LyC > 10%) from these sources. This is consistent with their Lyα-inferred LyC escape fractions (fesc,LyC = 9%–31%). We derive relative C/O abundances from our sources, showing log(C/O) values from −1.28 to −0.77, comparable to those of reionization-era galaxies at z ≳ 6. The properties of the CSFGs, particularly their intense C iv emission and high O32 ratios, which suggest significant LyC escape fractions, are similar to those of the reionization-era C iv emitters. These similarities reinforce the hypothesis that these CSFGs are the closest analogs of significant contributors to the reionization of the intergalactic medium.

In the next decade, deep galaxy surveys from telescopes such as the James Webb Space Telescope and Roman Space Telescope will provide transformational data sets that will greatly enhance the understanding of galaxy formation during the epoch of reionization (EoR). In this work, we present the Deep Realistic Extragalactic Model (DREaM) for creating synthetic galaxy catalogs. Our model combines dark matter simulations, subhalo abundance matching and empirical models, and includes galaxy positions, morphologies, and spectral energy distributions. The resulting synthetic catalog extends to redshifts z ∼ 12, and galaxy masses log10(M/M⊙)=5 covering an area of 1 deg2 on the sky. We use DREaM to explore the science returns of a 1 deg2 Roman ultra-deep field (UDF), and to provide a resource for optimizing ultra-deep survey designs. We find that a Roman UDF to ∼30 m AB will potentially detect more than 106 M UV < − 17 galaxies, with more than 104 at redshifts z > 7, offering an unparalleled data set for constraining galaxy properties during the EoR. Our synthetic catalogs and simulated images are made publicly available to provide the community with a tool to prepare for upcoming data.

We study the spatially resolved stellar populations of 444 galaxies at 0.3 < z < 6.0 in two clusters (WHL 0137–08 and MACS 0647+70) and a blank field, combining imaging data from the Hubble Space Telescope and JWST to perform spatially resolved spectral energy distribution (SED) modeling using piXedfit. The high spatial resolution of the imaging data combined with magnification from gravitational lensing in the cluster fields allows us to resolve a large fraction of our galaxies (109) to subkiloparsec scales. At redshifts around cosmic noon and higher (2.5 ≲ z ≲ 6.0), we find mass-doubling times to be independent of radius, inferred from flat specific star formation rate (sSFR) radial profiles and similarities between the half-mass and half-SFR radii. At lower redshifts (1.5 ≲ z ≲ 2.5), a significant fraction of our star-forming galaxies shows evidence for nuclear starbursts, inferred from a centrally elevated sSFR and a much smaller half-SFR radius compared to the half-mass radius. At later epochs, we find more galaxies suppress star formation in their centers but are still actively forming stars in the disk. Overall, these trends point toward a picture of inside-out galaxy growth consistent with theoretical models and simulations. We also observe a tight relationship between the central mass surface density and global stellar mass with ∼0.38 dex scatter. Our analysis demonstrates the potential of spatially resolved SED analysis with JWST data. Future analysis with larger samples will be able to further explore the assembly of galaxy mass and the growth of their structures.

We present an overview of the CANDELS Lyα Emission At Reionization (CLEAR) survey. CLEAR is a 130 orbit program of the Hubble Space Telescope using the Wide Field Camera 3 (WFC3) IR G102 grism. CLEAR targets 12 pointings divided between the GOODS-N and GOODS-S fields of the Cosmic Assembly Near-IR Deep Extragalactic Legacy Survey (CANDELS). Combined with existing spectroscopic data from other programs, the full CLEAR data set includes spectroscopic imaging of these fields over 0.8–1.7 μm. In this paper, we describe the CLEAR survey, the survey strategy, the data acquisition, reduction, processing, and science products and catalogs released alongside this paper. The catalogs include emission line fluxes and redshifts derived from the combination of the photometry and grism spectroscopy for 6048 galaxies, primarily ranging from 0.2 ≲ z ≲ 3. We also provide an overview of CLEAR’s science goals and results. In conjunction with this paper we provide links to electronic versions of the data products, including 1D+2D extracted spectra and emission line maps.

Low-mass galaxies can significantly contribute to reionization due to their potentially high Lyman continuum (LyC) escape fraction and relatively high space density. We present a constraint on the LyC escape fraction from low-mass galaxies at z = 1.3–3.0. We obtained rest-frame UV continuum imaging with the ACS/SBC and the WFC3/UVIS from the Hubble Space Telescope for eight strongly lensed galaxies that were identified in the Sloan Giant Arc Survey and the Cluster Lensing and Supernova survey with Hubble. The targeted galaxies were selected to be spectroscopically confirmed, highly magnified, and blue in their UV spectral shapes (β < −1.7). Our targets include intrinsically low-luminosity galaxies down to a magnification-corrected absolute UV magnitude M UV ∼ −14. We perform custom-defined aperture photometry to place the most reliable upper limits of LyC escape from our sample. From our observations, we report no significant (>2σ) detections of LyC fluxes, placing 1σ upper limits on the absolute LyC escape fractions of 3%–15%. Our observations do not support the expected increased escape fractions of LyC photons from intrinsically UV faint sources. Considering the highly anisotropic geometry of LyC escape, increasing the sample size of faint galaxies in future LyC observations is crucial.