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We present spectroscopic confirmation of an ultra-massive galaxy (UMG) with $\log(M_\star/M_\odot) = 10.98 \pm 0.07$ at $z_\mathrm{spec} = 4.8947$ in the Extended Groth Strip (EGS), based on deep observations of Ly$\alpha$ emission with Keck/DEIMOS. The ultra-massive galaxy (UMG-28740) is the most massive member in one of the most significant overdensities in the EGS, with four additional photometric members with $\log(M_\star/M_\odot) > 10.5$ within $R_\mathrm{proj} \sim 1$ cMpc. Spectral energy distribution (SED) fitting using a large suite of star formation histories and two sets of high-quality photometry from ground- and space-based facilities consistently estimates the mass of this object to be $\log(M_\star/M_\odot) \sim 11$ with a small standard deviation between measurements ($\sigma = 0.07$). While the best-fit SED models agree on stellar mass, we find discrepancies in the estimated star formation rate for UMG-28740, resulting in either a star-forming or quiescent system. $\mathit{JWST}$/NIRCam photometry of UMG-28740 strongly favors a quiescent scenario, demonstrating the need for high-quality mid-IR observations. Assuming the galaxy to be quiescent, UMG-28740 formed the bulk of its stars at $z > 10$ and is quenching at $z \sim 8$, resulting in a high star formation efficiency at high redshift ($\epsilon \sim 0.2$ at $z \sim 5$ and $\epsilon \gtrsim 1$ at $z \gtrsim 8$). As the most massive galaxy in its protocluster environment, UMG-28740 is a unique example of the impossibly early galaxy problem.

Abstract Here we present a sample of 12 massive quiescent galaxy candidates at $$z\sim 3-4$$ z ∼ 3 - 4 observed with the James Webb Space Telescope (JWST) Near Infrared Spectrograph (NIRSpec). These galaxies were pre-selected from the Hubble Space Telescope imaging and 10 of our sources were unable to be spectroscopically confirmed by ground based spectroscopy. By combining spectroscopic data from NIRSpec with multi-wavelength imaging data from the JWST Near Infrared Camera (NIRCam), we analyse their stellar populations and their formation histories. We find that all of our galaxies classify as quiescent based on the reconstruction of their star formation histories but show a variety of quenching timescales and ages. All our galaxies are massive ( $$\sim 0.1-1.2\times 10^{11}$$ ∼ 0.1 - 1.2 × 10 11 M $$_\odot$$ ⊙ ), with masses comparable to massive galaxies in the local Universe. We find that the oldest galaxy in our sample formed $$\sim 1.0\times 10^{11}$$ ∼ 1.0 × 10 11 M $$_\odot$$ ⊙ of mass within the first few hundred million years of the Universe and has been quenched for more than a billion years by the time of observation at $$z\sim 3.2$$ z ∼ 3.2 ( $$\sim 2$$ ∼ 2 billion years after the Big Bang). Our results point to very early formation of massive galaxies requiring a high conversion rate of baryons to stars in the early Universe.

We present a measurement of the low-mass quiescent size–mass relation at cosmic noon (1 < z < 3) from the JWST PRIMER and UNCOVER treasury surveys, which highlights two distinct classes of quiescent galaxies. While the massive population is well studied at these redshifts, the low-mass end has been previously underexplored due to a lack of observing facilities with sufficient sensitivity and spatial resolution. We select a conservative sample of low-mass quiescent galaxy candidates using rest-frame UVJ colors and specific star formation rate criteria and measure galaxy morphology in both rest-frame UV/optical wavelengths (F150W) and rest-frame near-infrared (F444W). We confirm an unambiguous flattening of the low-mass quiescent size–mass relation, which results from the separation of the quiescent galaxy sample into two distinct populations at $\mathrm{log}({M}_{\star }/{M}_{\odot })\sim 10.3$ : low-mass quiescent galaxies that are notably younger and have disky structures, and massive galaxies consistent with spheroidal morphologies and older median stellar ages. These separate populations imply mass quenching dominates at the massive end while other mechanisms, such as environmental or feedback-driven quenching, form the low-mass end. This stellar mass-dependent slope of the quiescent size–mass relation could also indicate a shift from size growth due to star formation (low masses) to growth via mergers (massive galaxies). The transition mass between these two populations also corresponds with other dramatic changes and characteristic masses in several galaxy evolution scaling relations (e.g., star formation efficiency, dust obscuration, and stellar-to-halo mass ratios), further highlighting the stark dichotomy between low-mass and massive galaxy formation.

We report the spectroscopic confirmation of a massive ( $\mathrm{log}({M}_{\star }/{M}_{\odot })=10.34{\pm }_{0.07}^{0.06}$ ), Hubble Space Telescope–dark ( m _F150W − m _F444W = 3.6) quiescent galaxy at z _spec = 3.97 in the UNCOVER survey. NIRSpec/PRISM spectroscopy and a nondetection in deep Atacama Large Millimeter/submillimeter Array imaging surprisingly reveals that the galaxy is consistent with a low (

In this paper we describe the survey design for the Ultradeep NIRSpec and NIRCam Observations before the Epoch of Reionization (UNCOVER) Cycle 1 JWST Treasury program, which executed its early imaging component in 2022 November. The UNCOVER survey includes ultradeep (∼29–30AB) imaging of ∼45 arcmin ^2 on and around the well-studied A2744 galaxy cluster at z = 0.308 and will follow up ∼500 galaxies with extremely deep low-resolution spectroscopy with the NIRSpec/PRISM during the summer of 2023, with repeat visits in summer 2024. We describe the science goals, survey design, target selection, and planned data releases. We also present and characterize the depths of the first NIRCam imaging mosaic, highlighting previously unparalleled resolved and ultradeep 2–4 μ m imaging of known objects in the field. The UNCOVER primary NIRCam mosaic spans 28.8 arcmin ^2 in seven filters (F115W, F150W, F200W, F277W, F356W, F410M, and F444W) and 16.8 arcmin ^2 in our NIRISS parallel (F115W, F150W, F200W, F356W, and F444W). To maximize early community use of the Treasury data set, we publicly release the full reduced mosaics of public JWST imaging including 45 arcmin ^2 NIRCam and 17 arcmin ^2 NIRISS mosaics on and around the A2744 cluster, including the Hubble Frontier Field primary and parallel footprints.

We present an overview and first results from the Spectroscopic Ultradeep Survey Probing Extragalactic Near-infrared Stellar Emission (SUSPENSE), executed with NIRSpec on JWST. The primary goal of the SUSPENSE program is to characterize the stellar, chemical, and kinematic properties of massive quiescent galaxies at cosmic noon. In a single deep NIRSpec/MSA configuration, we target 20 distant quiescent galaxy candidates ( z = 1–3, H _AB ≤ 23), as well as 53 star-forming galaxies at z = 1–4. With 16 hr of integration and the G140M-F100LP dispersion-filter combination, we observe numerous Balmer and metal absorption lines for all quiescent candidates. We derive stellar masses (log M _* / M _⊙ ∼ 10.2–11.5) and detailed star formation histories (SFHs) and show that all 20 candidate quiescent galaxies indeed have quenched stellar populations. These galaxies show a variety of mass-weighted ages (0.8–3.3 Gyr) and star formation timescales (∼0.5–4 Gyr), and four out of 20 galaxies were already quiescent by z = 3. On average, the z > 1.75 [ z < 1.75] galaxies formed 50% of their stellar mass before z = 4 [ z = 3]. Furthermore, the typical SFHs of the galaxies in these two redshift bins ( z _mean = 2.2 [1.3]) indicate that galaxies at higher redshift formed earlier and over shorter star formation timescales compared to lower redshifts. Although this evolution is naturally explained by the growth of the quiescent galaxy population over cosmic time, number density calculations imply that mergers and/or late-time star formation also contribute to the evolution. In future work, we will further unravel the early formation, quenching, and late-time evolution of these galaxies by extending this work with studies on their chemical abundances, resolved stellar populations, and kinematics.

We present results from the JWST First Reionization Epoch Spectroscopically Complete Observations survey on the star-forming sequence (SFS) of galaxies at 1.0 < z < 1.7, around the peak of the cosmic star formation history. Star formation rates (SFRs) are measured from the redshifted, relatively dust-insensitive Paschen- α emission line, and stellar mass measurements include the F444W (4.4 μ m; rest-frame H ) band. We find SFRs of galaxies with log( M _* / M _⊙ ) > 9.5 that are lower than found in many earlier studies by up to 0.6 dex, but in good agreement with recent results obtained with the Prospector fitting framework. The difference (log(SFR(Pa α )-SFR( Prospector )) is −0.09 ± 0.04 dex at 10 ^10−11 M _⊙ . We also measure the empirical relation between Paschen- α luminosity and rest-frame H- band magnitude and find that the scatter is only 0.04 dex lower than that of the SFR– M * relation and is much lower than the systematic differences among relations in the literature due to various methods of converting observed measurements to physical properties. We additionally identify examples of sources—that, with standard cutoffs via the UVJ diagram, would be deemed quiescent—with significant (log(sSFR)> −11 yr ^−1 ), typically extended, Paschen- α emission. Our results may be indicative of the potential unification of methods used to derive the SFS with careful selection of star-forming galaxies and independent SFR and stellar mass indicators.

We present the construction of a deep multiwavelength point-spread-function-matched photometric catalog in the Ultra-Deep Survey (UDS) field following the final UKIDSS UDS release. The catalog includes photometry in 24 filters, from the MegaCam- uS 0.38 μ m band to the Spitzer-IRAC 8 μ m band, over ∼0.9 deg ^2 and with a 5 σ depth of 25.3 AB in the K -band detection image. The catalog, containing ≈188,564 (136,235) galaxies at 0.2 < z < 8.0 with stellar mass $\mathrm{log}({M}_{* }/{M}_{\odot })\gt 8$ and K -band total magnitude K < 25.2 (24.3) AB, enables a range of extragalactic studies. We also provide photometric redshifts, corresponding redshift probability distributions, and rest-frame absolute magnitudes and colors derived using the template-fitting code eazy-py . Photometric redshift errors are less than 3%−4% at z < 4 across the full brightness range in the K band and stellar mass range $8\lt \mathrm{log}({M}_{* }/{M}_{\odot })\lt 12$ . Stellar population properties (e.g., stellar mass, star formation rate, dust extinction) are derived from the modeling of the spectral energy distributions using the codes FAST and Dense Basis.

The current and upcoming large data volume galaxy surveys require the use of machine-learning techniques to maximize their scientific return. This study explores the use of Self-Organizing Maps (SOMs) to estimate galaxy parameters with a focus on handling cases of missing data and providing realistic probability distribution functions for the parameters. We train an SOM with a simulated mass-limited lightcone assuming a ugrizY JHK _s +IRAC data set, mimicking the Hyper Suprime-Cam Deep joint data set. For parameter estimation, we derive SOM likelihood surfaces considering photometric errors to derive total (statistical and systematic) uncertainties. We explore the effects of missing data, including which bands are particularly critical to the accuracy of the derived parameters. We demonstrate that the parameter recovery is significantly better when the missing bands are “filled in” rather than if they are completely omitted. We propose a practical method for such recovery of missing data.

The resolved mass assembly of Milky Way–mass galaxies has been previously studied in simulations, the local Universe, and at higher redshifts using infrared (IR) light profiles. To better characterize the mass assembly of Milky Way analogs (MWAs), as well as their changes in star formation rate (SFR) and color gradients, we construct resolved stellar mass and SFR maps of MWA progenitors selected with abundance matching techniques up to z ∼2 using deep, multiwavelength imaging data from the Hubble Frontier Fields. Our results using stellar mass profiles agree well with previous studies that utilize IR light profiles, showing that the inner 2 kpc of the galaxies and the regions beyond 2 kpc exhibit similar rates of stellar mass growth. This indicates the progenitors of MWAs from z ∼ 2 to the present do not preferentially grow their bulges or their disks. The evolution of the SFR profiles indicates a greater decrease in SFR density in the inner regions versus the outer regions. Sérsic parameters indicate modest growth in the central regions at lower redshifts, perhaps indicating slight bulge growth. However, the Sérsic index does not rise above n ∼ 2 until z < 0.5, meaning these galaxies are still disk-dominated systems. We find that the half-mass radii of the MWA progenitors increase between 1.5 < z < 2, but remain constant at later epochs ( z < 1.5). This implies mild bulge growth since z ∼ 2 in MWA progenitors, in line with previous MWA mass assembly studies.

The James Webb Space Telescope is revealing a new population of dust-reddened broad-line active galactic nuclei (AGN) at redshifts z ≳ 5. Here we present deep NIRSpec/Prism spectroscopy from the Cycle 1 Treasury program Ultradeep NIRSpec and NIRCam ObserVations before the Epoch of Reionization (UNCOVER) of 15 AGN candidates selected to be compact, with red continua in the rest-frame optical but with blue slopes in the UV. From NIRCam photometry alone, they could have been dominated by dusty star formation or an AGN. Here we show that the majority of the compact red sources in UNCOVER are dust-reddened AGN: 60% show definitive evidence for broad-line H α with a FWHM > 2000 km s ^−1 , 20% of the current data are inconclusive, and 20% are brown dwarf stars. We propose an updated photometric criterion to select red z > 5 AGN that excludes brown dwarfs and is expected to yield >80% AGN. Remarkably, among all z _phot > 5 galaxies with F277W – F444W > 1 in UNCOVER at least 33% are AGN regardless of compactness, climbing to at least 80% AGN for sources with F277W – F444W > 1.6. The confirmed AGN have black hole masses of 10 ^7 –10 ^9 M _⊙ . While their UV luminosities (−16 > M _UV > −20 AB mag) are low compared to UV-selected AGN at these epochs, consistent with percent-level scattered AGN light or low levels of unobscured star formation, the inferred bolometric luminosities are typical of 10 ^7 –10 ^9 M _⊙ black holes radiating at ∼10%–40% the Eddington limit. The number densities are surprisingly high at ∼10 ^−5 Mpc ^−3 mag ^−1 , 100 times more common than the faintest UV-selected quasars, while accounting for ∼1% of the UV-selected galaxies. While their UV faintness suggests they may not contribute strongly to reionization, their ubiquity poses challenges to models of black hole growth.

We report JWST/NIRSpec spectra of three distant T-type brown dwarfs identified in the Ultradeep NIRSpec and NIRCam ObserVations before the Epoch of Reionization (UNCOVER) survey of the Abell 2744 lensing field. One source was previously reported as a candidate T dwarf on the basis of NIRCam photometry, while two sources were initially identified as candidate active galactic nuclei. Low-resolution 1–5 μ m spectra confirm the presence of molecular features consistent with T dwarf atmospheres, and comparison to spectral standards infers classifications of sdT1, T6, and T8–T9. The warmest source, UNCOVER-BD-1, shows evidence of subsolar metallicity, and atmosphere model fits indicate T _eff = 1300 K and [M/H] ∼ −1.0, making this one of the few spectroscopically confirmed T subdwarfs known. The coldest source, UNCOVER-BD-3, is near the T/Y dwarf boundary with T _eff = 550 K, and our analysis indicates the presence of PH _3 in the 3–5 μ m region, favored over CO _2 and a possible indicator of subsolar metallicity. We estimate distances of 0.9–4.5 kpc from the Galactic midplane, making these the most distant brown dwarfs with spectroscopic confirmation. Population simulations indicate high probabilities of membership in the Galactic thick disk for two of these brown dwarfs, and potential halo membership for UNCOVER-BD-1. Our simulations indicate that there are approximately 5 T dwarfs and 1–2 L dwarfs in the Abell 2744 field down to F444W = 30 AB mag, roughly one-third of which are thick disk members. These results highlight the utility of deep JWST/NIRSpec spectroscopy for identifying and characterizing the oldest metal-poor brown dwarfs in the Milky Way.

Observations of high-redshift galaxies provide a critical direct test to the theories of early galaxy formation, yet to date, only three have been spectroscopically confirmed at z > 12. Due to strong gravitational lensing over a wide area, the galaxy cluster field A2744 is ideal for searching for the earliest galaxies. Here we present JWST/NIRSpec observations of two galaxies: a robust detection at ${z}_{\mathrm{spec}}={12.393}_{-0.001}^{+0.004}$ , and a plausible candidate at ${z}_{\mathrm{spec}}={13.079}_{-0.001}^{+0.013}$ . The galaxies are discovered in JWST/NIRCam imaging and their distances are inferred with JWST/NIRSpec spectroscopy, all from the JWST Cycle 1 UNCOVER Treasury survey. Detailed stellar population modeling using JWST NIRCam and NIRSpec data corroborates the primeval characteristics of these galaxies: low mass (∼10 ^8 M _⊙ ), young, rapidly assembling, metal-poor, and star-forming. Interestingly, both galaxies are spatially resolved, having lensing-corrected rest-UV effective radii on the order of 300–400 pc, which are notably larger than other spectroscopically confirmed systems at similar redshifts. The observed dynamic range of z ≳ 10 sizes spans over 1 order of magnitude, implying a significant scatter in the size–mass relation at early times. Deep into the epoch of reionization, these discoveries elucidate the emergence of the first galaxies.

Deep observations with the James Webb Space Telescope (JWST) have revealed an emerging population of red pointlike sources that could provide a link between the postulated supermassive black hole seeds and observed quasars. In this work, we present a JWST/NIRSpec spectrum from the JWST Cycle 1 UNCOVER Treasury survey of a massive accreting black hole at z = 8.50 displaying a clear broad-line component as inferred from the H β line with FWHM = 3439 ± 413 km s ^−1 , typical of the broad-line region of an active galactic nucleus (AGN). The AGN nature of this object is further supported by high ionization, as inferred from emission lines, and a point-source morphology. We compute a black hole mass of ${\mathrm{log}}_{10}({M}_{\mathrm{BH}}/{M}_{\odot })=8.17\pm 0.42$ and a bolometric luminosity of L _bol ∼ 6.6 × 10 ^45 erg s ^−1 . These values imply that our object is accreting at ∼40% of the Eddington limit. Detailed modeling of the spectral energy distribution in the optical and near-infrared, together with constraints from ALMA, indicate an upper limit on the stellar mass of ${\mathrm{log}}_{10}({M}_{* }/{M}_{\odot })\lt 8.7$ , which would lead to an unprecedented ratio of black hole to host mass of at least ∼30%. This is orders of magnitude higher compared to the local QSOs but consistent with recent AGN studies at high redshift with JWST. This finding suggests that a nonnegligible fraction of supermassive black holes either started out from massive seeds and/or grew at a super-Eddington rate at high redshift. Given the predicted number densities of high- z faint AGN, future NIRSpec observations of larger samples will allow us to further investigate galaxy–black hole coevolution in the early Universe.

The James Webb Space Telescope is now detecting early black holes (BHs) as they transition from “seeds” to supermassive BHs. Recently, Bogdan et al. reported the detection of an X-ray luminous supermassive BH, UHZ-1, with a photometric redshift at z > 10. Such an extreme source at this very high redshift provides new insights on seeding and growth models for BHs given the short time available for formation and growth. Harnessing the exquisite sensitivity of JWST/NIRSpec, here we report the spectroscopic confirmation of UHZ-1 at z = 10.073 ± 0.002. We find that the NIRSpec/Prism spectrum is typical of recently discovered z ≈ 10 galaxies, characterized primarily by star formation features. We see no clear evidence of the powerful X-ray source in the rest-frame UV/optical spectrum, which may suggest heavy obscuration of the central BH, in line with the Compton-thick column density measured in the X-rays. We perform a stellar population fit simultaneously to the new NIRSpec spectroscopy and previously available photometry. The fit yields a stellar-mass estimate for the host galaxy that is significantly better constrained than prior photometric estimates ( ${M}_{\star }\sim {1.4}_{-0.4}^{+0.3}\times {10}^{8}$ M _⊙ ). Given the predicted BH mass ( M _BH ∼ 10 ^7 –10 ^8 M _⊙ ), the resulting ratio of M _BH / M _⋆ remains 2 to 3 orders of magnitude higher than local values, thus lending support to the heavy seeding channel for the formation of supermassive BHs within the first billion years of cosmic evolution.

We report ALMA detections of [C ii ] and a dust continuum in Az9, a multiply imaged galaxy behind the Frontier Field cluster MACS J0717.5+3745. The bright [C ii ] emission line provides a spectroscopic redshift of z = 4.274. This strongly lensed ( μ = 7 ± 1) galaxy has an intrinsic stellar mass of only 2 × 10 ^9 M _⊙ and a total star formation rate of 26 M _⊙ yr ^−1 (∼80% of which is dust-obscured). Using public magnification maps, we reconstruct the [C ii ] emission in the source plane to reveal a stable, rotation-dominated disk with V / σ = 5.3, which is >2× higher than predicted from simulations for similarly high-redshift, low-mass galaxies. In the source plane, the [C ii ] disk has a half-light radius of 1.8 kpc and, along with the dust, is spatially offset from the peak of the stellar light by 1.4 kpc. Az9 is not deficient in [C ii ]; L _[C _II _] / L _IR = 0.0027, consistent with local and high-redshift normal star-forming galaxies. While dust-obscured star formation is expected to dominate in higher-mass galaxies, such a large reservoir of dust and gas in a lower-mass disk galaxy 1.4 Gyr after the Big Bang challenges our picture of early galaxy evolution. Furthermore, the prevalence of such low-mass dusty galaxies has important implications for the selection of the highest-redshift dropout galaxies with JWST. As one of the lowest stellar mass galaxies at z > 4 to be detected in a dust continuum and [C ii ], Az9 is an excellent laboratory in which to study early dust enrichment in the interstellar medium.

We present the spectroscopic confirmation of a protocluster at z = 7.88 behind the galaxy cluster Abell 2744 (hereafter A2744-z7p9OD). Using JWST NIRSpec, we find seven galaxies within a projected radius of 60 kpc. Although the galaxies reside in an overdensity around ≳20× greater than a random volume, they do not show strong Ly α emission. We place 2 σ upper limits on the rest-frame equivalent width 0.45 (68% C i ). Using an empirical M _UV – M _halo relation for individual galaxies, we estimate that the total halo mass of the system is ≳4 × 10 ^11 M _⊙ . Likewise, the line-of-sight velocity dispersion is estimated to be 1100 ± 200 km s ^−1 . Using an empirical relation, we estimate the present-day halo mass of A2744-z7p9OD to be ∼2 × 10 ^15 M _⊙ , comparable to the Coma cluster. A2744-z7p9OD is the highest redshift spectroscopically confirmed protocluster to date, demonstrating the power of JWST to investigate the connection between dark-matter halo assembly and galaxy formation at very early times with medium-deep observations at

We use the GLASS-JWST Early Release Science NIRCam parallel observations to provide a first view of the UV continuum properties of NIRCam/F444W selected galaxies at 4 < z < 7. By combining multiwavelength NIRCam observations, we constrain the UV continuum slope for a sample of 401 galaxies with stringent quality controls. We find that >99% of the galaxies are blue star-forming galaxies with very low levels of dust ( Av _β ∼ 0.01 ± 0.33). We find no statistically significant correlation for UV slope with redshift or UV magnitude. However, we find that in general galaxies at higher redshifts and fainter UV magnitudes have steeper UV slopes. We find a statistically significant correlation for UV slope with stellar mass, with galaxies with higher stellar mass showing shallower UV slopes. Individual fits to some of our galaxies reach the bluest UV slopes of β ∼ −3.1 allowed by stellar population models used in this analysis. Therefore, it is likely that stellar population models with a higher amount of Lyman continuum leakage, active galactic nucleus effects, and/or Population III contributions are required to accurately reproduce the rest-UV and optical properties of some of our bluest galaxies. This dust-free early view confirms that our current cosmological understanding of gradual mass + dust buildup of galaxies with cosmic time is largely accurate to describe the ∼0.7–1.5 Gyr age window of the universe. The abundance of a large population of UV faint dust-poor systems may point to a dominance of low-mass galaxies at z > 6 playing a vital role in cosmic reionization.

How passive galaxies form, and the physical mechanisms which prevent star formation over long timescales, are some of the most outstanding questions in understanding galaxy evolution. The properties of quiescent galaxies over cosmic time provide crucial information to identify the quenching mechanisms. Passive galaxies have been confirmed and studied out to z ∼ 4, but all of these studies have been limited to massive systems (mostly with $\mathrm{log}({M}_{\mathrm{star}}/{M}_{\odot })\gt 10.8$ ). Using JWST-NIRISS grism slitless spectroscopic data from the GLASS-JWST Early Release Science program, we present spectroscopic confirmation of two quiescent galaxies at ${z}_{\mathrm{spec}}={2.650}_{-0.006}^{+0.004}$ and ${z}_{\mathrm{spec}}={2.433}_{-0.016}^{+0.032}$ (3 σ errors) with stellar masses of $\mathrm{log}({M}_{\mathrm{star}}/{M}_{\odot })={10.59}_{-0.05}^{+0.11}$ and $\mathrm{log}({M}_{\mathrm{star}}/{M}_{\odot })={10.07}_{-0.03}^{+0.06}$ (corrected for magnification factors of μ = 2.0 and μ = 2.1, respectively). The latter represents the first spectroscopic confirmation of the existence of low-mass quiescent galaxies at cosmic noon, showcasing the power of JWST to identify and characterize this enigmatic population.

In 2022 November, the James Webb Space Telescope (JWST) returned deep near-infrared images of A2744—a powerful lensing cluster capable of magnifying distant, incipient galaxies beyond it. Together with existing Hubble Space Telescope (HST) imaging, this publicly available data set opens a fundamentally new discovery space to understand the remaining mysteries of the formation and evolution of galaxies across cosmic time. In this work, we detect and measure some 60,000 objects across the 49 arcmin ^2 JWST footprint down to a 5 σ limiting magnitude of ∼30 mag in 0.″32 apertures. Photometry is performed using circular apertures on images matched to the point-spread function (PSF) of the reddest NIRCam broad band, F444W, and cleaned of bright cluster galaxies and the related intracluster light. To give an impression of the photometric performance, we measure photometric redshifts and achieve a σ _NMAD ≈ 0.03 based on known, but relatively small, spectroscopic samples. With this paper, we publicly release our HST and JWST PSF-matched photometric catalog with optimally assigned aperture sizes for easy use, along with single aperture catalogs, photometric redshifts, rest-frame colors, and individual magnification estimates. These catalogs will set the stage for efficient and deep spectroscopic follow up of some of the first JWST-selected samples in summer of 2023.

The recent UNCOVER survey with the James Webb Space Telescope (JWST) exploits the nearby cluster A2744 to create the deepest view of our Universe to date by leveraging strong gravitational lensing. In this work, we perform photometric fitting of more than 50,000 robustly detected sources out to z ∼ 15. We show the redshift evolution of stellar ages, star formation rates, and rest-frame colors across the full range of 0.2 ≲ z ≲ 15. The galaxy properties are inferred using the Prospector Bayesian inference framework using informative Prospector - β priors on the masses and star formation histories to produce joint redshift and stellar populations posteriors. Additionally, lensing magnification is performed on the fly to ensure consistency with the scale-dependent priors. We show that this approach produces excellent photometric redshifts with σ _NMAD ∼ 0.03, of a similar quality to the established photometric redshift code EAzY . In line with the open-source scientific objective of this Treasury survey, we publicly release the stellar population catalog with this paper, derived from our photometric catalog adapting aperture sizes based on source profiles. This release (the catalog and all related documentation are accessible via the UNCOVER survey web page: https://jwst-uncover.github.io/DR2.html#SPSCatalogs with a copy deposited to Zenodo at doi: https://doi.org/10.5281/zenodo.8401181 ) includes posterior moments, maximum likelihood spectra, star formation histories, and full posterior distributions, offering a rich data set to explore the processes governing galaxy formation and evolution over a parameter space now accessible by JWST.

We use CEERS JWST/NIRCam imaging to measure rest-frame near-IR light profiles of 435 M _⋆ > 10 ^10 M _⊙ galaxies in the redshift range of 0.5 < z < 2.3. We compare the resulting rest-frame 1.5–2 μ m half-light radii ( R _NIR ) with stellar half-mass radii ( ${R}_{{{M}}_{\star }}$ ) derived with multicolor light profiles from CANDELS Hubble Space Telescope imaging. In general agreement with previous work, we find that R _NIR and ${R}_{{{M}}_{\star }}$ are up to 40% smaller than the rest-frame optical half-light radius R _opt . The agreement between R _NIR and ${R}_{{{M}}_{\star }}$ is excellent, with a negligible systematic offset ( 10 ^11 M _⊙ ) quiescent galaxies between z = 0.5 and z = 2.3, again comparing R _opt , ${R}_{{{M}}_{\star }}$ , and ${R}_{{{M}}_{\star },3{\rm{D}}}$ . We conclude that the main tenets of the evolution of the size narrative established over the past 20 yr, based on rest-frame optical light profile analysis, still hold in the era of JWST/NIRCam observations in the rest-frame near-IR.

We present new Spitzer Infrared Array Camera (IRAC) 3.6 and 4.5 μ m mosaics of three fields, E-COSMOS, DEEP2-F3, and ELAIS-N1. Our mosaics include both new IRAC observations as well as reprocessed archival data in these fields. These fields are part of the HSC-Deep grizy survey and have a wealth of additional ancillary data. The addition of these new IRAC mosaics is critical in allowing for improved photometric redshifts and stellar population parameters at cosmic noon and earlier epochs. The total area mapped by this work is ∼17 deg ^2 with a mean integration time of ≈1200s, providing a median 5 σ depth of 23.7(23.3) at 3.6(4.5) μ m in AB. We perform SExtractor photometry both on the combined mosaics as well as the single-epoch mosaics taken ≈6 months apart. The resultant IRAC number counts show good agreement with previous studies. In combination with the wealth of existing and upcoming spectrophotometric data in these fields, our IRAC mosaics will enable a wide range of galactic evolution and AGN studies. With that goal in mind, we make the combined IRAC mosaics and coverage maps of these three fields publicly available.

Recent JWST/NIRCam imaging taken for the ultra-deep UNCOVER program reveals a very red dropout object at z _phot ≃ 7.6, triply imaged by the galaxy cluster A2744 ( z _d = 0.308). All three images are very compact, i.e., unresolved, with a delensed size upper limit of r _e ≲ 35 pc. The images have apparent magnitudes of m _F444W ∼ 25−26 AB, and the magnification-corrected absolute UV magnitude of the source is M _UV,1450 = −16.81 ± 0.09. From the sum of observed fluxes and from a spectral energy distribution (SED) analysis, we obtain estimates of the bolometric luminosities of the source of L _bol ≳ 10 ^43 erg s ^−1 and L _bol ∼ 10 ^44 –10 ^46 erg s ^−1 , respectively. Based on its compact, point-like appearance, its position in color–color space, and the SED analysis, we tentatively conclude that this object is a UV-faint dust-obscured quasar-like object, i.e., an active galactic nucleus at high redshift. We also discuss other alternative origins for the object’s emission features, including a massive star cluster, Population III, supermassive, or dark stars, or a direct-collapse black hole. Although populations of red galaxies at similar photometric redshifts have been detected with JWST, this object is unique in that its high-redshift nature is corroborated geometrically by lensing, that it is unresolved despite being magnified—and thus intrinsically even more compact—and that it occupies notably distinct regions in both size–luminosity and color–color space. Planned UNCOVER JWST/NIRSpec observations, scheduled in Cycle 1, will enable a more detailed analysis of this object.

We present a new rest-frame color–color selection method using synthetic u _s − g _s and g _s − i _s , ( ugi ) _s colors to identify star-forming and quiescent galaxies. Our method is similar to the widely used U − V versus V − J ( UVJ ) diagram. However, UVJ suffers known systematics. Spectroscopic campaigns have shown that UVJ -selected quiescent samples at z ≳ 3 include ∼10%–30% contamination from galaxies with dust-obscured star formation and strong emission lines. Moreover, at z > 3, UVJ colors are extrapolated because the rest-frame band shifts beyond the coverage of the deepest bandpasses at 3, and can be applied to galaxies in the JWST era. We apply ( ugi ) _s selection to galaxies at 0.5 < z < 6 from the (observed) 3D-HST and UltraVISTA catalogs, and to the (simulated) JAGUAR catalogs. We show that extrapolation can affect ( V − J ) _0 color by up to 1 mag, but changes ${({g}_{s}-{i}_{s})}_{0}$ color by ≤0.2 mag, even at z ≃ 6. While ( ugi ) _s -selected quiescent samples are comparable to UVJ in completeness (both achieve ∼85%–90% at z = 3–3.5), ( ugi ) _s reduces contamination in quiescent samples by nearly a factor of 2, from ≃35% to ≃17% at z = 3, and from ≃60% to ≃33% at z = 6. This leads to improvements in the true-to-false-positive ratio (TP/FP), where we find TP/FP ≳2.2 for ( ugi ) _s at z ≃ 3.5 − 6, compared to TP/FP < 1 for UVJ -selected samples. This indicates that contaminants will outnumber true quiescent galaxies in UVJ at these redshifts, while ( ugi ) _s will provide higher-fidelity samples.