Search

JWST has revealed an abundance of compact, red objects at $z\approx5-8$ dubbed "little red dots" (LRDs), whose SEDs display a faint blue UV continuum followed by a steep rise in the optical. Despite extensive study of their characteristic V-shaped SEDs, the nature of LRDs remains unknown. We present a new analysis of the NIRSpec/PRISM spectrum of A2744-QSO1, a triply imaged LRD at $z=7.04$ from the UNCOVER survey. The spectrum shows a strong Balmer break and broad Balmer emission lines, both of which are difficult to explain with models invoking exclusively AGN or stellar contributions. Our fiducial model decomposes the spectrum into a post-starburst galaxy dominating the UV-optical continuum and a reddened AGN being sub-dominant at all wavelength and contributing at $\sim20\%$ level. However, our most credible model infers a stellar mass of $M_\star\approx 4\times10^9\,\mathrm{M_\odot}$ within a radius of $r_\mathrm{e}<30\,$pc, driving its central density to the highest among observations to date. This high central density could be explained if A2744-QSO-1 is the early-forming core of a modern-day massive elliptical galaxy that later puffed up via the inside-out growth channel. The models also necessitate an unusually steep dust law to preserve the strong break strength, though this steepness may be explained by a deficit of large dust grains. It is also probable that these challenges reflect our ignorance of A2744-QSO1's true nature. Future variability and reverberation mapping studies could help disentangle the galaxy and AGN contribution to the continuum, and deeper redder observations could also unveil the dust properties in LRDs., Comment: 19 pages, 7 figures, 2 tables. Submitted to ApJ. Comments are welcome

We present the formation histories of 19 massive ($\gtrsim3\times10^{10}\text{M}_\odot$) quiescent galaxy candidates at $z\sim3.0-4.5$ observed using JWST/NIRSpec. This completes the spectroscopic confirmation of the 24 $K$-selected quiescent galaxy sample from the ZFOURGE and 3DHST surveys \citep{Schreiber2018}. Utilizing Prism $1-5\mu$m spectroscopy, we confirm that all 12 sources that eluded confirmation by ground-based spectroscopy lie at $z>3$, resulting in a spectroscopically confirmed number density of $\sim1.4\times10^{-5}\text{Mpc}^{-3}$ between $z\sim3-4$. Rest-frame $U-V$ vs $V-J$ color selections show high effectiveness in identifying quiescent galaxies, with a purity of $\sim90\%$. Our analysis shows that parametric star-formation histories (SFHs) from FAST++ and binned SFHs from Prospector on average yield consistent results, revealing diverse formation and quenching times. The oldest galaxy formed $\sim6\times10^{10}\text{M}_\odot$ by $z\sim10$ and has been quiescent for over 1 Gyr at $z\sim3.2$. We detect two galaxies with ongoing star formation and six with active galactic nuclei (AGN). We demonstrate that the choice of stellar population models, stellar libraries, wavelength range, and nebular or AGN contributions does not significantly affect the derived average SFHs of the galaxies. The assumed SFH prior, however, influences the star formation rate at early times, where spectral diagnostic power is limited. Simulated $z\sim3$ quiescent galaxies from IllustrisTNG, SHARK, and Magneticum broadly match the average SFHs of the observed sample but struggle to capture the full diversity, particularly at early stages. Our results emphasize the need for mechanisms that rapidly build stellar mass and quench star formation within the first billion years of the Universe., Comment: Submitted to ApJ. Comments welcome

We present the PANORAMIC survey, a pure parallel extragalactic imaging program with NIRCam observed during JWST Cycle 1. The survey obtained $\sim$530 sq arcmin of NIRCam imaging from 1-5$\mu$m, totaling $\sim$192 hours of science integration time. This represents the largest on-sky time investment of any Cycle 1 GO extragalactic NIRCam imaging program by nearly a factor of 2. The survey includes $\sim$432 sq arcmin of novel sky area not yet observed with JWST using at least $6$ NIRCam broad-band filters, increasing the existing area covered by similar Cycle 1 data by $\sim$60%. 70 square arcmin was also covered by a 7th filter (F410M). A fraction of PANORAMIC data ($\sim$200 sq arcmin) was obtained in or around extragalactic deep-fields, enhancing their legacy value. Pure parallel observing naturally creates a wedding cake survey with both wide and ultra-deep tiers, with 5$\sigma$ point source depths at F444W ranging from 27.8-29.4 (ABmag), and with minimized cosmic variance. The 6+ filter observing setup yields remarkably good photometric redshift performance, achieving similar median scatter and outlier fraction as CANDELS ($\sigma_{\rm NMAD}\sim0.07$; $\eta\sim0.2$), which enables a wealth of science across redshift without the need for followup or ancillary data. We overview the proposed survey, the data obtained as part of this program, and document the science-ready data products in the first data release. PANORAMIC has delivered wide-area and deep imaging with excellent photometric performance, demonstrating that pure parallel observations with JWST are a highly efficient observing mode that is key to acquiring a complete picture of galaxy evolution from rare bright galaxies to fainter, more abundant sources at all redshifts., Comment: Submitted to AAS Journals; comments welcome. Initial data release available at https://panoramic-jwst.github.io/

Dwarf galaxies hold the key to crucial frontiers of astrophysics, however, their faintness renders spectroscopy challenging. Here we present the JWST Cycle 2 survey, All the Little Things (ALT, PID 3516), which is designed to seek late-forming Pop III stars and the drivers of reionization at $z\sim6-7$. ALT has acquired the deepest NIRCam grism spectroscopy yet (7-27 hr), at JWST's most sensitive wavelengths (3-4 $\mu$m), covering the powerful lensing cluster Abell 2744. Over the same 30 arcmin$^2$, ALT's ultra-deep F070W+F090W imaging ($\sim$30 mag) enables selection of very faint sources at $z>6$. We demonstrate the success of ALT's novel ``butterfly" mosaic to solve spectral confusion and contamination, and introduce the ``Allegro" method for emission line identification. By collecting spectra for every source in the field of view, ALT has measured precise ($R\sim1600$) redshifts for 1630 sources at $z=0.2-8.5$. This includes one of the largest samples of distant dwarf galaxies: [1015, 475, 50] sources less massive than the SMC, Fornax, and Sculptor with $\log(M_{*}/M_{\odot})<$[8.5, 7.5, 6.5]. We showcase ALT's discovery space with: (i) spatially resolved spectra of lensed clumps in galaxies as faint as $M_{\rm{UV}}\sim-15$; (ii) large-scale clustering -- overdensities at $z$=[2.50, 2.58, 3.97, 4.30, 5.66, 5.77, 6.33] hosting massive galaxies with striking Balmer breaks; (iii) small-scale clustering -- a system of satellites around a Milky Way analog at $z\sim6$; (iv) spectroscopically confirmed multiple images that help constrain the lensing model underlying all science in this legacy field; (v) sensitive star-formation maps based on dust-insensitive tracers such as Pa$\alpha$; (vi) direct spectroscopic discovery of rare sources such as AGN with ionized outflows. These results provide a powerful proof of concept for how grism surveys maximize the potential of strong lensing fields., Comment: Submitted to the Open Journal of Astrophysics. Figs. 6 and 10 illustrate the quality of the spectra and imaging, while Fig. 12 summarizes the yield of the survey. Comments warmly welcomed and greatly appreciated. The ALT DR1 catalog is available at https://zenodo.org/records/13871850

JWST has revealed diverse new populations of high-redshift ($z\sim4-11$) AGN and extreme star-forming galaxies that challenge current models. In this paper, we use rest-frame UV emission-line diagnostics to identify AGN candidates and other exceptional ionizing sources, complementing previous studies predominantly focused on broad-line AGN. In this paper, we use rest-frame UV emission-line diagnostics to identify AGN candidates and other exceptional ionizing sources, complementing previous studies predominantly focused on broad-line AGN. From a parent sample of 205 $\mathrm{z_{spec}}>3$ UNCOVER galaxies with NIRSpec/PRISM follow-up, we identify 12 C IV, He II, and C III] emitters. Leveraging the combined rest-optical and UV coverage of PRISM, we limit the emission-line model space using the sample's [O III]/H$\beta$ distribution, significantly decreasing the overlap between AGN and star-formation models in the UV diagnostics. We then find that the five He II emitters are the strongest AGN candidates, with further support from two [Ne V] detections and one X-ray detection from Chandra. We cannot robustly quantify the AGN fraction in this sample, but we note that close to 20% of $\mathrm{M_{*}>2\times10^{9}\,M_{\odot}}$ parent sample galaxies are AGN candidates. The lower-mass line emitters, which are consistent with both AGN and star-forming photoionization models, have more compact sizes and higher specific star formation rates than the parent sample. Higher-resolution and deeper data on these UV line emitters should provide much stronger constraints on the obscured AGN fraction at $z > 3$., Comment: Submitted to ApJ

We explore the physical properties of five massive quiescent galaxies at $z\sim2.5$, revealing the presence of non-negligible dust reservoirs. JWST NIRSpec observations were obtained for each target, finding no significant line emission; multiple star formation tracers independently place upper limits between $0.1-10~M_\odot / \mathrm{yr}$. Spectral energy distribution modeling with Prospector infers stellar masses between $\log_{10}[M / M_\odot] \sim 10-11$ and stellar mass-weighted ages between $1-2$ Gyr. The inferred mass-weighted effective radii ($r_{eff}\sim 0.4-1.4$ kpc) and inner $1$ kpc stellar surface densities ($\log_{10}[\Sigma / M_\odot \mathrm{kpc}^2 ]\gtrsim 9$) are typical of quiescent galaxies at $z \gtrsim 2$. The galaxies display negative color gradients (redder core and bluer outskirts); for one galaxy, this effect results from a dusty core, while for the others it may be evidence of an "inside-out" growth process. Unlike local quiescent galaxies, we identify significant reddening in these typical cosmic noon passive galaxies; all but one require $A_V \gtrsim 0.4$. This finding is in qualitative agreement with previous studies but our deep 20-band NIRCam imaging is able to significantly suppress the dust-age degeneracy and confidently determine that these galaxies are reddened. We speculate about the physical effects that may drive the decline in dust content in quiescent galaxies over cosmic time., Comment: 18 pages, 8 figures, submitted to ApJ

We present the Red Unknowns: Bright Infrared Extragalactic Survey (RUBIES), providing JWST/NIRSpec spectroscopy of red sources selected across ~150 arcmin$^2$ from public JWST/NIRCam imaging in the UDS and EGS fields. RUBIES novel observing strategy offers a well-quantified selection function: the survey is optimised to reach high (>70%) completeness for bright and red (F150W-F444W>2) sources that are very rare. To place these rare sources in context, we simultaneously observe a reference sample of the 23$ using only the G395M disperser. The RUBIES data reveal a highly diverse population of red sources that span a broad redshift range ($z_{spec}\sim1-9$), with photometric redshift scatter and outlier fraction that are 3 times higher than for similarly bright sources that are less red. This diversity is not apparent from the photometric SEDs. Only spectroscopy reveals that the SEDs encompass a mixture of galaxies with dust-obscured star formation, extreme line emission, a lack of star formation indicating early quenching, and luminous active galactic nuclei. As a first demonstration of our broader selection function we compare the stellar masses and rest-frame U-V colours of the red sources and our reference sample: red sources are typically more massive ($M_*\sim10^{10-11.5} M_\odot$) across all redshifts. However, we find that the most massive systems span a wide range in U-V colour. We describe our data reduction procedure and data quality, and publicly release the reduced RUBIES data and vetted spectroscopic redshifts of the first half of the survey through the DJA., Comment: 21 pages, 16 figures; submitted to A&A

We report the spectroscopic discovery of a massive quiescent galaxy at $z_{\rm spec}=7.29\pm0.01$, just $\sim700\,$Myr after the Big Bang. RUBIES-UDS-QG-z7 was selected from public JWST/NIRCam and MIRI imaging from the PRIMER survey and observed with JWST/NIRSpec as part of RUBIES. The NIRSpec/PRISM spectrum reveals one of the strongest Balmer breaks observed thus far at $z>6$, no emission lines, but tentative Balmer and Ca absorption features, as well as a Lyman break. Simultaneous modeling of the NIRSpec/PRISM spectrum and NIRCam and MIRI photometry (spanning $0.9-18\,\mu$m) shows that the galaxy formed a stellar mass of log$(M_*/M_\odot)=10.23^{+0.04}_{-0.04}$ in a rapid $\sim 100-200\,$Myr burst of star formation at $z\sim8-9$, and ceased forming stars by $z\sim8$ resulting in $\log \rm{sSFR/yr}^{-1}<-10$. We measure a small physical size of $209_{-24}^{+33}\,{\rm pc}$, which implies a high stellar mass surface density within the effective radius of $\log(\Sigma_{*,\rm e}/{\rm M_\odot\,kpc}^{-2})=10.85_{-0.12}^{+0.11}$ comparable to the densities measured in quiescent galaxies at $z\sim2-5$. The 3D stellar mass density profile of RUBIES-UDS-QG-z7 is remarkably similar to the central densities of local massive ellipticals, suggesting that at least some of their cores may have already been in place at $z>7$. The discovery of RUBIES-UDS-QG-z7 has strong implications for galaxy formation models: the estimated number density of quiescent galaxies at $z\sim7$ is $>100\times$ larger than predicted from any model to date, indicating that quiescent galaxies have formed earlier than previously expected., Comment: 21 pages, 7 figures, submitted to ApJ

Early JWST studies found an apparent population of massive, compact galaxies at redshifts $z\gtrsim7$. Recently three of these galaxies were shown to have prominent Balmer breaks, demonstrating that their light at $\lambda_{\rm rest} \sim 3500$ $\r{A}$ is dominated by a stellar population that is relatively old ($\sim$200 Myr). All three also have broad H$\beta$ emission with $\sigma > 1000 \,\rm km s^{-1}$, a common feature of such `little red dots'. From S\'ersic profile fits to the NIRCam images in F200W we find that the stellar light of galaxies is extremely compact: the galaxies have half-light radii of $r_{\rm e}\sim$ 100 pc, in the regime of ultra compact dwarfs in the nearby Universe. Their masses are uncertain, as they depend on the contribution of possible light from an AGN to the flux at $\lambda_{\rm rest}>5000$ $\r{A}$. If the AGN contribution is low beyond the Balmer break region, the masses are $M_* \sim 10^{10}-10^{11}\mathrm{M}_{\odot}$, and the central densities are higher than those of any other known galaxy population by an order of magnitude. Interestingly, the implied velocity dispersions of $\sim$1500 kms$^{-1}$ are in very good agreement with the measured H$\beta$ line widths. We suggest that some of the broad lines in `little red dots' are not due to AGNs but simply reflect the kinematics of the galaxies, and speculate that the galaxies are observed in a short-lived phase where the central densities are much higher than at later times. We stress, however, that the canonical interpretation of AGNs causing the broad H$\beta$ lines also remains viable.

We present the design and observations of low resolution JWST/NIRSpec PRISM spectroscopy from the Ultradeep NIRSpec and NIRCam ObserVations before the Epoch of Reionization (UNCOVER) Cycle 1 JWST Treasury program. Targets are selected using JWST/NIRCam photometry from UNCOVER and other programs, and cover a wide range of categories and redshifts to ensure the legacy value of the survey. These categories include the first galaxies at $z\gtrsim10$, faint galaxies during the Epoch of Reionization ($z\sim6-8$), high redshift AGN ($z\gtrsim6$), Population III star candidates, distant quiescent and dusty galaxies ($1\lesssim z \lesssim 6$), and filler galaxies sampling redshift--color--magnitude space from $z\sim 0.1-13$. Seven NIRSpec MSA masks across the extended Abell 2744 cluster were observed, along with NIRCam parallel imaging in 8 filters (F090W, F115W, F150W, F200W, F277W, F356W, F410M, F444W, F480M) over a total area of ~26 arcmin$^2$, overlapping existing HST coverage from programs including the Hubble Frontier Fields and BUFFALO. We successfully observed 553 objects down to $m_{\mathrm{F444W}}\sim30\mathrm{AB}$, and by leveraging mask overlaps, we reach total on-target exposure times ranging from 2.4-16.7h. We demonstrate the success rate and distribution of confirmed redshifts, and also highlight the rich information revealed by these ultradeep spectra for a subset of our targets. An updated lens model of Abell 2744 is also presented, including 14 additional spectroscopic redshifts and finding a total cluster mass of $M_{\mathrm{SL}}=(2.1\pm0.3)\times10^{15}\,\mathrm{M}_{\odot}$. We publicly release reduced 1D and 2D spectra for all objects observed in Summer 2023 along with a spectroscopic redshift catalog and the updated lens model of the cluster (https://jwst-uncover.github.io/DR4.html)., Comment: 19 pages, 9 figures, 4 tables, submitted to ApJ, comments welcome! Data available at: https://jwst-uncover.github.io/DR4.html (v2: figure format correction)

The James Webb Space Telescope (JWST) has uncovered a ubiquitous population of dust-obscured compact sources at $z\gtrsim 4$. Many of these objects exhibit signs of active galactic nucleus (AGN) activity, making their study crucial for understanding the formation of supermassive black holes (SMBHs) and their growth with host galaxies. In this work, we examine low and medium resolution JWST/NIRSpec spectra from the JADES GTO public data release in the GOODS-N field of a red, luminous ($M_{\rm B}\sim-22.2$ mag) and compact ($<500$ pc) source at $z=4.13$. The rest-optical ($\lambda_{\rm rest} > 4000$ A) continuum of this source is strongly dominated by a massive (log$_{10}$[$M_*/M_\odot] \sim 10.6$), quenched (log$_{10}$[sSFR/yr$^{-1}$] $< -11$) galaxy, as indicated by the clear presence of a Balmer break and stellar absorption lines. Star-formation history modeling reveals a starburst episode followed by rapid quenching about 200 Myr ago. The spectrum shows extremely broad (FWHM $\sim 2500$ km/s) H$\alpha$ emission and elevated optical line ratios, indicating an actively accreting SMBH. Moreover, our work has potentially revealed clear AGN signatures in the rest-UV in LRDs for the first time, via a detection of a strong Ly$\alpha$ emission and a broad MgII, doublet. The derived black hole mass of log$_{10}$($M_{\rm BH}/M_\odot) \sim 7.3$ results in $M_{\rm BH}/M_*\sim 0.04$ %, consistent with the local relations, unlike the elevated ratios in other high-$z$ reddened AGN. Finally, we use JWST data from AGN at $z=4-10$ to explore an evolutionary link between high-$z$ reddened AGN, early quiescent galaxies, and local ellipticals., Comment: 20 pages, 7 figures, 2 tables. Submitted to ApJ

The mass-metallicity relation (MZR) provides crucial insights into the baryon cycle in galaxies and provides strong constraints on galaxy formation models. We use JWST NIRSpec observations from the UNCOVER program to measure the gas-phase metallicity in a sample of eight galaxies during the epoch of reionization at $z=6-8$. Thanks to strong lensing of the galaxy cluster Abell 2744, we are able to probe extremely low stellar masses between $10^{6}$ and $10^{8} M_{\odot}$. Using strong lines diagnostics and the most recent JWST calibrations, we derive extremely-low oxygen abundances ranging from 12+log(O/H)=6.7 to 7.8. By combining this sample with more massive galaxies at similar redshifts, we derive a best-fit relation of 12+{\rm log(O/H)}=$0.39_{-0.02}^{+0.02} \times$ log(\mstar) $+ 4.52_{-0.17}^{+0.17}$, which is steeper than determinations at $z \sim 3$. Our results show a clear redshift evolution in the overall normalization of the relation, galaxies at higher redshift having significantly lower metallicities at a given mass. A comparison with theoretical models provides important constraints on which physical processes, such as metal mixing, star formation or feedback recipes, are important in reproducing the observations. Additionally, these galaxies exhibit star formation rates that are higher by a factor of a few to tens compared to extrapolated relations at similar redshifts or theoretical predictions of main-sequence galaxies, pointing to a recent burst of star formation. All these observations are indicative of highly stochastic star formation and ISM enrichment, expected in these low-mass systems, suggesting that feedback mechanisms in high-$z$ dwarf galaxies might be different from those in place at higher masses., Comment: Submitted to ApJL

With stunning clarity, JWST has revealed the Universe's first billion years. The scientific community is analyzing a wealth of JWST imaging and spectroscopic data from that era, and is in the process of rewriting the astronomy textbooks. Here, 1.5 years into the JWST science mission, we provide a snapshot of the great progress made towards understanding the initial chapters of our cosmic history. We highlight discoveries and breakthroughs, topics and issues that are not yet understood, and questions that will be addressed in the coming years, as JWST continues its revolutionary observations of the Early Universe. While this compendium is written by a small number of authors, invited to ISSI Bern in March 2024 as part of the 2024 ISSI Breakthrough Workshop, we acknowledge the work of a large community that is advancing our collective understanding of the evolution of the Early Universe., Comment: review article written by the attendees of the 2024 ISSI breakthrough workshop "The first billion year of the Universe", submitted. Comments welcome

The identification of red, apparently massive galaxies at $z>7$ in early JWST photometry suggests a strongly accelerated timeline compared to standard models of galaxy growth. A major uncertainty in the interpretation is whether the red colors are caused by evolved stellar populations, dust, or other effects such as emission lines or AGN. Here we show that three of the massive galaxy candidates at $z=6.7-8.4$ have prominent Balmer breaks in JWST/NIRSpec spectroscopy from the RUBIES program. The Balmer breaks demonstrate unambiguously that stellar emission dominates at $\lambda_{\rm rest} = 0.4\,\mu$m, and require formation histories extending hundreds of Myr into the past in galaxies only 600--800 Myr after the Big Bang. Two of the three galaxies also show broad Balmer lines, with H$\beta$ FWHM $>2500~{\rm km\,s^{-1}}$, suggesting that dust-reddened AGN contribute to, or even dominate, the SEDs of these galaxies at $\lambda_{\rm rest}\gtrsim 0.6\,\mu$m. All three galaxies have relatively narrow [O III] lines, seemingly ruling out a high-mass interpretation if the lines arise in dynamically-relaxed, inclined disks. Yet, the inferred masses also remain highly uncertain. We model the high-quality spectra using Prospector to decompose the continuum into stellar and AGN components, and explore limiting cases in stellar/AGN contribution. This produces a wide range of possible stellar masses, spanning $M_\star \sim 10^9 - 10^{11}\,{\rm M_{\odot}}$. Nevertheless, all fits suggest a very early and rapid formation, most of which follow with a truncation in star formation. Potential origins and evolutionary tracks for these objects are discussed, from the cores of massive galaxies to low-mass galaxies with over-massive black holes. Intriguingly, we find all of these explanations to be incomplete; deeper and redder data are needed to understand the physics of these systems., Comment: Accepted for publication in ApJL; 20 pages, 10 figures, 1 table

In this paper, we describe the "Medium Bands, Mega Science" JWST Cycle 2 survey (JWST-GO-4111) and demonstrate the power of these data to reveal both the spatially-integrated and spatially-resolved properties of galaxies from the local universe to the era of cosmic dawn. Executed in November 2023, MegaScience obtained ~30 arcmin^2 of deep multiband NIRCam imaging centered on the z~0.3 Abell 2744 cluster, including eleven medium-band filters and the two shortest-wavelength broad-band filters, F070W and F090W. Together, MegaScience and the UNCOVER Cycle 1 treasury program provide a complete set of deep (~28-30 mag) images in all NIRCam medium- and broad-band filters. This unique dataset allows us to precisely constrain photometric redshifts, map stellar populations and dust attenuation for large samples of distant galaxies, and examine the connection between galaxy structures and formation histories. MegaScience also includes ~17 arcmin^2 of NIRISS parallel imaging in two broad-band and four medium-band filters from 0.9-4.8um, expanding the footprint where robust spectral energy distribution (SED) fitting is possible. We provide example SEDs and multi-band cutouts at a variety of redshifts, and use a catalog of JWST spectroscopic redshifts to show that MegaScience improves both the scatter and catastrophic outlier rate of photometric redshifts by factors of 2-3. Additionally, we demonstrate the spatially-resolved science enabled by MegaScience by presenting maps of the [OIII] line emission and continuum emission in three spectroscopically-confirmed z>6 galaxies. We show that line emission in reionization-era galaxies can be clumpy, extended, and spatially offset from continuum emission, implying that galaxy assembly histories are complex even at these early epochs. We publicly release fully reduced mosaics and photometric catalogs for both the NIRCam primary and NIRISS parallel fields., Comment: 21 pages, 10 figures. Fully reduced imaging, photometric catalogs, and photometric redshift fits publicly available at https://jwst-uncover.github.io/megascience/

Within the established framework of structure formation, galaxies start as systems of low stellar mass and gradually grow into far more massive galaxies. The existence of massive galaxies in the first billion years of the Universe, suggested by recent observations, appears to challenge this model, as such galaxies would require highly efficient conversion of baryons into stars. An even greater challenge in this epoch is the existence of massive galaxies that have already ceased forming stars. However, robust detections of early massive quiescent galaxies have been challenging due to the coarse wavelength sampling of photometric surveys. Here we report the spectroscopic confirmation with the James Webb Space Telescope of the quiescent galaxy RUBIES-EGS-QG-1 at redshift $z=4.90$, 1.2 billion years after the Big Bang. Deep stellar absorption features in the spectrum reveal that the galaxy's stellar mass of $10^{11}\,M_\odot$, corroborated by the mass implied by its gas kinematics, formed in a short $200\,$Myr burst of star formation, after which star formation activity dropped rapidly and persistently. According to current galaxy formation models, systems with such rapid stellar mass growth and early quenching are too rare to plausibly occur in the small area probed spectroscopically with JWST. Instead, the discovery of RUBIES-EGS-QG-1 implies that early massive quiescent galaxies can be quenched earlier or exhaust gas available for star formation more efficiently than currently assumed., Comment: 9 figures

Combining the public JWST/NIRCam imaging programs CEERS, PRIMER and JADES, spanning a total area of $\sim500\,{\rm arcmin}^2$, we obtain a sample of $>$30,000 galaxies at $z_{\rm phot}\sim4-9$ that allows us to perform a complete, rest-optical selected census of the galaxy population at $z>3$. Comparing the stellar mass $M_*$ and the UV-slope $\beta$ distributions between JWST- and HST-selected samples, we generally find very good agreement and no significant biases. Nevertheless, JWST enables us to probe a new population of UV-red galaxies that was missing from previous HST-based Lyman Break Galaxy (LBG) samples. We measure galaxy stellar mass functions (SMFs) at $z\sim4-9$ down to limiting masses of $10^{7.5}-10^{8.5}\,{\rm M_\odot}$, finding steep low mass slopes over the entire redshift range, reaching values of $\alpha\approx-2$ at $z\gtrsim6$. At the high-mass end, UV-red galaxies dominate at least out to $z\sim6$. The implied redshift evolution of the SMF suggests a rapid build-up of massive dust-obscured or quiescent galaxies from $z\sim6$ to $z\sim4$ as well as an enhanced efficiency of star formation towards earlier times ($z\gtrsim6$). Finally, we show that the galaxy mass density grows by a factor $\sim20\times$ from $z\sim9$ to $z\sim4$. Our results emphasize the importance of rest-frame optically-selected samples in inferring accurate distributions of physical properties and studying the mass build-up of galaxies in the first 1.5 Gyr of cosmic history., Comment: 31 pages, 17 figures, published in MNRAS

The JWST discovery of ``little red dots'' (LRDs) is reshaping our picture of the early Universe, yet the physical mechanisms driving their compact size and UV-optical colors remain elusive. Here we report an unusually bright LRD ($z=3.1$) observed as part of the RUBIES program. This LRD exhibits broad emission lines (FWHM $\sim4000$km/s), a blue UV continuum, a clear Balmer break and a red continuum sampled out to rest 4 $\mu$m with MIRI. We develop a new joint galaxy and AGN model within the Prospector Bayesian inference framework and perform spectrophotometric modeling using NIRCam, MIRI, and NIRSpec/Prism observations. Our fiducial model reveals a $M_*\sim 10^9M_\odot$ galaxy alongside a dust-reddened AGN driving the optical emission. Explaining the rest-frame optical color as a reddened AGN requires $A_{\rm v}\gtrsim4$, suggesting that a great majority of the accretion disk energy is re-radiated as dust emission. Yet despite clear AGN signatures, we find a surprising lack of hot torus emission, which implies that either the dust emission in this object must be cold, or the red continuum must instead be driven by a massive, evolved stellar population of the host galaxy -- seemingly inconsistent with the high EW broad lines (H$\alpha$ EW $\sim800$\AA). The widths and luminosities of Pa$\beta$, Pa$\delta$, Pa$\gamma$, and H$\alpha$ imply a modest black hole mass of $M_{\rm BH}\sim10^8M_\odot$. Additionally, we identify a narrow blue-shifted HeI absorption in G395M spectra, signaling an ionized outflow with kinetic energy up to $\sim1$\% the luminosity of the AGN. The low redshift of RUBIES-BLAGN-1 combined with the depth and richness of the JWST imaging and spectroscopic observations provide a unique opportunity to build a physical model for these so-far mysterious LRDs, which may prove to be a crucial phase in the early formation of massive galaxies and their supermassive black holes., Comment: 20 pages, 8 figures, 4 tables

We report the spectroscopic confirmation of a massive ($\log(M_\star/M_\odot)=10.34 \pm_{0.07}^{0.06}$), HST-dark ($m_\mathrm{F150W} - m_\mathrm{F444W} = 3.6$) quiescent galaxy at $z_{spec}=3.97$ in the UNCOVER survey. NIRSpec/PRISM spectroscopy and a non-detection in deep ALMA imaging surprisingly reveals that the galaxy is consistent with a low ($<$10 $M_\odot \ \mathrm{yr^{-1}}$) star formation rate despite evidence for moderate dust attenuation. The F444W image is well modeled with a two component \sersic fit that favors a compact, $r_e\sim200$ pc, $n\sim2.9$ component and a more extended, $r_e\sim1.6$ kpc, $n\sim1.7$ component. The galaxy exhibits strong color gradients: the inner regions are significantly redder than the outskirts. Spectral energy distribution models that reproduce both the red colors and low star formation rate in the center of UNCOVER 18407 require both significant ($A_v\sim1.4$ mag) dust attenuation and a stellar mass-weighted age of 900 Myr, implying 50\% of the stars in the core already formed by $z=7.5$. Using spatially resolved annular mass-to-light measurements enabled by the galaxy's moderate magnification ($\mu=2.12\pm_{0.01}^{0.05}$) to reconstruct a radial mass profile from the best-fitting two-component \sersic model, we infer a total mass-weighted $r_\mathrm{eff} = 0.72 \pm_{0.11}^{0.15}$ kpc and log$(\Sigma_\mathrm{1 kpc} \ [\mathrm{M_\odot/kpc^2}]) = 9.61 \pm_{0.10}^{0.08}$. The early formation of a dense, low star formation rate, and dusty core embedded in a less attenuated stellar envelope suggests an evolutionary link between the earliest-forming massive galaxies and their elliptical descendants. Furthermore, the disparity between the global, integrated dust properties and the spatially resolved gradients highlights the importance of accounting for radially varying stellar populations when characterizing the early growth of galaxy structure., Comment: 17 pages, 9 figures, 2 tables. Resubmitted to ApJ after response to referee and update to include new medium band imaging from the JWST MEGASCIENCE program. Comments welcome!

Machine learning photo-z methods, trained directly on spectroscopic redshifts, provide a viable alternative to traditional template fitting methods but may not generalise well on new data that deviates from that in the training set. In this work, we present a Hybrid Algorithm for WI(Y)de-range photo-z estimation with Artificial neural networks and TEmplate fitting (HAYATE), a novel photo-z method that combines template fitting and data-driven approaches and whose training loss is optimised in terms of both redshift point estimates and probability distributions. We produce artificial training data from low-redshift galaxy SEDs at z<1.3, artificially redshifted up to z=5. We test the model on data from the ZFOURGE surveys, demonstrating that HAYATE can function as a reliable emulator of EAZY for the broad redshift range beyond the region of sufficient spectroscopic completeness. The network achieves precise photo-z estimations with smaller errors ($\sigma_{NMAD}$) than EAZY in the initial low-z region (z<1.3), while being comparable even in the high-z extrapolated regime (1.3

With its sensitivity in the rest-frame optical, the James Webb Space Telescope (JWST) has uncovered active galactic nuclei (AGN), comprising both intrinsically faint and heavily reddened sources, well into the first billion years of the Universe, at $z \sim 4-11$. In this work, we revisit the AGN contribution to reionization given the high number densities associated with these objects. We use the DELPHI semi-analytic model, base-lined against the latest high-redshift datasets from the JWST and the Atacama Large millimetre Array (ALMA) to model early star forming galaxies and AGN. We calculate the escape fractions of ionizing radiation from both star formation and AGN and include the impact of reionization feeback in suppressing the baryonic content of low-mass galaxies in ionized regions. This model is validated against the key observables for star forming galaxy, AGN and reionization. In our {\it fiducial} model, reionization reaches its mid-point at $z \sim 6.9$ and ends by $z \sim 5.9$. Low stellar mass ($M_*\leq 10^9M_\odot$) star forming galaxies are found to be the key drivers of the reionization process, providing about $77\%$ of the total photon budget. Despite their high numbers, high accretion rates and higher escape fractions compared to star forming galaxies at $z \sim 5$, AGN only provide about $23\%$ of the total reionization budget which is dominated by black holes in high stellar mass systems (with $M_* \geq 10^9M_\odot$). This is because AGN number densities become relevant only at $z \leq 7$ - as a result, AGN contribute as much as galaxies as late as $z \sim 6.2$, when reionization is already in its end stages. Finally, we find that even contrasting models of the AGN ionizing photon escape fraction (increasing or decreasing with stellar mass) do not qualitatively change our results., Comment: Submitted to A&A; comments welcome

Observations with the James Webb Space Telescope (JWST) have uncovered numerous faint active galactic nuclei (AGN) at $z\sim5$ and beyond. These objects are key to our understanding of the formation of supermassive black holes (SMBHs), their co-evolution with host galaxies, as well as the role of AGN in cosmic reionization. Using photometric colors and size measurements, we perform a search for compact red objects in an array of blank deep JWST/NIRCam fields totaling $\sim640$ arcmin$^{2}$. Our careful selection yields 260 reddened AGN candidates at $4

We present the construction of a deep multi-wavelength PSF-matched photometric catalog in the UDS field following the final UKIDSS UDS DR11 release. The catalog includes photometry in 24 filters, from the MegaCam-uS (0.38 microns) band to the Spitzer-IRAC (8 microns) band, over ~ 0.9 sq. deg. and with a 5-sigma depth of 25.3 AB in the K-band detection image. The catalog, containing approximately 188,564 (136,235) galaxies at 0.2 < z < 8.0 with stellar mass > 10$^{8}$ solar masses 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 to 4 percent at z < 4 across the full brightness range in K-band and stellar mass range 10$^{8}$-10$^{12}$ solar masses. Stellar population properties (e.g., stellar mass, star-formation rate, dust extinction) are derived from the modeling of the spectral energy distributions (SEDs) using the codes FAST and Dense Basis., Comment: 26 pages, 18 figures, accepted in ApJ. Photometric Catalog, catalogs of stellar population properties derived using Eazy and Dense Basis and other high-level products available for public use at the following webpage - https://www.zaidikumail.com/feniks-uds-catalogs (DOI:10.5281/zenodo.11002298)

We present a measurement of the low-mass quiescent size-mass relation at Cosmic Noon (1

Over the past year, JWST has uncovered galaxies at record-breaking distances up to $z \sim 13$. The JWST UNCOVER (ultra-deep NIRSpec and NIRcam observations before the epoch of reionization) program has obtained ultra-deep multiwavelength NIRCam imaging of the massive galaxy cluster Abell 2744 over $\sim 45$ arcmin$^{2}$ down to $\sim 29.5$ AB mag. Here, we present a robust ultraviolet (UV) luminosity function derived through lensing clusters at $99$ in recent JWST studies. In particular, a double power-law (DPL) describes better the bright-end of the luminosity function compared to the classical Schechter form. The number density of these bright galaxies is 10-100 times larger than theoretical predictions and previous findings based on Hubble Space Telescope (HST) observations. Additionally, we measure a star formation rate density of $\rho_{\rm SFR} = 10^{-2.64}$ M$_{\odot}$~yr$^{-1}$~Mpc$^{-3}$ at these redshifts, which is 4 to 10 times higher than galaxy formation models that assume a constant star formation efficiency. Future wide-area surveys and accurate modeling of lensing-assisted observations will reliably constrain both the bright and the dim end of the UV luminosity function at $z>9$, which will provide key benchmarks for galaxy formation models., Comment: Published in MNRAS

The era of the James Webb Space Telescope ushers stellar population models into uncharted territories, particularly at the high-redshift frontier. In a companion paper, we apply the \texttt{Prospector} Bayesian framework to jointly infer galaxy redshifts and stellar population properties from broad-band photometry as part of the UNCOVER survey. Here we present a comprehensive error budget in spectral energy distribution (SED) modeling. Using a sample selected to have photometric redshifts higher than 9, we quantify the systematic shifts stemming from various model choices in inferred stellar mass, star formation rate (SFR), and age. These choices encompass different timescales for changes in the star formation history (SFH), non-universal stellar initial mass functions (IMF), and the inclusion of variable nebular abundances, gas density and ionizing photon budget. We find that the IMF exerts the strongest influence on the inferred properties: the systematic uncertainties can be as much as 1 dex, 2--5 times larger than the formal reported uncertainties in mass and SFR; and importantly, exceed the scatter seen when using different SED fitting codes. Although the assumptions on the lower end of the IMF induce degeneracy, our findings suggest that a common practice in the literature of assessing uncertainties in SED-fitting processes by comparing multiple codes is substantively underestimating the true systematic uncertainty. Highly stochastic SFHs change the inferred SFH by much larger than the formal uncertainties, and introduce $\sim 0.8$ dex systematics in SFR averaged over short time scale and $\sim 0.3$ dex systematics in average age. Finally, employing a flexible nebular emission model causes $\sim 0.2$ dex systematic increase in mass and SFR, comparable to the formal uncertainty. This paper constitutes an initial step toward a complete uncertainty estimate in SED modeling., Comment: Accepted for publication in ApJ. 22 pages, 10 figures, 2 tables

With the remarkable sensitivity and resolution of JWST in the infrared, measuring rest-optical kinematics of galaxies at $z>5$ has become possible for the first time. This study pilots a new method for measuring galaxy dynamics for highly multiplexed, unbiased samples by combining FRESCO NIRCam grism spectroscopy and JADES medium-band imaging. Here we present one of the first JWST kinematic measurements for a galaxy at $z>5$. We find a significant velocity gradient, which, if interpreted as rotation yields $V_{rot} = 240\pm50$km/s and we hence refer to this galaxy as Twister-z5. With a rest-frame optical effective radius of $r_e=2.25$kpc, the high rotation velocity in this galaxy is not due to a compact size as may be expected in the early universe but rather a high total mass, ${\rm log(M}_{dyn}/{\rm M}_\odot)=11.0\pm0.2$. This is a factor of roughly 4x higher than the stellar mass within the effective radius. We also observe that the radial H$\alpha$ equivalent width profile and the specific star formation rate map from resolved stellar population modeling is centrally depressed by a factor of $\sim1.5$ from the center to $r_e$. Combined with the morphology of the line-emitting gas in comparison to the continuum, this centrally suppressed star formation is consistent with a star-forming disk surrounding a bulge growing inside-out. While large, rapidly rotating disks are common to z~2, the existence of one after only 1Gyr of cosmic time, shown for the first time in ionized gas, adds to the growing evidence that some galaxies matured earlier than expected in the history of the universe., Comment: Fig. 3 shows the main result

With the wavelength coverage, sensitivity, and high spatial resolution of JWST, it is now possible to peer through the dust attenuation to probe the rest-frame near infrared (NIR) and stellar structures of extremely dusty galaxies at cosmic noon (z~1-3). In this paper we leverage the combined ALMA and JWST/HST coverage in Abell 2744 to study the multiwavelength (0.5-4.4um) structures of 11 sub-millimeter (sub-mm) detected galaxies at z~0.9-3.5 that are fainter than bright "classical" sub-mm galaxies (SMGs). While these objects reveal a diversity of structures and sizes, all exhibit decreasing sizes and increasing central concentration towards longer wavelengths. The smaller sizes of these objects at long wavelengths indicate that their stellar mass profiles are more compact than their optical light profiles, likely due to centrally-concentrated dust obscuration. Further, we find that galaxies with higher central concentration values tend to have more extreme size ratios (comparing the rest-frame NIR to rest-frame optical); this suggests that the galaxies with the most compact light distributions also have the most concentrated dust distributions. We also find the galaxies with the most extreme size ratios do not have elevated 1.2mm flux densities compared to the rest of our sample: we argue this means compact dust geometry, rather than e.g. high total dust quantity, drives the most extreme observed rest-frame NIR-to-optical size ratios. Upcoming higher resolution 1.2mm ALMA imaging will facilitate joint spatially-resolved analysis and will directly test the dust distributions within this representative sub-mm population., Comment: Submitted to ApJ. 13 pages, 6 figures

The recent UNCOVER survey with the James Webb Space Telescope (JWST) exploits the nearby cluster Abell 2744 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 $z \sim 15$. We show the redshift evolution of stellar ages, star formation rates, and rest-frame colors across the full range of $0.2 \lesssim z \lesssim 15$. The galaxy properties are inferred using the Prospector Bayesian inference framework using informative Prospector-$\beta$ priors on masses and star formation histories to produce joint redshift and stellar population posteriors, and 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 $\sigma_{\rm NMAD} \sim 0.03$, of a similar quality to the established photometric redshift code EAzY. In line with the open-source scientific objective of the Treasury survey, we publicly release the stellar population catalog with this paper, derived from the photometric catalog adapting aperture sizes based on source profiles. This release 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., Comment: Corrected typos: Eq.1 should've been (1-kappa)^2, and the lens maps are normalized to D_ds/D_s=1. These errors were only in the writing; no data products or results were affected. The SPS catalogs are accessible via the UNCOVER survey webpage: https://jwst-uncover.github.io/DR2.html#SPSCatalogs, with a copy deposited to Zenodo: https://doi.org/10.5281/zenodo.8401181

We present the survey design and initial results of the ALMA Cycle 9 program of DUALZ, which aims to establish a joint ALMA and JWST public legacy field targeting the massive galaxy cluster Abell 2744. DUALZ features a contiguous $4'\times6'$ ALMA 30-GHz-wide mosaic in Band 6, covering areas of $\mu>2$ down to a sensitivity of $\sigma=32.7~\mu$Jy. Through a blind search, we identified 69 dust continuum sources at S/N $\gtrsim5.0$ with median redshift and intrinsic 1.2-mm flux of $z=2.30$ and $S_{\rm 1.2mm}^{\rm int}=0.24$~mJy. Of these, 27 have been spectroscopically confirmed, leveraged by the latest NIRSpec observations, while photometric redshift estimates are constrained by the comprehensive HST, NIRCam, and ALMA data for the remaining sources. With priors, we further identify a [CII]158 $\mu$m line emitter at $z=6.3254\pm0.0004$, confirmed by the latest NIRSpec spectroscopy. The NIRCam counterparts of the 1.2-mm continuum exhibit undisturbed morphologies, denoted either by disk or spheroid, implying the triggers for the faint mm emission are less catastrophic than mergers. We have identified 8 HST-dark galaxies (F150W$>$27mag, F150W$-$F444W$>$2.3) and 2 JWST-dark (F444W$>$30mag) galaxy candidates among the ALMA continuum sources. The former includes face-on disk galaxies, hinting that substantial dust obscuration does not always result from inclination. We also detect a marginal dust emission from an X-ray-detected galaxy at $z_{\rm spec}=10.07$, suggesting an active co-evolution of the central black hole and its host. We assess the infrared luminosity function up to $z\sim10$ and find it consistent with predictions from galaxy formation models. To foster diverse scientific outcomes from the community, we publicly release reduced ALMA mosaic maps, cubes, and the source catalog., Comment: 33 pages, 16 figures, and 5 tables. Submitted to ApJS. The ALMA products are fully available from here: https://jwst-uncover.github.io/DR2.html#DUALZ

JWST is revealing a new population of dust-reddened broad-line active galactic nuclei (AGN) at redshifts $z\gtrsim5$. Here we present deep NIRSpec/Prism spectroscopy from the Cycle 1 Treasury program 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 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$\alpha$ with FWHM$\, >2000$ km/s, for $20\%$ 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 $z_{\rm phot}>5$ 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$_{\odot}$. While their UV-luminosities ($-16>M_{\rm UV}>-20$ 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$_{\odot}$ black holes radiating at $\sim 10-40\%$ of Eddington. The number densities are surprisingly high at $\sim10^{-5}$ Mpc$^{-3}$ mag$^{-1}$, 100 times more common than the faintest UV-selected quasars, while accounting for $\sim1\%$ of the UV-selected galaxies. While their UV-faintness suggest they may not contribute strongly to reionization, their ubiquity poses challenges to models of black hole growth., Comment: 23 pages, 9 figures, 5 tables, submitted to ApJ

We report the detection of a 13$\sigma$ H$\alpha$ emission line from HDF850.1 at $z=5.188\pm0.001$ using the FRESCO NIRCam F444W grism observations. Detection of H$\alpha$ in HDF850.1 is noteworthy, given its high far-IR luminosity, substantial dust obscuration, and the historical challenges in deriving its redshift. HDF850.1 shows a clear detection in the F444W imaging data, distributed between a northern and southern component, mirroring that seen in [CII] from the Plateau de Bure Interferometer. Modeling the SED of each component separately, we find that the northern component has a higher mass, star formation rate (SFR), and dust extinction than the southern component. The observed H$\alpha$ emission appears to arise entirely from the less-obscured southern component and shows a similar $\Delta$v$\sim$+130 km/s velocity offset to that seen for [CII] relative to the source systemic redshift. Leveraging H$\alpha$-derived redshifts from FRESCO observations, we find that HDF850.1 is forming in one of the richest environments identified to date at $z>5$, with 100 $z=5.17-5.20$ galaxies distributed across 10 structures and a $\sim$(15 cMpc)$^3$ volume. Based on the evolution of analogous structures in cosmological simulations, the $z=5.17-5.20$ structures seem likely to collapse into a single $>$10$^{14}$ $M_{\odot}$ cluster by $z\sim0$. Comparing galaxy properties forming within this overdensity with those outside, we find the masses, SFRs, and $UV$ luminosities inside the overdensity to be clearly higher. The prominence of H$\alpha$ line emission from HDF850.1 and other known highly-obscured $z>5$ galaxies illustrates the potential of NIRCam-grism programs to map both the early build-up of IR-luminous galaxies and overdense structures., Comment: Submitted to MNRAS. 20 pages, 10 figures and 8 tables (including appendices)

Recent JWST observations have revealed an unexpected abundance of massive galaxy candidates in the early Universe, extending further in redshift and to lower luminosity than what had previously been found by sub-millimeter surveys. These JWST candidates have been interpreted as challenging the $\Lambda$CDM cosmology, but, so far, they have mostly relied only on rest-frame ultraviolet data and lacked spectroscopic confirmation of their redshifts. Here we report a systematic study of 36 massive dust-obscured galaxies with spectroscopic redshifts between $z_{\rm spec}=5-9$ from the JWST FRESCO survey. We find no tension with the $\Lambda$CDM model in our sample. However, three ultra-massive galaxies (log$M_{\star}/M_{\odot}$ $\gtrsim11.0$) require an exceptional fraction of 50% of baryons converted into stars -- two to three times higher than even the most efficient galaxies at later epochs. The contribution from an active nucleus is unlikely because of their extended emission. Ultra-massive galaxies account for as much as 17% of the total cosmic star formation rate density at $z\sim5-6$., Comment: Nature in press. Updated to the accepted version. 24 pages, 4 main figures, 7 supplementary figures, 3 supplementary tables

Deep observations with JWST have revealed an emerging population of red point-like 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$\beta$ line with FWHM = $3439\pm413$ 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 the black hole mass of log$_{10}(M_{\rm BH}/M_\odot)=8.17\pm0.42$, and a bolometric luminosity of $L_{\rm bol}\sim6.6\times10^{45}$ erg s$^{-1}$. These values imply that our object is accreting at $\sim 40\%$ 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 log$_{10}(M_{\rm *}/M_\odot)<8.7$, which would lead to an unprecedented ratio of black hole to host mass of at least $\sim 30 \%$. This is orders of magnitude higher compared to the local QSOs, but is consistent with recent AGN studies at high redshift with JWST. This finding suggests that a non-negligible 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 the galaxy-black hole co-evolution in the early Universe., Comment: 14 pages, 6 figures, 2 tables. Accepted for a publication in ApJL

We present JWST NIRSpec prism spectroscopy of gravitationally lensed galaxies at $z\gtrsim9$ found behind the massive galaxy cluster Abell 2744 in the UNCOVER Cycle 1 Treasury Program. We confirm the source redshift via emission lines and/or the Ly$\alpha$ break feature for ten galaxies at z=8.50-13.08 down to $M_{\rm UV}=-17.3$. We achieve a high confirmation rate of 100\% for $z>9$ candidates reported in Atek et al. (2023). Using six sources with multiple emission line detections, we find that the offset of the redshift estimates between the lines and the Ly$\alpha$ break alone with prism can be as large as $\pm0.2$, raising caution in designing future follow-up spectroscopy for the break-only sources. With spec-$z$ confirmed sources in UNCOVER and the literature, we derive lower limits on the rest-frame ultraviolet (UV) luminosity function (LF) at $z\simeq9$-12 and find these lower limits to be consistent with recent photometric measurements. We identify at least two unambiguous and several possible active galactic nucleus (AGN) systems based on X-ray emission, broad line (BL) H$\beta$, high ionization line (e.g., NIV]1487, CIV1549) detections, and excess in UVLF. This requires the AGN LFs at $z\simeq$ 9-10 to be comparable or even higher than the X-ray AGN LF estimated at $z\sim6$ and indicates a plausible cause of the high abundance of $z>9$ galaxies claimed in recent photometric studies may be AGNs. One UV-luminous source is confirmed at the same redshift as a dusty BL AGN at $z=8.50$ with a physical separation of 380 kpc in the source plane. These two sources show blueward Ly$\alpha$ line or continuum emission, suggesting that they reside in the same ionized bubble with a radius of $7.69\pm0.18$ pMpc. Our results imply that AGNs have a non-negligible contribution to cosmic reionization., Comment: 27 pages, 11 figures, 4 tables, submitted to ApJ (See also arXiv:2308.11610)

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 $\mu$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 indicates T$_{eff}$ = 1300 K and [M/H] $\sim$ $-$1.0, making this one of the few spectroscopically-confirmed T subdwarfs known. The coldest source, UNCOVER-BD-3, is near the T/Y dwarf boundary with T$_{eff}$ = 550 K, and our analysis indicates the presence of PH$_3$ in the 3--5~$\mu$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., Comment: revised, accepted by ApJ 22 Nov 2023

The identification of sources driving cosmic reionization, a major phase transition from neutral Hydrogen to ionized plasma around 600-800 Myr after the Big Bang (Dayal et al. 2018, Mason et al. 2019, Robertson et al. 2022), has been a matter of intense debate (Robertson et al. 2022). Some models suggest that high ionizing emissivity and escape fractions ($f_{\rm esc}$) from quasars support their role in driving cosmic reionization (Madau & Haardt 2015, Mitra et al. 2018). Others propose that the high $f_{\rm esc}$ values from bright galaxies generates sufficient ionizing radiation to drive this process (Naidu et al. 2020). Finally, a few studies suggest that the number density of faint galaxies, when combined with a stellar-mass-dependent model of ionizing efficiency and $f_{\rm esc}$, can effectively dominate cosmic reionization (Finkelstein et al. 2019, Dayal et al. 2020). However, so far, low-mass galaxies have eluded comprehensive spectroscopic studies owing to their extreme faintness. Here we report an analysis of eight ultra-faint galaxies (in a very small field) during the epoch of reionization with absolute magnitudes between $M_{\rm UV}$ $\sim -17$ to $-15$ mag (down to 0.005 $L^{\star}$. We find that faint galaxies during the Universe's first billion years produce ionizing photons with log($\xi_{\mathrm{ion}}$/ Hz erg$^{-1}$) =$25.80\pm 0.14$, a factor of 4 higher than commonly assumed values (Robertson et al. 2015). If this field is representative of the large scale distribution of faint galaxies, the rate of ionizing photons exceeds that needed for reionization, even for escape fractions of order five per cent., Comment: 29 pages, 7 figures, 2 tables. Published in Nature

Early JWST observations have uncovered a new population of red sources that might represent a previously overlooked phase of supermassive black hole growth (Kocevski et al. 2023; Matthee et al. 2023, Labb\'e et al. 2023). One of the most intriguing examples is an extremely red, point-like object that was found to be triply-imaged by the strong lensing (SL) cluster Abell 2744 (Furtak et al. 2023). Here we present deep JWST/NIRSpec observations of this object, Abell2744-QSO1. The spectroscopy confirms that the three images are of the same object, and that it is a highly reddened ($A_V\simeq3$) broad emission-line Active Galactic Nucleus (AGN) at a redshift of $z_{\mathrm{spec}}=7.0451\pm0.0005$. From the width of H$\beta$ ($\mathrm{FWHM}=2800\pm250\,\frac{\mathrm{km}}{\mathrm{s}}$) we derive a black hole mass of $M_{\mathrm{BH}}=4_{-1}^{+2}\times10^7\,\mathrm{M}_{\odot}$. We infer a very high ratio of black hole to galaxy mass of at least 3%, an order of magnitude more than is seen in local galaxies (Bennert et al. 2011), and possibly as high as 100%. The lack of strong metal lines in the spectrum together with the high bolometric luminosity ($L_{\mathrm{bol}}=(1.1\pm0.3)\times10^{45}\,\frac{\mathrm{erg}}{\mathrm{s}}$) indicate that we are seeing the black hole in a phase of rapid growth, accreting at 30% of the Eddington limit. The rapid growth and high black hole to galaxy mass ratio of A2744-QSO1 suggest that it may represent the missing link between black hole seeds (Volonteri et al. 2021) and the first luminous quasars (Fan et al. 2022)., Comment: Published in Nature. Updated to the accepted version

The formation of galaxies by gradual hierarchical co-assembly of baryons and cold dark matter halos is a fundamental paradigm underpinning modern astrophysics and predicts a strong decline in the number of massive galaxies at early cosmic times. Extremely massive quiescent galaxies (stellar masses $>10^{11}$ M$_\odot$) have now been observed as early as 1-2 billions years after the Big Bang; these are extremely constraining on theoretical models as they form 300-500 Myr earlier and only some models can form massive galaxies this early. Here we report on the spectroscopic observations with the James Webb Space Telescope of a massive quiescent galaxy ZF-UDS-7329 at redshift 3.205 $\pm$ 0.005 that eluded deep ground-based spectrscopy, is significantly redder than typical and whose spectrum reveals features typical of much older stellar populations. Detailed modelling shows the stellar population formed around 1.5 billion years earlier in time (z ~ 11) at an epoch when dark matter halos of sufficient hosting mass have not yet assembled in the standard scenario. This observation may point to the presence of undetected populations of early galaxies and the possibility of significant gaps in our understanding of early stellar populations, galaxy formation and/or the nature of dark matter., Comment: 21 pages, 6 figures, updated to reflect accepted version. v3 with figure caption clarified

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 $z_{\rm spec} = 12.393^{+0.004}_{-0.001}$, and a plausible candidate at $z_{\rm spec} = 13.079^{+0.013}_{-0.001}$. 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 ($\sim 10^8~{\rm M_\odot}$), 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 $z \gtrsim 10$ 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., Comment: ApJL in press; 16 pages, 6 figures, 2 tables

The James Webb Space Telescope is now detecting early black holes (BHs) as they transition from "seeds" to supermassive BHs. Recently Bogdan et al. (2023) 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 $z = 10.073 \pm 0.002$. 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 ($M_*\sim 1.4^{+0.3}_{-0.4} \times 10^8 M_\odot$). Given the predicted BH mass ($M_{\rm BH}\sim10^7-10^8 M_\odot$), the resulting ratio of $M_{\rm BH}/M_*$ remains two to three 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., Comment: 10 pages, 4 figures, ApJL in-press. Updated to accepted version incl. X-ray image

The James Webb Space Telescope (JWST) is revolutionizing our knowledge of $z>5$ galaxies and their actively accreting black holes. Using the JWST Cycle 1 Treasury program Ultradeep NIRSpec and NIRCam ObserVations before the Epoch of Reionization (UNCOVER) in the lensing field Abell 2744, we report the identification of a sample of little red dots at $3 < z_{\rm{phot}} < 7$ that likely contain highly-reddened accreting supermassive black holes. Using a NIRCam-only selection to F444W$<27.7$ mag, we find 26 sources over the $\sim45$ arcmin$^{2}$ field that are blue in F115W$-$F200W$\sim0$ (or $\beta_{\rm UV}\sim-2.0$ for $f_{\lambda} \propto \lambda^\beta$), red in F200W$-$F444W = $1-4$ ($\beta_{\rm opt} \sim +2.0$), and are dominated by a point-source like central component. Of the 20 sources with deep ALMA 1.2-mm coverage, none are detected individually or in a stack. For the majority of the sample, SED fits to the JWST+ALMA observations prefer models with hot dust rather than obscured star-formation to reproduce the red NIRCam colors and ALMA 1.2-mm non-detections. While compact dusty star formation can not be ruled out, the combination of extremely small sizes ($\langle r_e \rangle\approx50$ pc after correction for magnification), red rest-frame optical slopes, and hot dust can by explained by reddened broad-line active galactic nuclei (AGNs). Our targets have faint $M_{\rm 1450} \approx -14\ \, {\rm to} -18$ mag but inferred bolometric luminosities of $L_{\rm bol} = 10^{43}-10^{46}$ erg/s, reflecting their obscured nature. If the candidates are confirmed as AGNs with upcoming UNCOVER spectroscopy, then we have found an abundant population of reddened luminous AGN that are at least ten times more numerous than UV-luminous AGN at the same intrinsic bolometric luminosity., Comment: submitted to ApJ

Characterising the prevalence and properties of faint active galactic nuclei (AGN) in the early Universe is key for understanding the formation of supermassive black holes (SMBHs) and determining their role in cosmic reionization. We perform a spectroscopic search for broad H$\alpha$ emitters at $z\approx4-6$ using deep JWST/NIRCam imaging and wide field slitless spectroscopy from the EIGER and FRESCO surveys. We identify 20 H$\alpha$ lines at $z=4.2-5.5$ that have broad components with line widths from $\sim1200-3700$ km s$^{-1}$, contributing $\sim30-90$ % of the total line flux. We interpret these broad components as being powered by accretion onto SMBHs with implied masses $\sim10^{7-8}$ M$_{\odot}$. In the UV luminosity range M$_{\rm UV}=-21$ to $-18$, we measure number densities of $\approx10^{-5}$ cMpc$^{-3}$. This is an order of magnitude higher than expected from extrapolating quasar UV luminosity functions. Yet, such AGN are found in only $<1$ % of star-forming galaxies at $z\sim5$. The SMBH mass function agrees with large cosmological simulations. In two objects we detect narrow red- and blue-shifted H$\alpha$ absorption indicative, respectively, of dense gas fueling SMBH growth and outflows. We may be witnessing early AGN feedback that will clear dust-free pathways through which more massive blue quasars are seen. We uncover a strong correlation between reddening and the fraction of total galaxy luminosity arising from faint AGN. This implies that early SMBH growth is highly obscured and that faint AGN are only minor contributors to cosmic reionization., Comment: 26 pages, 20 figures. Accepted for publication in ApJ. Various improvements and updated citations. Main additions: colours (Fig 11), broad Halpha LF (Fig 18, Sect 5.2), comparisons to simulations (Sect 5.3)

The first JWST data revealed an unexpected population of red galaxies that appear to have redshifts of $z\sim 7-9$ and high masses of $M_*$ $\sim$ 10$^{10}$ M$_{\odot}$ (Labb\'e et al. 2023). Here we fit S\'ersic profiles to the F200W NIRCam images of the 13 massive galaxy candidates of Labb\'e et al., to determine their structural parameters. Satisfactory fits were obtained for nine galaxies. We find that their effective radii are extremely small, ranging from $r_{\rm e}\sim 80$ pc to $r_{\rm e} \sim 300$ pc, with a mean of $\langle r_{\rm e}\rangle \approx 150$ pc. For their apparent stellar masses, the galaxies are smaller than any other galaxy population that has been observed at any other redshift. We use the fits to derive circularized three-dimensional stellar mass profiles of the galaxies, and compare these to the mass profiles of massive quiescent galaxies at $z\sim$2.3 and nearby elliptical galaxies. We find that, despite the high redshift galaxies having $10-20$ times smaller half-light radii, the central stellar densities are comparable to those of their putative descendants at later times. The most straightforward interpretation is that the dense compact inner regions of the most massive ellipticals today were already in place $\sim 600$ Myr after the Big Bang. We caution that the redshifts and masses of the galaxies remain to be confirmed, and that the complex NIRCam point spread function is not yet fully characterized., Comment: Accepted for publication in ApJ Letters

We present new Spitzer Infrared Array Camera (IRAC) 3.6 and 4.5{\mu}m mosaics of three fields, E-COSMOS, DEEP2-F3, and ELAIS-N1. Our mosaics include both new IRAC observations as well as re-processed 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 {\sim} 17 deg2 with a mean integration time of {\sim}1200s, providing a median 5{\sigma} depth of 23.7(23.3) at 3.6(4.5){\mu}m in AB. We perform SExtractor photometry both on the combined mosaics as well as the single-epoch mosaics taken {\sim}6 months apart. The resultant IRAC number counts show good agreement with previous studies. In combination with the wealth of existing and upcoming spectro-photometric 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. counts show good agreement with previous studies., Comment: accepted for publication in AJ

We present the results of a search for high-redshift ($z>9$) galaxy candidates in the JWST UNCOVER survey, using deep NIRCam and NIRISS imaging in 7 bands over $\sim45$ arcmin$^2$ and ancillary HST observations. The NIRCam observations reach a $5-\sigma$ limiting magnitude of $\sim 29.2$ AB. The identification of high$-z$ candidates relies on a combination of a dropout selection and photometric redshifts. We find 16 candidates at $99$. A few galaxies at $z\sim9-10$ appear to show a clear Balmer break between the F356W and F444W/F410M bands, which helps constrain their stellar mass. We estimate blue UV continuum slopes between $\beta=-1.8$ and $-2.3$, typical for early galaxies at $z>9$ but not as extreme as the bluest recently discovered sources. We also find evidence for a rapid redshift-evolution of the mass-luminosity relation and a redshift-evolution of the UV continuum slope for a given range of intrinsic magnitude, in line with theoretical predictions. These findings suggest that deeper JWST observations are needed to reach the fainter galaxy population at those early epochs, and follow-up spectroscopy will help better constrain the physical properties and star formation histories of a larger sample of galaxies., Comment: Submitted to MNRAS

We present the H{\alpha} luminosity function (LF) derived from a large sample of Lyman break galaxies at z {\sim} 4.5 over the GOODS-South and North fields. This study makes use of the new, full-depth Spitzer/IRAC [3.6] and [4.5] imaging from the GOODS Re-ionization Era wide-Area Treasury from the Spitzer program. The H{\alpha} flux is derived from the offset between the continuum flux estimated from the best-fit spectral energy distribution, and the observed photometry in IRAC [3.6]. From these measurements, we build the H{\alpha} LF and study its evolution providing the best constraints of this property at high redshift, where spectroscopy of H{\alpha} is not yet available. Schechter parameterizations of the H{\alpha} LF show a decreasing evolution of {\Phi^\star} with redshift, increasing evolution in L{^\star}, and no significant evolution in the faint-end slope at high z. We find that star formation rates (SFRs) derived from H{\alpha} are higher than those derived from the rest-frame UV for low SFR galaxies but the opposite happens for the highest SFRs. This can be explained by lower mass galaxies (also lower SFR) having, on average, rising star formation histories (SFHs), while at the highest masses the SFHs may be declining. The SFR function is steeper, and because of the excess SFR(H{\alpha}) compared to SFR(UV) at low SFRs, the SFR density estimated from H{\alpha} is higher than the previous estimates based on UV luminosities., Comment: Astrophysical Journal, Accepted, 17 pages, 16 figures

The advent of the James Webb Space Telescope (JWST) signals a new era in exploring galaxies in the high-$z$ universe. Current and upcoming JWST imaging will potentially detect galaxies out to $z \sim 20$, creating a new urgency in the quest to infer accurate photometric redshifts (photo-$z$) for individual galaxies from their spectral energy distributions, as well as masses, ages and star formation rates. Here we illustrate the utility of informed priors encoding previous observations of galaxies across cosmic time in achieving these goals. We construct three joint priors encoding empirical constraints of redshifts, masses, and star formation histories in the galaxy population within the \prospector\ Bayesian inference framework. In contrast with uniform priors, our model breaks an age-mass-redshift degeneracy, and thus reduces the mean bias error in masses from 0.3 to 0.1 dex, and in ages from 0.6 to 0.2 dex in tests done on mock JWST observations. Notably, our model recovers redshifts at least as accurately as the state-of-the-art photo-$z$ code \eazy\ in deep JWST fields, but with two advantages: tailoring a model based on a particular survey renders mostly unnecessary given well-motivated priors; obtaining joint posteriors describing stellar, active galactic nuclei, gas, and dust contributions becomes possible. We can now confidently use the joint distribution to propagate full non-Gaussian redshift uncertainties into inferred properties of the galaxy population. This model, ``\prospector-$\beta$'', is intended for fitting galaxy photometry where the redshift is unknown, and will be instrumental in ensuring the maximum science return from forthcoming photometric surveys with JWST. The code is made publicly available online as a part of \prospector., Comment: Accepted for publication in ApJL. 13 pages, 6 figures, 2 tables. The code is made publicly available online as a part of Prospector; the version used in this work corresponds to the state of the Git repository at commit 820ad72