Search

We present a measurement of the mass–metallicity relation (MZR) at Cosmic Noon, using the JWST near-infrared wide-field slitless spectroscopy obtained by the GLASS-JWST Early Release Science program. By combining the power of JWST and the lensing magnification by the foreground cluster A2744, we extend the measurements of the MZR to the dwarf mass regime at high redshifts. A sample of 50 galaxies with several emission lines is identified across two wide redshift ranges of z = 1.8–2.3 and 2.6–3.4 in the stellar mass range of $\mathrm{log}\,({M}_{* }/{M}_{\odot })\in [6.9,10.0]$ . The observed slope of MZR is 0.223 ± 0.017 and 0.294 ± 0.010 at these two redshift ranges, respectively, consistent with the slopes measured in field galaxies with higher masses. In addition, we assess the impact of the morphological broadening on emission line measurement by comparing two methods of using 2D forward modeling and line profile fitting to 1D extracted spectra. We show that ignoring the morphological broadening effect when deriving line fluxes from grism spectra results in a systematic reduction of flux by ∼30% on average. This discrepancy appears to affect all the lines and thus does not lead to significant changes in flux ratio and metallicity measurements. This assessment of the morphological broadening effect using JWST data presents, for the first time, an important guideline for future work deriving galaxy line fluxes from wide-field slitless spectroscopy, such as Euclid, Roman, and the Chinese Space Station Telescope.

We present the Next Generation Deep Extragalactic Exploratory Public (NGDEEP) Survey, a deep slitless spectroscopic and imaging Cycle 1 JWST treasury survey designed to constrain feedback mechanisms in low-mass galaxies across cosmic time. NGDEEP targets the Hubble Ultra Deep Field (HUDF) with NIRISS slitless spectroscopy ( ${f}_{\mathrm{lim},\mathrm{line},5\sigma }\approx 1.2\,\times \,$ 10 ^−18 erg s ^−1 cm ^−2 ) to measure metallicities and star formation rates (SFRs) for low-mass galaxies through the peak of the cosmic SFR density (0.5 < z < 4). In parallel, NGDEEP targets the HUDF-Par2 parallel field with NIRCam ( ${m}_{\mathrm{lim},5\sigma }=30.6-30.9$ ) to discover galaxies to z > 12, constraining the slope of the faint end of the rest-ultraviolet luminosity function. NGDEEP overlaps with the deepest HST Advanced Camera for Surveys optical imaging in the sky, F435W in the HUDF ( ${m}_{\mathrm{lim},{\rm{F}}435{\rm{W}}}=29.6$ ) and F814W in HUDF-Par2 ( ${m}_{\mathrm{lim},{\rm{F}}814{\rm{W}}}=30$ ), making this a premier HST+JWST deep field. As a treasury survey, NGDEEP data are public immediately, and we will rapidly release data products and catalogs in the spirit of previous deep-field initiatives. In this paper we present the NGDEEP survey design, summarize the science goals, and detail plans for the public release of NGDEEP reduced data products.

GHZ2/GLASS-z12, one of the most distant galaxies found in JWST observations, has been recently observed with both the NIRSpec and MIRI spectrographs, establishing a spectroscopic redshift z _spec = 12.34 and making it the first system at z > 10 with complete spectroscopic coverage from rest-frame UV to optical wavelengths. This galaxy is identified as a strong C iv _λ _1549 emitter (EW = 46 Å) with many other detected emission lines, such as N iv ] _λ _1488 , He ii _λ _1640 , O iii ] _λ _λ _1661,1666 , N iii ] _λ _1750 , C iii ] _λ _λ _1907,1909 , [O ii ] _λ _λ _3726,3729 , [Ne iii ] _λ _3869 , [O iii ] _λ _λ _4959,5007 , and H α , including a remarkable detection of the O iii Bowen fluorescence line at rest frame λ = 3133 Å. We analyze in this paper the joint NIRSpec + MIRI spectral data set. Combining six optical strong-line diagnostics (namely R2, R3, R23, O32, Ne3O2, and Ne3O2Hd), we find extreme-ionization conditions, with log _10 ([O III ] _λ _λ _4959,5007 /[O II ] _λ _λ _3726,3729 ) = 1.39 ± 0.19 and log _10 ([Ne III ] _λ _3869 /[O II ] _λ _λ _3726,3729 ) = 0.37 ± 0.18 in stark excess compared to typical values in the interstellar medium (ISM) at lower redshifts. These line properties are compatible either with an active galactic nucleus (AGN) or with a compact, very dense star-forming environment (Σ _SFR ≃ 10 ^2 –10 ^3 M _⊙ yr ^−1 kpc ^−2 and ${{\rm{\Sigma }}}_{{M}_{{* }}}$ ≃ 10 ^4 –10 ^5 M _⊙ pc ^−2 ), with a high ionization parameter (log _10 ( U ) =−1.75 ± 0.16), a high ionizing photon production efficiency $\mathrm{log}({\xi }_{\mathrm{ion}})={25.7}_{-0.1}^{+0.3}$ , and a low gas-phase metallicity (also confirmed by the direct, T _e method) ranging between 4% and 11% Z _⊙ , indicating a rapid chemical enrichment of the ISM in the past few megayears. These properties also suggest that a substantial amount of ionizing photons (∼10%) are leaking outside of GHZ2 and starting to reionize the surrounding intergalactic medium, possibly due to strong radiation-driven winds. The general lessons learned from GHZ2 are the following: (i) the UV-to-optical combined nebular indicators are broadly in agreement with UV-only or optical-only indicators; (ii) UV+optical diagnostics fail to discriminate between an AGN and star formation in a low-metallicity, high-density, and extreme-ionization environment; and (iii) comparing the nebular line ratios with local analogs may be approaching its limits at z ≳ 10, as this approach is potentially challenged by the unique conditions of star formation experienced by galaxies at these extreme redshifts.

We spectroscopically confirm the M _UV = −20.5 mag galaxy GHZ2/GLASS-z12 to be at redshift z = 12.34. The source was selected via NIRCam photometry in GLASS-JWST Early Release Science data, providing the first evidence of a surprising abundance of bright galaxies at z ≳ 10. The NIRSpec PRISM spectrum shows detections of N iv , C iv , He ii , O iii , C iii , O ii , and Ne iii lines and the first detection at high redshift of the O iii Bowen fluorescence line at 3133 Å rest frame. The prominent C iv line with rest-frame equivalent width (EW) ≈ 46 Å puts GHZ2 in the category of extreme C iv emitters. GHZ2 displays UV lines with EWs that are only found in active galactic nuclei (AGNs) or composite objects at low/intermediate redshifts. The UV line-intensity ratios are compatible with both AGNs and star formation in a low-metallicity environment, with the low limit on the [Ne iv ]/[N iv ] ratio favoring a stellar origin of the ionizing photons. We discuss a possible scenario in which the high ionizing output is due to low-metallicity stars forming in a dense environment. We estimate a metallicity ≲0.1 Z / Z _⊙ , a high ionization parameter log U > −2, a N/O abundance 4–5 times the solar value, and a subsolar C/O ratio similar to the recently discovered class of nitrogen-enhanced objects. Considering its abundance patterns and the high stellar mass density (10 ^4 M _⊙ pc ^−2 ), GHZ2 is an ideal formation site for the progenitors of today's globular clusters. The remarkable brightness of GHZ2 makes it a “Rosetta stone” for understanding the physics of galaxy formation within just 360 Myr after the Big Bang.

The Next Generation Deep Extragalactic Exploratory Public (NGDEEP) survey program was designed specifically to include Near Infrared Slitless Spectroscopic observations (NGDEEP-NISS) to detect multiple emission lines in as many galaxies as possible and across a wide redshift range using the Near Infrared Imager and Slitless Spectrograph. We present early results obtained from the first set of observations (Epoch 1, 50% of the allocated orbits) of this program (NGDEEP-NISS1). Using a set of independently developed calibration files designed to deal with a complex combination of overlapping spectra, multiple position angles, and multiple cross filters and grisms, in conjunction with a robust and proven algorithm for quantifying contamination from overlapping dispersed spectra, NGDEEP-NISS1 has achieved a 3 σ sensitivity limit of 2 × 10 ^−18 erg s ^−1 cm ^−2 . We demonstrate the power of deep wide field slitless spectroscopy (WFSS) to characterize the star formation rates, and metallicity ([O iii ]/H β ), and dust content, of galaxies at 1 < z < 3.5. The latter showing intriguing initial results on the applicability and assumptions made regarding the use of Case B recombination. Further, we identify the presence of active galactic nuclei and infer the mass of their supermassive black holes using broadened restframe Mg ii and H β emission lines. The spectroscopic results are then compared with the physical properties of galaxies extrapolated from fitting spectral energy distribution models to photometry alone. The results clearly demonstrate the unique power and efficiency of WFSS at near-infrared wavelengths over other methods to determine the properties of galaxies across a broad range of redshifts.

We present a robust sample of very high redshift galaxy candidates from the first epoch of JWST/NIRCam imaging from the Next Generation Deep Extragalactic Exploratory Public (NGDEEP) survey. The NGDEEP NIRCam imaging, spanning 9.7 arcmin ^2 in the Hubble Ultra Deep Field Parallel Field 2, reaches m = 30.4 (5 σ , point-source, 2″ diameter apertures corrected to total) in F277W, making it the deepest public JWST GO imaging data set to date. We describe our detailed data reduction process of the six-filter broadband JWST/NIRCam imaging, incorporating custom corrections for systematic effects to produce high-quality calibrated images. Using robust photometric redshift selection criteria, we identify a sample of 38 z ≳ 9 galaxy candidates. These objects span a redshift range of z = 8.5–15.8 and apparent magnitudes of m _F277W = 27–30.5 AB mag, reaching ∼1.5 mag deeper than previous public JWST imaging surveys. We calculate the rest-frame ultraviolet luminosity function at z ∼ 9 and 11 and present a new measurement of the luminosity function faint-end slope at z ∼ 11. We find a faint-end slope of α = −2.5 ± 0.4 and −2.2 ± 0.2 at z ∼ 9 and 11, respectively. This is consistent with no significant evolution in the faint-end slope and number density from z = 9 to 11. Comparing our results with theoretical predictions, we find that some models produce better agreement at the faint end than the bright end. These results will help to constrain how stellar feedback impacts star formation at these early epochs.

We combine JWST/NIRCam imaging and MUSE data to characterize the properties of galaxies in different environmental conditions in the cluster Abell2744 ( z = 0.3064) and in its immediate surroundings. We investigate how galaxy colors, morphology, and star-forming fractions depend on wavelength and on different parameterizations of environment. Our most striking result is the discovery of a “red excess” population in F200W−F444W colors in both the cluster regions and the field. These galaxies have normal F115W−F150W colors but are up to 0.8 mag redder than red sequence galaxies in F200W−F444W. They also have rather blue rest-frame B − V colors. Galaxies in the field and at the cluster virial radius are overall characterized by redder colors, but galaxies with the largest color deviations are found in the field and in the cluster core. Several results suggest that mechanisms taking place in these regions might be more effective in producing these colors. Looking at their morphology, many cluster galaxies show signatures consistent with ram pressure stripping, while field galaxies have features resembling interactions and mergers. Our hypothesis is that these galaxies are characterized by dust-enshrouded star formation: a JWST/NIRSpec spectrum for one of the galaxies is dominated by a strong PAH at 3.3 μ m, suggestive of dust-obscured star formation. Larger spectroscopic samples are needed to understand whether the color excess is due exclusively to dust-obscured star formation, as well as the role of environment in triggering it.

We report the detection of a high density of redshift z ≈ 10 galaxies behind the foreground cluster A2744, selected from imaging data obtained recently with NIRCam on board JWST by three programs—GLASS-JWST, UNCOVER, and DDT#2756. To ensure robust estimates of the lensing magnification μ , we use an improved version of our model that exploits the first epoch of NIRCam images and newly obtained MUSE spectra and avoids regions with μ > 5 where the uncertainty may be higher. We detect seven bright z ≈ 10 galaxies with demagnified rest frame −22 ≲ M _UV ≲ −19 mag, over an area of ∼37 arcmin ^2 . Taking into account photometric incompleteness and the effects of lensing on luminosity and cosmological volume, we find that the density of z ≈ 10 galaxies in the field is about 10× (3×) larger than the average at M _UV ≈ −21 ( −20) mag reported so far. The density is even higher when considering only the GLASS-JWST data, which are the deepest and the least affected by magnification and incompleteness. The GLASS-JWST field contains five out of seven galaxies, distributed along an apparent filamentary structure of 2 Mpc in projected length, and includes a close pair of candidates with M _UV < −20 mag having a projected separation of only 16 kpc. These findings suggest the presence of a z ≈ 10 overdensity in the field. In addition to providing excellent targets for efficient spectroscopic follow-up observations, our study confirms the high density of bright galaxies observed in early JWST observations but calls for multiple surveys along independent lines of sight to achieve an unbiased estimate of their average density and a first estimate of their clustering.

We present JWST/NIRSpec prism spectroscopy of seven galaxies selected from Cosmic Evolution Early Release Science (CEERS) survey NIRCam imaging with photometric redshifts z _phot > 8. We measure emission line redshifts of z = 7.65 and 8.64 for two galaxies. For two other sources without securely detected emission lines we measure $z={9.77}_{-0.29}^{+0.37}$ and ${10.01}_{-0.19}^{+0.14}$ by fitting model spectral templates to the prism data, from which we detect continuum breaks consistent with Ly α opacity from a mostly neutral intergalactic medium. The presence of strong breaks and the absence of strong emission lines give high confidence that these two galaxies have redshifts z > 9.6, but the redshift values derived from the breaks alone have large uncertainties given the low spectral resolution and relatively low S/N of the CEERS NIRSpec prism data. The two z ∼ 10 sources observed are relatively luminous ( M _UV < −20), with blue continua (−2.3 ≲ β ≲ −1.9) and low dust attenuation ( ${A}_{V}\simeq {0.15}_{-0.1}^{+0.3}$ ); and at least one of them has a high stellar mass for a galaxy at that redshift ( $\mathrm{log}({M}_{\star }/{M}_{\odot })\simeq {9.3}_{-0.3}^{+0.2}$ ). Considered together with spectroscopic observations of other CEERS NIRCam-selected high- z galaxy candidates in the literature, we find a high rate of redshift confirmation and low rate of confirmed interlopers (8%). Ten out of 35 z > 8 candidates with CEERS NIRSpec spectroscopy do not have secure redshifts, but the absence of emission lines in their spectra is consistent with redshifts z > 9.6. We find that z > 8 photometric redshifts are generally in agreement (within their uncertainties) with the spectroscopic values, but also that the photometric redshifts tend to be slightly overestimated (〈Δ z 〉 = 0.45 ± 0.11), suggesting that current templates do not fully describe the spectra of very-high- z sources. Overall, the spectroscopy solidifies photometric redshift evidence for a high spatial density of bright galaxies at z > 8 compared to theoretical model predictions, and further disfavors an accelerated decline in the integrated UV luminosity density at z > 8.

We present results from the Cosmic Evolution Early Release Survey on the stellar population parameters for 28 galaxies with redshifts 4 < z < 9 using imaging data from the James Webb Space Telescope (JWST) Mid-Infrared Instrument (MIRI) combined with data from the Hubble Space Telescope and the Spitzer Space Telescope. The JWST/MIRI 5.6 and 7.7 μ m data extend the coverage of the rest-frame spectral energy distribution to nearly 1 μ m for galaxies in this redshift range. By modeling the galaxies’ SEDs the MIRI data show that the galaxies have, on average, rest-frame UV (1600 Å)— I -band colors 0.4 mag bluer than derived when using photometry that lacks MIRI. Therefore, the galaxies have lower ratios of stellar mass to light. The MIRI data reduce the stellar masses by $\langle {\rm{\Delta }}\mathrm{log}{M}_{* }\rangle =0.25$ dex at 4 < z < 6 and 0.37 dex at 6 < z < 9. This also reduces the star formation rates (SFRs) by 〈ΔlogSFR〉 = 0.14 dex at 4 < z < 6 and 0.27 dex at 6 < z < 9. The MIRI data also improve constraints on the allowable stellar mass formed in early star formation. We model this using a star formation history that includes both a “burst” at z _f = 100 and a slowly varying (“delayed- τ ”) model. The MIRI data reduce the allowable stellar mass by 0.6 dex at 4 < z < 6 and by ≈1 dex at 6 < z < 9. Applying these results globally, this reduces the cosmic stellar-mass density by an order of magnitude in the early Universe ( z ≈ 9). Therefore, observations of rest-frame ≳1 μ m are paramount for constraining the stellar-mass buildup in galaxies at very high redshifts.

The JWST observations of high-redshift galaxies are used to measure their star formation histories—the buildup of stellar mass in the earliest galaxies. Here we use a novel analysis program, SEDz*, to compare near-IR spectral energy distributions for galaxies with redshifts 5 < z < 7 to combinations of stellar population templates evolved from z = 12. We exploit NIRCam imaging in seven wide bands covering 1–5 μ m taken in the context of the GLASS-JWST-ERS program and use SEDz* to solve for well-constrained star formation histories for 24 exemplary galaxies. In this first look, we find a variety of histories, from long, continuous star formation over 5 < z < 12 to short but intense starbursts, sometimes repeating, and, most commonly, contiguous mass buildup lasting ∼0.5 Myr, possibly the seeds of today’s typical M * galaxies.

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.

Lyman-break galaxy (LBG) candidates at z ≳ 10 are rapidly being identified in James Webb Space Telescope (JWST)/NIRCam observations. Due to the (redshifted) break produced by neutral hydrogen absorption of rest-frame UV photons, these sources are expected to drop out in the bluer filters while being well detected in redder filters. However, here we show that dust-enshrouded star-forming galaxies at lower redshifts ( z ≲ 7) may also mimic the near-infrared (near-IR) colors of z > 10 LBGs, representing potential contaminants in LBG candidate samples. First, we analyze CEERS-DSFG-1, a NIRCam dropout undetected in the F115W and F150W filters but detected at longer wavelengths. Combining the JWST data with (sub)millimeter constraints, including deep NOEMA interferometric observations, we show that this source is a dusty star-forming galaxy (DSFG) at z ≈ 5.1. We also present a tentative 2.6 σ SCUBA-2 detection at 850 μ m around a recently identified z ≈ 16 LBG candidate in the same field and show that, if the emission is real and associated with this candidate, the available photometry is consistent with a z ∼ 5 dusty galaxy with strong nebular emission lines despite its blue near-IR colors. Further observations on this candidate are imperative to mitigate the low confidence of this tentative submillimeter emission and its positional uncertainty. Our analysis shows that robust (sub)millimeter detections of NIRCam dropout galaxies likely imply z ∼ 4–6 redshift solutions, where the observed near-IR break would be the result of a strong rest-frame optical Balmer break combined with high dust attenuation and strong nebular line emission, rather than the rest-frame UV Lyman break. This provides evidence that DSFGs may contaminate searches for ultra-high redshift LBG candidates from JWST observations.

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.

We present an investigation into the first 500 Myr of galaxy evolution from the Cosmic Evolution Early Release Science (CEERS) survey. CEERS, one of 13 JWST ERS programs, targets galaxy formation from z ∼ 0.5 to >10 using several imaging and spectroscopic modes. We make use of the first epoch of CEERS NIRCam imaging, spanning 35.5 arcmin ^2 , to search for candidate galaxies at z > 9. Following a detailed data reduction process implementing several custom steps to produce high-quality reduced images, we perform multiband photometry across seven NIRCam broad- and medium-band (and six Hubble broadband) filters focusing on robust colors and accurate total fluxes. We measure photometric redshifts and devise a robust set of selection criteria to identify a sample of 26 galaxy candidates at z ∼ 9–16. These objects are compact with a median half-light radius of ∼0.5 kpc. We present an early estimate of the z ∼ 11 rest-frame ultraviolet (UV) luminosity function, finding that the number density of galaxies at M _UV ∼ −20 appears to evolve very little from z ∼ 9 to 11. We also find that the abundance (surface density [arcmin ^−2 ]) of our candidates exceeds nearly all theoretical predictions. We explore potential implications, including that at z > 10, star formation may be dominated by top-heavy initial mass functions, which would result in an increased ratio of UV light per unit halo mass, though a complete lack of dust attenuation and/or changing star formation physics may also play a role. While spectroscopic confirmation of these sources is urgently required, our results suggest that the deeper views to come with JWST should yield prolific samples of ultrahigh-redshift galaxies with which to further explore these conclusions.

We present the serendipitous discovery of a late T-type brown dwarf candidate in JWST NIRCam observations of the Early Release Science Abell 2744 parallel field. The discovery was enabled by the sensitivity of JWST at 4 μ m wavelengths and the panchromatic 0.9–4.5 μ m coverage of the spectral energy distribution. The unresolved point source has magnitudes F115W = 27.95 ± 0.15 and F444W = 25.84 ± 0.01 (AB), and its F115W−F444W and F356W−F444W colors match those expected for other known T dwarfs. We can exclude it as a reddened background star, high redshift quasar, or a very high redshift galaxy. Comparison with stellar atmospheric models indicates a temperature of T _eff ≈ 650 K and surface gravity $\mathrm{log}g\approx 5.25$ , implying a mass of 0.03 M _⊙ and age of 5 Gyr. We estimate the distance of this candidate to be 570–720 pc in a direction perpendicular to the Galactic plane, making it a likely thick disk or halo brown dwarf. These observations underscore the power of JWST to probe the very low-mass end of the substellar mass function in the Galactic thick disk and halo.

We report the discovery of a candidate galaxy with a photo- z of z ∼ 12 in the first epoch of the James Webb Space Telescope (JWST) Cosmic Evolution Early Release Science Survey. Following conservative selection criteria, we identify a source with a robust z _phot = ${11.8}_{-0.2}^{+0.3}$ (1 σ uncertainty) with m _F200W = 27.3 and ≳7 σ detections in five filters. The source is not detected at λ < 1.4 μ m in deep imaging from both Hubble Space Telescope (HST) and JWST and has faint ∼3 σ detections in JWST F150W and HST F160W, which signal a Ly α break near the red edge of both filters, implying z ∼ 12. This object (Maisie’s Galaxy) exhibits F115W − F200W > 1.9 mag (2 σ lower limit) with a blue continuum slope, resulting in 99.6% of the photo- z probability distribution function favoring z > 11. All data-quality images show no artifacts at the candidate’s position, and independent analyses consistently find a strong preference for z > 11. Its colors are inconsistent with Galactic stars, and it is resolved ( r _h = 340 ± 14 pc). Maisie’s Galaxy has log M _* / M _⊙ ∼ 8.5 and is highly star-forming (log sSFR ∼ −8.2 yr ^−1 ), with a blue rest-UV color ( β ∼ −2.5) indicating little dust, though not extremely low metallicity. While the presence of this source is in tension with most predictions, it agrees with empirical extrapolations assuming UV luminosity functions that smoothly decline with increasing redshift. Should follow-up spectroscopy validate this redshift, our universe was already aglow with galaxies less than 400 Myr after the Big Bang.

Ly α emission from galaxies can be used to trace neutral hydrogen in the epoch of reionization, however, there is a degeneracy between the attenuation of Ly α in the intergalactic medium (IGM) and the line profile emitted by the galaxy. Large shifts of Ly α redward of systemic due to scattering in the interstellar medium can boost Ly α transmission in the IGM during reionization. The relationship between the Ly α velocity offset from systemic and other galaxy properties is not well established at high redshift or low luminosities, due to the difficulty of observing emission lines which trace the systemic redshift. Rest-frame optical spectroscopy with JWST/NIRSpec has opened a new window into understanding Ly α at z > 3. We present a sample of 12 UV-faint galaxies (−20 ≲ M _UV ≲ −16) at 3 ≲ z ≲ 6, with Ly α velocity offsets, Δ v _Ly _α , measured from the Very Large Telescope/MUSE and JWST/NIRSpec from the GLASS-JWST Early Release Program. We find a median Δ v _Ly _α of 205 km s ^−1 and standard deviation of 75 km s ^−1 , compared to 320 and 170 km s ^−1 , respectively, for M _UV < −20 galaxies in the literature. Our new sample demonstrates the previously observed trend of decreasing Ly α velocity offset with decreasing UV luminosity and optical line velocity dispersion, which extends to M _UV ≳ −20, consistent with a picture where the Ly α profile is shaped by gas close to the systemic redshift. Our results imply that during reionization Ly α from UV-faint galaxies will be preferentially attenuated, but that detecting Ly α with low Δ v _Ly _α can be an indicator of large ionized bubbles.

We present a new high-precision, JWST-based, strong-lensing model for the galaxy cluster Abell 2744 at z = 0.3072. By combining the deep, high-resolution JWST imaging from the Grism Lens Amplified Survey from Space–JWST and Ultradeep NIRSpec and NIRCam Observations before the Epoch of Reionization programs and a Director’s Discretionary Time program, with newly obtained Very Large Telescope/Multi Unit Spectroscopic Explorer (MUSE) data, we identify 32 multiple images from 11 background sources lensed by two external subclusters at distances of ∼160″ from the main cluster. The new MUSE observations enable the first spectroscopic confirmation of a multiple-image system in the external clumps. Moreover, the reanalysis of the spectrophotometric archival and JWST data yields 27 additional multiple images in the main cluster. The new lens model is constrained by 149 multiple images (∼66% more than in our previous model) covering an extended redshift range between 1.03 and 9.76. The subhalo mass component of the cluster includes 177 member galaxies down to m _F160W = 21, of which 163 are spectroscopically confirmed. Internal velocity dispersions are measured for 85 members. The new lens model is characterized by a remarkably low scatter between the predicted and observed positions of the multiple images (0.″43). This precision is unprecedented given the large multiple-image sample, the complexity of the cluster mass distribution, and the large modeled area. The improved precision and resolution of the cluster total mass distribution provides a robust magnification map over a ∼30 arcmin ^2 area, which is critical for inferring the intrinsic physical properties of the highly magnified, high- z sources. The lens model and the new MUSE redshift catalog are released with this publication.

We present images and a multiwavelength photometric catalog based on all of the JWST NIRCam observations obtained to date in the region of the Abell 2744 galaxy cluster. These data come from three different programs, namely, the GLASS-JWST Early Release Science Program, UNCOVER, and the Director’s Discretionary Time program 2756. The observed area in the NIRCam wide-band filters—covering the central and extended regions of the cluster, as well as new parallel fields—is 46.5 arcmin ^2 in total. All images in eight bands (F090W, F115W, F150W, F200W, F277W, F356W, F410M, and F444W) have been reduced adopting the latest calibration and reference files available. Data reduction has been performed using an augmented version of the official JWST pipeline, with improvements aimed at removing or mitigating defects in the raw images and improving the background subtraction and photometric accuracy. We obtain an F444W-detected multiband catalog, including all NIRCam and available Hubble Space Telescope data, adopting forced-aperture photometry on point-spread-function-matched images. The catalog is intended to enable early scientific investigations and is optimized for the study of faint galaxies; it contains 24,389 sources, with a 5 σ limiting magnitude in the F444W band ranging from 28.5 AB to 30.5 AB, as a result of the varying exposure times of the surveys that observed the field. We publicly release the reduced NIRCam images, associated multiwavelength catalog, and the code adopted for 1/ f noise removal with the aim of aiding users in familiarizing themselves with JWST NIRCam data and identifying suitable targets for follow-up observations.

We report the observation by the Atacama Large Millimeter/submillimeter Array (ALMA) of a z ≳ 10 galaxy candidate (GHZ1) discovered from the GLASS–JWST Early Release Science Program. Our ALMA program aims to detect the [O iii ] emission line at the rest-frame frequency 3393.0062 GHz (88.36 μ m) and far-IR continuum emission with the spectral window setup seamlessly covering a 26.125 GHz frequency range (10.10 < z < 11.14). A total of 7 hr of on-source integration was employed, using four frequency settings to cover the full range (1.7 hr per setting), with 0.″7 angular resolution. No line or continuum is clearly detected, with 5 σ upper limits on the line emission of 0.93 mJy beam ^−1 at 25 km s ^−1 channel ^−1 and on the continuum emission of 30 μ Jy beam ^−1 . We report marginal spectral (at 225 km s ^−1 resolution) and continuum features (4.1 σ and 2.6 σ peak signal-to-noise ratio, respectively), within 0.″17 from the JWST position of GHZ1. This spectral feature implies z = 10.38 and needs to be verified with further observations. Assuming that the best estimate of photometric redshift ( $z={10.60}_{-0.60}^{+0.52}$ ) is correct, the model of the galaxy’s broadband spectral energy distribution for the 3 σ upper limit of the continuum flux from GHZ1 suggests that GHZ1 has a small amount of dust ( M _d ≲ 10 ^4 M _⊙ ) at a high temperature ( T _d ≳ 90 K). The 5 σ upper limit on the [O iii ] _88 _μ _m line luminosity and the inferred star formation rate of GHZ1 are consistent with the properties of low-metallicity dwarf galaxies. We also report serendipitous clear detections of six continuum sources at the locations of the JWST galaxy counterparts in the field.

In this paper we investigate how the Reionization process is affected by early galaxy formation in different cosmological scenarios. We use a semi-analytic model with suppressed initial power spectra to obtain the UV Luminosity Function in thermal Warm Dark Matter and sterile neutrino cosmologies. We retrace the ionization history of intergalactic medium with hot stellar emission only, exploiting fixed and variable photons escape fraction models (fesc). For each cosmology, we find an upper limit to fixed fesc, which guarantees the completion of the process at z<6.7. The analysis is tested with two limit hypothesis on high-z ionized hydrogen volume fraction, comparing our predictions with observational results.