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We present deep JWST NIRSpec observations in the sight line of MACS J1149.5+2223, a massive cluster of galaxies at z = 0.54. We report the spectroscopic redshift of 28 sources at 3 < z < 9.1, including nine sources with the detection of the OIIIλ4363 auroral line. Combining these with 16 OIIIλ4363 -detected sources from publicly available JWST data, our sample consists of 25 galaxies with robust gas-phase metallicity measurements via the direct method. We observe a positive correlation between stellar mass and metallicity, with an ∼0.5 dex offset down below the local relation. Interestingly, we find a larger-than-expected scatter of ∼0.3 dex around the relation, which cannot be explained by redshift evolution among our sample or other third parameters. The scatter increases at higher redshift, and we tentatively attribute this to the enrichment process having higher stochasticity, due to shallower potential wells, more intense feedback processes, and a higher galaxy merger rate. Despite reaching a considerably low-mass regime ( logM*/M⊙∼7.3 ), our samples have metallicity of log(O/H) +12 ≳ 7, i.e., comparable to the most metal-poor galaxies in the local Universe. The search for primordial galaxies may be accomplished by extending toward a lower mass and/or by investigating inhomogeneities at smaller spatial scales. Lastly, we investigate potential systematics caused by the limitation of JWST’s Micro-Shutter Assembly observations. Caution is warranted when the target exceeds the slit size, as this situation could allow an overestimation of global metallicity, especially under the presence of a strong negative metallicity gradient.

We present measurements of the gas-phase oxygen and nitrogen abundances obtained by applying the direct method to JWST NIRspec R ∼ 1000 spectroscopy for six galaxies at redshift greater than 3. Our measurements are based on rest-frame optical nitrogen [N ii]λλ6548,6583 lines and are complemented by six additional objects from the literature at 3 ≤ z ≤ 6. We find that 9 out of 12 objects have values of log(N/O) that are compatible with those found for low-redshift, metal-poor, dwarf galaxies and for H ii regions of more luminous local galaxies. However, 3 out of 12 objects have log(N/O) values that are overabundant compared to what is expected on the basis of their oxygen abundance. We explore a few standard scenarios to explain the observations and conclude that, within the limited statistics available to us, none of them can be definitely excluded even though we prefer dilution by pristine gas infall in between star formation bursts, as this is predicted by simulations to take place as a natural part of bursty star formation.

Lyα emission is possibly the best indirect diagnostic of Lyman continuum (LyC) escape since the conditions that favor the escape of Lyα photons are often the same that allow for the escape of LyC photons. In this work, we present the rest-frame UV–optical spectral characteristics of 11 Lyα emitting galaxies at 3 < z < 6—the redshift range that optimizes between intergalactic medium attenuation effects and temporal proximity to the epoch of reionization. From a combined analysis of JWST/NIRSpec and MUSE data, we present the Lyα escape fraction and study its correlation with other physical properties of galaxies that might facilitate Lyα escape. We find that our galaxies have low masses (80% of the sample with log10M⋆<9.5M⊙ ), compact sizes (median R e ∼ 0.7 kpc), low dust content, moderate [O iii]/[O ii] flux ratios (mean ∼ 6.8 ± 1.2), and moderate Lyα escape fractions (mean fescLyα∼ 0.11). Our sample shows characteristics that are broadly consistent with low-redshift galaxies with Lyα emission, which are termed as “analogs” of the high-redshift population. We predict the LyC escape fraction in our sample to be low (0.03–0.07), although larger samples in the postreionization epoch are needed to confirm these trends.

Lyα emission from galaxies can be used to trace neutral hydrogen in the epoch of reionization, however, there is a degeneracy between the attenuation of Lyα in the intergalactic medium (IGM) and the line profile emitted by the galaxy. Large shifts of Lyα redward of systemic due to scattering in the interstellar medium can boost Lyα transmission in the IGM during reionization. The relationship between the Lyα 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 Lyα at z > 3. We present a sample of 12 UV-faint galaxies (−20 ≲ M UV ≲ −16) at 3 ≲ z ≲ 6, with Lyα velocity offsets, Δv Lyα , measured from the Very Large Telescope/MUSE and JWST/NIRSpec from the GLASS-JWST Early Release Program. We find a median Δv Lyα 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 Lyα velocity offset with decreasing UV luminosity and optical line velocity dispersion, which extends to M UV ≳ −20, consistent with a picture where the Lyα profile is shaped by gas close to the systemic redshift. Our results imply that during reionization Lyα from UV-faint galaxies will be preferentially attenuated, but that detecting Lyα with low Δv Lyα can be an indicator of large ionized bubbles.

In the first billion years after the Big Bang, sources of ultraviolet (UV) photons are believed to have ionized intergalactic hydrogen, rendering the Universe transparent to UV radiation. Galaxies brighter than the characteristic luminosity L * (refs.  1 , 2 ) do not provide enough ionizing photons to drive this cosmic reionization. Fainter galaxies are thought to dominate the photon budget; however, they are surrounded by neutral gas that prevents the escape of the Lyman-α photons, which has been the dominant way to identify them so far. JD1 was previously identified as a triply-imaged galaxy with a magnification factor of 13 provided by the foreground cluster Abell 2744 (ref. 3 ), and a photometric redshift of z  ≈ 10. Here we report the spectroscopic confirmation of this very low luminosity (≈0.05  L *) galaxy at z  = 9.79, observed 480 Myr after the Big Bang, by means of the identification of the Lyman break and redward continuum, as well as multiple ≳4 σ emission lines, with the Near-InfraRed Spectrograph (NIRSpec) and Near-InfraRed Camera (NIRCam) instruments. The combination of the James Webb Space Telescope (JWST) and gravitational lensing shows that this ultra-faint galaxy ( M UV  = −17.35)—with a luminosity typical of the sources responsible for cosmic reionization—has a compact (≈150 pc) and complex morphology, low stellar mass (10 7.19   M ⊙ ) and subsolar (≈0.6  Z ⊙ ) gas-phase metallicity. The JWST, with the aid of gravitational lensing, confirms the extreme distance of an ultra-faint galaxy at a redshift of 9.79, showing it to have a luminosity typical of the sources responsible for cosmic reionization and highly compact and complex morphology.

During the second half of Cycle 1 of the James Webb Space Telescope (JWST), we conducted the Parallel Application of Slitless Spectroscopy to Analyze Galaxy Evolution (PASSAGE) program. PASSAGE received the largest allocation of JWST observing time in Cycle 1, 591 hr of NIRISS observations to obtain direct near-IR imaging and slitless spectroscopy. About two-thirds of this was ultimately executed, to observe 63 high-latitude fields in pure-parallel mode. These have provided more than 10,000 near-infrared grism spectrograms of faint galaxies. PASSAGE brings unique advantages in studying galaxy evolution: (a) Unbiased spectroscopic search, without prior photometric preselection. By including the typical galaxies which have low masses and strong emission lines, slitless spectroscopy is the indispensable complement to any pretargeted spectroscopy. (b) The combination of several dozen independent fields to overcome cosmic variance. (c) Near-infrared spectral coverage, spanning a wide wavelength range of up to 1.0 to 2.3 μm, with minimal wavelength gaps, to measure multiple diagnostic rest-frame optical lines, minimizing sensitivity to dust reddening. (d) JWST’s unprecedented spatial resolution, in some cases using two orthogonal grism orientations, to overcome contamination due to blending of overlapping spectra. (e) Discovery of rare bright objects especially for detailed JWST follow-up. PASSAGE data are public immediately, and our team plans to deliver fully processed high-level data products. In this PASSAGE overview, we describe the survey and data quality, and present examples of these accomplishments in several areas of current interest in the evolution of emission-line galaxy properties, particularly at low masses.

Ly\\(\\) emission is possibly the best indirect diagnostic of Lyman continuum (LyC) escape since the conditions that favor the escape of Ly\\(\\) photons are often the same that allows for the escape of LyC photons. In this work, we present the rest UV-optical spectral characteristics of 11 Ly\\(\\) emitting galaxies at 3 \\(<\\) z \\(<\\) 6 - the optimal redshift range chosen to avoid the extreme IGM attenuation while simultaneously studying galaxies close enough to the epoch of reionization. From a combined analysis of JWST/NIRSpec and MUSE data, we present the Ly\\(\\) escape fraction and study their correlations with other physical properties of galaxies that might facilitate Ly\\(\\) escape. We find that our galaxies have low masses (80\\% of the sample with \\( log_10 \\ M_ < 9.5\\ M_\\)), compact sizes (median \\( R_e 0.7 \\ kpc \\)), low dust content, moderate [OIII]/[OII] flux ratios (mean \\(\\) 6.8 \\(\\) 1.2), and moderate Ly\\(\\) escape fraction (mean \\( f_esc^Ly \\ \\) 0.11). Our sample show characteristics that are broadly consistent with the low redshift galaxies with Ly\\(\\) emission, which are termed as \"analogs\" of high redshift population. We predict the Lyman continuum escape fraction in our sample to be low (0.03-0.07), although larger samples in the post-reionization epoch are needed to confirm these trends.

Lyman-alpha (Ly\\(\\)) 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\\(\\) in the intergalactic medium (IGM) and the line profile emitted from the galaxy. Large shifts of Ly\\(\\) redward of systemic due to scattering in the interstellar medium can boost Ly\\(\\) transmission in the IGM during reionization. The relationship between Ly\\(\\) 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 systemic redshift. Rest-frame optical spectroscopy with JWST/NIRSpec has opened a new window into understanding of Ly\\(\\) at z>3. We present a sample of 12 UV-faint galaxies (\\(-20 \\) MUV \\( -16\\)) at \\(3 z 6\\), with Ly\\(\\) velocity offsets, \\( v_Ly\\), measured from VLT/MUSE and JWST/NIRSpec from the GLASS-JWST Early Release Program. We find median \\( v_Ly\\) of 205 km s\\(^-1\\) and standard deviation 75 km s\\(^-1\\), compared to 320 and 170km s\\(^-1\\) for MUV < -20 galaxies in the literature. Our new sample demonstrates the previously observed trend of decreasing Ly\\(\\) velocity offset with decreasing UV luminosity and optical line velocity dispersion, extends to MUV \\(\\) -20, consistent with a picture where the Ly\\(\\) profile is shaped by gas close to the systemic redshift. Our results imply that during reionization Ly\\(\\) from UV-faint galaxies will be preferentially attenuated, but that detecting Ly\\(\\) with low \\( v_Ly\\) can be an indicator of large ionized bubbles.

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 both in 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\\( m\\), suggestive of dust obscured star formation. Larger spectroscopic samples are needed to understand if the color excess is due exclusively to dust-obscured star formation, and the role of environment in triggering it.

We present measurements of the gas-phase Oxygen and Nitrogen abundances obtained by applying the direct method to JWST NIRspec \\(R1000\\) spectroscopy for 6 galaxies at redshift greater than 3. Our measurements are based on rest-frame optical Nitrogen [N II]\\(_6548,6583\\) lines and are complemented by 6 additional objects from the literature at \\(3 z 6\\). We find that 9 out of 12 objects have values of log(N/O) that are compatible with those found for low-redshift, metal-poor, dwarf galaxies and for HII regions of more luminous local galaxies. However, 3 out of 12 objects have log(N/O) values that are overabundant compared to what is expected on the basis of their Oxygen abundance. We explore a few standard scenarios to explain the observations and conclude that, within the limited statistics available to us, none of them can be definitely excluded even though we prefer dilution by pristine gas infall in between star formation bursts as this is predicted by simulations to take place as a natural part of bursty star formation.