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We present an analysis of JWST Lyαspectroscopy ofz≳ 6.5 galaxies, using observations in the public archive covering galaxies in four independent fields: Great Observatories Origins Deep Survey (GOODS)-N, GOODS-S, A2744, and the Extended Groth Strip (EGS). We measure the Lyαemission line properties for a sample of 210z≃ 6.5–13 galaxies, with redshifts confirmed independently of Lyαin all cases. We present three new detections of Lyαemission in JWST spectra, including a large equivalent width (EW; =143 Å) Lyαemitter (LAE) with strong Civemission (EW = 21 Å) atz= 7.1 in GOODS-N. We measure the redshift-dependent LyαEW distribution across our sample. We find that strong Lyαemission (EW > 25 Å) becomes increasingly rare at earlier epochs, suggesting that the transmission of Lyαphotons decreases by 4× betweenz≃ 5 andz≃ 9. We describe potential implications for the intergalactic medium neutral fraction. There is significant field-to-field variance in the LAE fraction. In contrast to the three other fields, the EGS shows no evidence for reduced transmission of Lyαphotons atz≃ 7–8, suggesting a significantly ionized sight line may be present in the field. We use available NIRCam grism observations from the First Reionization Epoch Spectroscopically Complete Observations survey to characterize overdensities on large scales around known LAEs in the GOODS fields. The strongest overdensities appear linked with extremely strong Lyαdetections (EW > 50 Å) in most cases. Future Lyαspectroscopy with JWST has the potential to constrain the size of ionized regions around early galaxy overdensities, providing a new probe of the reionization process.

We investigate the multiphase structure of gas flows in galaxies. We study 80 galaxies during the epoch of peak star formation (1.4 ≤z≤ 2.7) using data from the Keck/Low-Resolution Imaging Spectrometer (LRIS) and the Very Large Telescope/K-Band Multi-Object Spectrograph (KMOS). Our analysis provides a simultaneous probe of outflows using UV emission and absorption features and Hαemission. With this unprecedented data set, we examine the properties of gas flows estimated from LRIS and KMOS in relation to other galaxy properties, such as star formation rate (SFR), SFR surface density (Σ_SFR), stellar mass (M_*), and main-sequence offset (ΔMS). We find no strong correlations between outflow velocity measured from rest-UV line centroids and galaxy properties. However, we find that galaxies with detected outflows show higher averages in SFR, Σ_SFR, and ΔMS than those lacking outflow detections, indicating a connection between outflow and galaxy properties. Furthermore, we find a lower average outflow velocity than previously reported, suggesting greater absorption at the systemic redshift of the galaxy. Finally, we detect outflows in 49% of our LRIS sample and 30% in the KMOS sample and find no significant correlation between outflow detection and inclination. These results may indicate that outflows are not collimated and that Hαoutflows have a lower covering fraction than low-ionization interstellar absorption lines. Additionally, these tracers may be sensitive to different physical scales of outflow activity. A larger sample size with a wider dynamic range in galaxy properties is needed to further test this picture.

JWST observations have recently begun delivering the first samples of Lyαvelocity profile measurements atz> 6, opening a new window into the reionization process. Interpretation ofz≳ 6 line profiles is currently stunted by limitations in our knowledge of the intrinsic Lyαprofile (before encountering the intergalactic medium (IGM)) of the galaxies that are common atz≳ 6. To overcome this shortcoming, we have obtained resolved (R∼ 3900) Lyαspectroscopy of 42 galaxies atz= 2.1–3.4 with similar properties as are seen atz> 6. We quantify a variety of Lyαprofile statistics as a function of [Oiii]+Hβequivalent width (EW). Our spectra reveal a new population ofz≃ 2–3 galaxies with large [Oiii]+HβEWs (>1200 Å) and a large fraction of Lyαflux emerging near the systemic redshift (peak velocity ≃0 km s⁻¹). These spectra indicate that low-density neutral hydrogen channels are able to form in a subset of low-mass galaxies (≲1 × 10⁸M_⊙) that experience a burst of star formation (sSFR > 100 Gyr⁻¹). Other extreme [Oiii] emitters show weaker Lyαthat is shifted to higher velocities (≃240 km s⁻¹) with little emission near the line center. We investigate the impact the IGM is likely to have on these intrinsic line profiles in the reionization era, finding that the centrally peaked Lyαemitters should be strongly attenuated atz≳ 5. We show that these line profiles are particularly sensitive to the impact of resonant scattering from infalling IGM and can be strongly attenuated even when the IGM is highly ionized atz≃ 5. We compare these expectations against a new database ofz≳ 6.5 galaxies with robust velocity profiles measured with JWST/NIRSpec.

Spitzer/Infrared Array Camera (IRAC) imaging has revealed that the brightest z ∼ 7−8 galaxies often exhibit young ages and strong nebular line emission, hinting at high ionizing efficiency among early galaxies. However, IRAC’s limited sensitivity has long hindered efforts to study the fainter, more numerous population often thought largely responsible for reionization. Here, we use Cosmic Evolution Early Release Science (CEERS) JWST/NIRCam data to characterize 116 ultraviolet (UV)-faint (median MUV = −19.5) z ∼ 6.5−8 galaxies. The spectral energy distributions are typically dominated by young (∼10–50 Myr), low-mass (M* ∼ 108 M⊙) stellar populations, and we find no need for extremely high stellar masses (∼1011 M⊙). Considering previous studies of UV-bright (MUV ∼ −22) z ∼ 7−8 galaxies, we find evidence for a strong (5–10 times) increase in specific star formation rate (sSFR) toward lower luminosities (median sSFR = 103 Gyr−1 in CEERS). The larger sSFRs imply a more dominant contribution from OB stars in the relatively numerous UV-faint population, perhaps suggesting that these galaxies are very efficient ionizing agents (median ξion = 1025.7 erg−1 Hz). In spite of the much larger sSFRs, we find little increase in [O iii] + H  β equivalent widths towards fainter MUV (median ≈780 $\mathrm{\mathring{A}}$). If confirmed, this may indicate that a substantial fraction of our CEERS galaxies possess extremely low metallicities (≲3 per cent Z⊙) where [O iii] emission is suppressed. Alternatively, high ionizing photon escape fractions or bursty star formation histories can also weaken the nebular lines in a subset of our sample. While the majority of galaxies in our sample are very blue (median β = −2.0), we identify a significant tail of very dusty galaxies (β ∼ −1) at ≈0.5$L_\mathrm{UV}^\ast$ which may contribute significantly to the z ∼ 7−8 star formation rate density.

We report on the discovery of cool gas inflows towards three star-forming galaxies at <z> ∼ 2.30. Analysis of Keck Low-Resolution Imaging Spectrometer spectroscopy reveals redshifted low-ionization interstellar (LIS) metal absorption lines with centroid velocities of 60–130 km s−1. These inflows represent some of the most robust detections of inflowing gas into isolated, star-forming galaxies at high redshift. Our analysis suggests that the inflows are due to recycling metal-enriched gas from previous ejections. Comparisons between the galaxies with inflows and a larger parent sample of 131 objects indicate that galaxies with detected inflows may have higher specific star formation rates (sSFRs) and star-formation-rate surface densities (ΣSFR). However, when additional galaxies without robustly detected inflows based on centroid velocity but whose LIS absorption line profiles indicate large red-wing velocities are considered, galaxies with inflows do not show unique properties relative to those lacking inflows. Additionally, we calculate the covering fraction of cool inflowing gas as a function of red-wing inflow velocity, finding an enhancement in high-sSFR binned galaxies, likely due to an increase in the amount of recycling gas. Together, these results suggest that the low detection rate of galaxies with cool inflows is primarily related to the viewing angle rather than the physical properties of the galaxies.

Reionization is thought to be driven by faint star-forming galaxies, but characterizing this population has long remained very challenging. Here, we utilize deep nine-band JADES (JWST Advanced Deep Extragalactic Survey)/NIRCam (Near-Infrared Camera) imaging to study the star-forming and ionizing properties of 756 $z\sim 6-9$ galaxies, including hundreds of very ultraviolet (UV)-faint objects ($M_\mathrm{UV}\gt -18$). The faintest ($m\sim 30$) galaxies in our sample typically have stellar masses of $M_\ast \sim (1-3)\times 10^7\ \mathrm{ M}_\odot$ and young light-weighted ages ($\sim$50 Myr), though some show strong Balmer breaks implying much older ages ($\sim$500 Myr). We find no evidence for extremely massive galaxies ($\gt 3\times 10^{10}\ \mathrm{ M}_\odot$) in our sample. We infer a strong (factor $\gt $2) decline in the typical [O iii]$+$H $\beta$ equivalent widths (EWs) towards very faint $z\sim 6-9$ galaxies, yet a weak UV luminosity dependence on the H $\alpha$ EWs at $z\sim 6$. We demonstrate that these EW trends can be explained if fainter galaxies have systematically lower metallicities as well as more recently declining star formation histories relative to the most UV-luminous galaxies. Our data provide evidence that the brightest galaxies are frequently experiencing a recent strong upturn in star formation rate. We also discuss how the EW trends may be influenced by a strong correlation between $M_\mathrm{UV}$ and Lyman continuum escape fraction. This alternative explanation has dramatically different implications for the contribution of galaxies along the luminosity function to cosmic reionization. Finally, we quantify the photometric overdensities around two $z\,\gt\,7$ strong Ly $\alpha$ emitters. One Ly $\alpha$ emitter lies close to a strong photometric overdensity, while the other shows no significant nearby overdensity, perhaps implying that not all strong $z\,\gt\, 7$ Ly $\alpha$ emitters reside in large ionized bubbles.

We present a catalog of 717 candidate galaxies atz> 8 selected from 125 square arcmin of NIRCam imaging as part of the JWST Advanced Deep Extragalactic Survey (JADES). We combine the full JADES imaging data set with data from the JWST Extragalactic Medium Survey and First Reionization Epoch Spectroscopic COmplete Survey (FRESCO) along with extremely deep existing observations from Hubble Space Telescope (HST)/Advanced Camera for Surveys (ACS) for a final filter set that includes 15 JWST/NIRCam filters and five HST/ACS filters. The high-redshift galaxy candidates were selected from their estimated photometric redshifts calculated using a template-fitting approach, followed by visual inspection from seven independent reviewers. We explore these candidates in detail, highlighting interesting resolved or extended sources, sources with very red long-wavelength slopes, and our highest-redshift candidates, which extend toz_phot∼ 18. Over 93% of the sources are newly identified from our deep JADES imaging, including 31 new galaxy candidates atz_phot> 12. We also investigate potential contamination by stellar objects, and do not find strong evidence from spectral energy distribution fitting that these faint high-redshift galaxy candidates are low-mass stars. Using 42 sources in our sample with measured spectroscopic redshifts from NIRSpec and FRESCO, we find excellent agreement to our photometric redshift estimates, with no catastrophic outliers and an average difference of 〈Δz=z_phot−z_spec〉 = 0.26. These sources comprise one of the most robust samples for probing the early buildup of galaxies within the first few hundred million years of the Universe’s history.