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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 (104 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.

We present the first spatially resolved measurements of galaxy properties in the JWST ERO SMACS 0723 field. We perform a comprehensive analysis of five 5 < z < 9 galaxies with spectroscopic redshifts from NIRSpec observations. We perform spatially resolved spectral energy distribution fitting with Bagpipes, using six NIRCam imaging bands spanning the wavelength range 0.8–5 μm. This approach allows us to study the internal structure and assembly of the first generations of galaxies. We find clear gradients both in the empirical color maps and in most of the estimated physical parameters. We find regions of considerably different specific star formation rates across each galaxy, which points to very bursty star formation happening on small scales, not galaxy-wide. The integrated light is dominated by these bursty regions, which exhibit strong line emission, with the equivalent width of [O iii]+Hβ reaching up to ∼3000–4000 Å rest frame. Studying these galaxies in an integrated approach yields extremely young inferred ages of the stellar population (<10 Myr), which outshine older stellar populations that are only distinguishable in the spatially resolved maps. This leads to inferring ∼0.5–1 dex lower stellar masses by using single-aperture photometry, when compared to resolved analyses. Such systematics would have strong implications in the shape and evolution of the stellar mass function at these early times, particularly while samples are limited to small numbers of the brightest candidates. Furthermore, the evolved stellar populations revealed in this study imply an extended process of early galaxy formation that could otherwise be hidden behind the light of the most recently formed stars.

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 arcmin2. 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 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 Lyα emission. We place 2σ upper limits on the rest-frame equivalent width <16–28 Å. Based on the tight upper limits to the Lyα emission, we constrain the volume-averaged neutral fraction of hydrogen in the intergalactic medium to be x HI > 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 × 1011 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 × 1015 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 <20 hr total exposure time. Follow-up spectroscopy of the remaining photometric candidates of the overdensity will further refine the features of this system and help characterize the role of such overdensities in cosmic reionization.

JWST spectroscopy has built large emission line samples at z ≳ 4, but it has yet to confidently reveal many galaxies with the hard radiation fields commonly associated with active galactic nucleus photoionization. While this may indicate a weaker UV ionizing spectrum in many z > 4 active galactic nuclei or obscuration from dense neutral gas and dust, the complete picture remains unclear owing to the small number of deep rest-UV spectra. Here, we characterize the strength of high-ionization lines in 53 new galaxies observed with NIRSpec R = 2700 grating spectroscopy. We present new detections of narrow N v λ1240 in two galaxies. One is a previously confirmed z = 6.98 little red dot (LRD) with broad Hβ, and the other is a z = 8.72 galaxy with a narrow-line spectrum. Neither source exhibits C iv or He ii emission, indicating large N v/C iv and N v/He ii ratios that may reflect a combination of nitrogen-enhancement and resonant scattering effects. We investigate the incidence of narrow high-ionization lines in a large database of 851 NIRSpec grating spectra, and we separately quantify the fraction of LRDs with narrow high-ionization UV emission lines. Our results likely suggest that hard radiation fields are indeed present in a small subset of LRDs ( 12.5−10.4+23.7% ) and UV-selected galaxies ( 2.2−1.0+1.7% ) at z > 4. The identification of narrow high-ionization lines in the population of LRDs with strong Balmer absorption suggests that the dense neutral hydrogen gas may not uniformly cover the nucleus. The strong N v (coupled with weak C iv and He ii) suggests that efforts to identify high-ionization lines should extend down in wavelength to the N v doublet.

We characterize the JWST spectra of 61 galaxies at z = 9−14, including 30 newly confirmed galaxies. We directly compare the z > 9 spectroscopic properties against 401 galaxies at 6 < z < 9, with the goal of identifying evolution in the star formation histories and interstellar medium. We measure rest-UV emission-line properties and UV continuum slopes, while also investigating the rest-optical emission lines for the subset of galaxies at 9.0 < z < 9.6. With these spectra, we constrain the stellar masses, specific star formation rates (sSFRs), dust attenuation, and the average metallicity and abundance pattern of z > 9 galaxies. Our dataset indicates that the emission lines undergo a marked change at z > 9, with extremely large C III], Hβ, and Hγ equivalent widths becoming 2 and 3× more common at z > 9 relative to 6 < z < 9. Using the spectra, we infer the distribution of star formation rates (SFRs) on short (SFR3Myr) and medium (SFR3−50Myr) timescales, finding that rapid SFR upturns (large SFR3Myr/SFR3−50Myr ratios) are significantly more likely among z > 9 galaxies. These results may reflect a larger dispersion in UV luminosity at fixed halo mass and larger baryon accretion rates at z > 9, although other physical effects may also contribute. We suggest that the shift in star formation conditions explains the prevalence of extreme nebular spectra that have been detected at z > 9, with hard ionizing sources and nitrogen enhancements becoming more typical at the highest redshifts. Finally, we identify five z > 9 spectroscopically confirmed galaxies with red UV colors (β ≳ −1.5), revealing either a small population with moderate dust attenuation (τV = 0.23−0.35) or very high density nebular-dominated galaxies with hot stellar populations.

We introduce the Bias-free Extragalactic Analysis for Cosmic Origins with NIRCam (BEACON) survey, a JWST Cycle 2 program allocated up to 600 pure-parallel hours of observations. BEACON explores high-latitude areas of the sky with JWST/NIRCam over ∼100 independent sight lines, totaling ∼0.3 deg2, reaching a median F444W depth of ≈28.2 AB mag (5σ). Based on existing JWST observations in legacy fields, we estimate that BEACON will photometrically identify 25–150 galaxies at z > 10 and 500–1000 at z ∼ 7–10 uniquely enabled by an efficient multiple filter configuration spanning 0.9–5.0 μm. The expected sample size of z > 10 galaxies will allow us to obtain robust number density estimates and to discriminate between different models of early star formation. In this paper, we present an overview of the survey design and initial results using the first 19 fields. We present 129 galaxy candidates at z ≳7 identified in those fields, including 11 galaxies at z ≳10 and several UV-luminous (MUV < −21 mag) galaxies at z ∼ 8. The number densities of z < 13 galaxies inferred from the initial fields are overall consistent with those in the literature. Despite reaching a considerably large volume (∼105 Mpc3), however, we find no galaxy candidates at z > 13, providing us with a complimentary insight into early galaxy evolution with minimal cosmic variance. We publish imaging and catalog data products for these initial fields. Upon survey completion, all BEACON data will be coherently processed and distributed to the community along with catalogs for redshift and other physical quantities.

We report the detection of Lyα in CANUCS-LRD-z8.6, a recently discovered active galactic nucleus (AGN) at z = 8.63 by R. Tripodi et al. (2025), in new NIRSpec/MSA G140H/F070LP observations. We detect broad Lyα emission (FWHM = 1540 ± 260 km s−1) near the systemic velocity, which suggests a large ionizing bubble, considering that the Universe is almost fully neutral at the redshift. Through Lyα line-shape modeling assuming a Strömgren sphere, we find a large bubble radius, Rb = 1.5−0.2+0.3 pMpc, and a moderately high Lyα escape fraction, fesc = 11% ± 3%. The intrinsic line width is inferred to be broad (2200 ± 280 km s−1), likely originating in the broad-line region. Existing data indicate that CANUCS-LRD-z8.6 is within a mild overdensity, δ = 1.8−0.6+3.0 , suggesting that other galaxies in its proximity might have contributed to the formation of the bubble. The high N IV]λ1488/C IVλ1548 and N IV]λ1488/O III]λ1661 line ratios measured in existing NIRSpec/PRISM data indicate nitrogen enrichment in this metal-poor, low-luminosity AGN. The spectroscopic features are overall similar to those of other nitrogen-rich galaxies discovered in the literature, such as GN-z11 and GHZ2/GLASSz12. This suggests that CANUCS-LRD-z8.6 may represent one of the evolutionary phases of those nitrogen-rich galaxies.

How galaxies drive reionization and what governs its geometry remain fundamental questions. We present JWST/NIRCam wide-field slitless spectroscopy (WFSS) observations toward two of the most Lyα-transmissive QSO sight lines near the end of reionization. We find that regions at z ∼ 5.7 along both sight lines previously found to be low-density in Lyα emitters are also underdense in [O iii] emitters, with densities less than half the cosmic mean. Other transmissive regions, however, are found to coincide with average-density environments, indicating that multiple pathways may produce high intergalactic medium (IGM) transmission. For the first time, we measure the 2D cross-correlation between IGM transmission and galaxy positions, revealing evidence for anisotropic ionization geometry. Specifically, we detect enhanced transmission at transverse distances of Δr ∼ 0.8 times the mean free path, consistent with ionizing photons escaping preferentially along large-scale structures that are aligned with, but offset from, the line of sight. This anisotropic escape may contribute to the observed patchiness of reionization and challenge the assumption of isotropic ionized bubble growth in current models.

Lyα spectroscopy with JWST is opening a new window on the sizes of ionized bubbles through the reionization epoch. Theoretical expectations suggest typical bubble radii should be 0.6–1.5 pMpc at z ≃ 7, assuming neutral hydrogen fractions of the intergalactic medium in the range x¯HI = 0.5–0.7. Here, we investigate this picture using JWST to characterize the environment and Lyα emission of 292 galaxies at 7.0 < z < 8.5 across five fields spanning a comoving volume of 1.3 × 106 Mpc3. If the reionization predictions are correct, we should see overdensities and strong Lyα emission clustered in redshift windows of dz = 0.04–0.08 and angular scales of 5′–11′. We detect Lyα emission in 36 out of 292 galaxies, including nine new Lyα detections, two of which (in the UltraDeep Survey field) show extremely large equivalent widths (EW = 200−78+50 Å and 284−75+56 Å). We identify 13 significant (4–11×) galaxy overdensities using redshifts from NIRCam grism and NIRSpec. Strong Lyα emitters are almost uniformly found in the overdensities, with nearly all located between the center and back of the structures. The overdensities that host the strong Lyα emitters span typical line-of-sight distances (dz ∼ 0.14) and angular scales (∼8′) that are comparable to the predicted bubble sizes at z ≃ 7. We discuss evidence that the Extended Groth Strip is mostly ionized along a 24 pMpc sight line at z ≃ 7.0–7.6, based on the presence of three overdense structures and 10 Lyα emitters in this volume, and find such a large ionized region would pose tension with standard reionization models.