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The first few 100 Myr at z > 10 mark the last major uncharted epoch in the history of the universe, where only a single galaxy (GN-z11 at z ≈ 11) is currently spectroscopically confirmed. Here we present a search for luminous z > 10 galaxies with JWST/NIRCam photometry spanning ≈1–5 μm and covering 49 arcmin2 from the public JWST Early Release Science programs (CEERS and GLASS). Our most secure candidates are two M UV ≈ −21 systems: GLASS-z12 and GLASS-z10. These galaxies display abrupt ≳1.8 mag breaks in their spectral energy distributions (SEDs), consistent with complete absorption of flux bluewards of Lyα that is redshifted to z = 12.4 − 0.3 + 0.1 and z = 10.4 − 0.5 + 0.4 . Lower redshift interlopers such as quiescent galaxies with strong Balmer breaks would be comfortably detected at >5σ in multiple bands where instead we find no flux. From SED modeling we infer that these galaxies have already built up ∼109 solar masses in stars over the ≲300–400 Myr after the Big Bang. The brightness of these sources enable morphological constraints. Tantalizingly, GLASS-z10 shows a clearly extended exponential light profile, potentially consistent with a disk galaxy of r 50 ≈ 0.7 kpc. These sources, if confirmed, join GN-z11 in defying number density forecasts for luminous galaxies based on Schechter UV luminosity functions, which require a survey area >10× larger than we have studied here to find such luminous sources at such high redshifts. They extend evidence from lower redshifts for little or no evolution in the bright end of the UV luminosity function into the cosmic dawn epoch, with implications for just how early these galaxies began forming. This, in turn, suggests that future deep JWST observations may identify relatively bright galaxies to much earlier epochs than might have been anticipated.

Radial mass-to-light ratio gradients cause the half-mass and half-light radii of galaxies to differ, potentially biasing studies that use half-light radii. Here we present the largest catalog to date of galaxy half-mass radii at z > 1: 7,006 galaxies in the CANDELS fields at 1.0 ≤ z ≤ 2.5. The sample includes both star-forming and quiescent galaxies with stellar masses 9.0 ≤ log (M * /M ) ≤ 11.5. We test three methods for calculating half-mass radii from multi-band PSF-matched HST imaging: two based on spatially-resolved SED modeling, and one that uses a rest-frame color profile. All three methods agree, with scatter 0.3 dex. In agreement with previous studies, most galaxies in our sample have negative color gradients (the centers are redder than the outskirts, and r e,mass < r e,light ). We find that color gradient strength has significant trends with increasing stellar mass, half-light radius, U − V color, and stellar mass surface density. These trends have not been seen before at z > 1. Furthermore, color gradients of star-forming and quiescent galaxies show a similar redshift evolution: they are flat at z 2, then steeply decrease as redshift decreases. This affects the galaxy mass-size relation. The normalizations of the star-forming and quiescent r mass − M * relations are 10-40% smaller than the corresponding r light − M * relations; the slopes are ∼ 0.1 − 0.3 dex shallower. Finally, the half-mass radii of star-forming and quiescent galaxies at M * = 10 10.5 M only grow by ∼ 1% and ∼ 8% between z ∼ 2.25 and z ∼ 1.25. This is significantly less than the ∼ 37% and ∼ 47% size increases found when using the half-light radius.

The physical mechanisms that quench star formation, turning blue star-forming galaxies into red quiescent galaxies, remain unclear. In this Letter, we investigate the role of gas supply in suppressing star formation by studying the molecular gas content of post-starburst galaxies. Leveraging the wide area of the Sloan Digital Sky Survey, we identify a sample of massive intermediate-redshift galaxies that have just ended their primary epoch of star formation. We present Atacama Large Millimeter/submillimeter Array CO(2-1) observations of two of these post-starburst galaxies at z∼0.7 with M M 2 10 11 *~´ . Their molecular gas reservoirs of 6.4 0.8 ( ) M 10 9  and M 34.0 1.6 10 9 ´ ( ) are an order of magnitude larger than comparable-mass galaxies in the local universe. Our observations suggest that quenching does not require the total removal or depletion of molecular gas, as many quenching models suggest. However, further observations are required both to determine if these apparently quiescent objects host highly obscured star formation and to investigate the intrinsic variation in the molecular gas properties of post-starburst galaxies.

The first few hundred Myrs at z > 10 mark the last major uncharted epoch in the history of the Universe, where only a single galaxy (GNz11 at z ≈ 11) is currently spectroscopically confirmed. Here we present a search for luminous z > 10 galaxies with JWST /NIRCam photometry spanning ≈ 1 − 5µm and covering 49 arcmin 2 from the public JWST Early Release Science programs (CEERS and GLASS). Our most secure candidates are two M UV ≈ −21 systems: GLASS-z13 and GLASS-z11. These galaxies display abrupt 2.5 mag breaks in their spectral energy distributions, consistent with complete absorption of flux bluewards of Lyman-α that is redshifted to z ≈ 13 and z ≈ 11. Lower redshift interlopers such as dusty quiescent galaxies with strong Balmer breaks would be comfortably detected at > 5σ in multiple bands where instead we find no flux. From SED modeling we infer that these galaxies have already built up ∼ 10 9 solar masses in stars over the 300−400 Myrs after the Big Bang. The brightness of these sources enable morphological constraints. Tantalizingly, GLASS-z11 shows a clearly extended exponential light profile, potentially consistent with a disk galaxy of r 50 ≈ 0.7 kpc. These sources, if confirmed, join GNz11 in defying number density forecasts for luminous galaxies based on Schechter UV luminosity functions, which require a survey area > 10× larger than we have studied here to find such luminous sources at such high redshifts. They extend evidence from lower redshifts for little or no evolution in the bright end of the UV luminosity function into the cosmic dawn

The chemical composition of galaxies has been measured out to z ∼ 4. However, nearly all studies beyond z ∼ 0.7 are based on strong-line emission from HII regions within star-forming galaxies. Measuring the chemical composition of distant quiescent galaxies is extremely challenging, as the required stellar absorption features are faint and shifted to near-infrared wavelengths. Here, we present ultra-deep rest-frame optical spectra of five massive quiescent galaxies at z ∼ 1.4, all of which show numerous stellar absorption lines. We derive the abundance ratios [Mg/Fe] and [Fe/H] for three out of five galaxies; the remaining two galaxies have too young luminosity-weighted ages to yield robust measurements. Similar to lower-redshift findings, [Mg/Fe] appears positively correlated with stellar mass, while [Fe/H] is approximately constant with mass. These results may imply that the stellar mass-metallicity relation was already in place at z ∼ 1.4. While the [Mg/Fe]-mass relation at z ∼ 1.4 is consistent with the z < 0.7 relation, [Fe/H] at z ∼ 1.4 is ∼ 0.2 dex lower than at z < 0.7. With a [Mg/Fe] of 0.44 +0.08 −0.07 the most massive galaxy may be more α-enhanced than similar-mass galaxies at lower redshift, but the offset is less significant than the [Mg/Fe] of 0.6 previously found for a massive galaxy at z = 2.1. Nonetheless, these results combined may suggest that [Mg/Fe] in the most massive galaxies decreases over time, possibly by accreting low-mass, less α-enhanced galaxies. A larger galaxy sample is needed to confirm this scenario. Finally, the abundance ratios indicate short star-formation timescales of 0.2 − 1.0 Gyr.

Surveys with James Webb Space Telescope (JWST) have discovered candidate galaxies in the first 400 Myr of cosmic time 1-5 . The properties of these distant galaxies provide initial conditions for understanding early galaxy formation and cosmic reionisation 6 . Preliminary indications have suggested these candidate galaxies may be more massive and abundant than previously thought 1,7-9 . However, without spectroscopic confirmation of their distances to constrain their intrinsic brightnesses, their inferred properties remain uncertain. Here we report on four galaxies located in the JWST Advanced Deep Extragalactic Survey (JADES) Near-Infrared Camera (NIRCam) imaging with photometric redshifts 𝒛 ∼ 𝟏𝟎 − 𝟏𝟑 subsequently confirmed by JADES JWST Near-Infrared Spectrograph (NIRSpec) observations 10 . These galaxies include the first redshift 𝒛 > 𝟏𝟐 systems both discovered and spectroscopically confirmed by JWST. Using stellar population modelling, we find the galaxies typically contain a hundred million solar masses in stars, in stellar populations that are less than one hundred million years old. The moderate star formation rates and compact sizes suggest elevated star formation rate surface densities, a key indicator of their formation pathways. Taken together, these measurements show that the first galaxies contributing to cosmic reionisation formed rapidly and with intense internal radiation fields.

This Letter examines how the sizes, structures, and color gradients of galaxies change along the quiescent sequence. Our sample consists of ∼400 quiescent galaxies at 1.0 ≤ z ≤ 2.5 and in three CANDELS fields. We exploit deep multi-band Hubble Space Telescope imaging to derive accurate mass profiles and color gradients, then use an empirical calibration from rest-frame UVJ colors to estimate galaxy ages. We find that—contrary to previous results—the youngest quiescent galaxies are not significantly smaller than older quiescent galaxies at fixed stellar mass. These “post-starburst” galaxies only appear smaller in half-light radii because they have systematically flatter color gradients. The strength of color gradients in quiescent galaxies is a clear function of age, with older galaxies exhibiting stronger negative color gradients (i.e., redder centers). Furthermore, we find that the central mass surface density Σ1 is independent of age at fixed stellar mass, and only weakly depends on redshift. This finding implies that the central mass profiles of quiescent galaxies do not significantly change with age; however, we find that older quiescent galaxies have additional mass at large radii. Our results support the idea that building a massive core is a necessary requirement for quenching beyond z = 1, and indicate that post-starburst galaxies are the result of a rapid quenching process that requires structural change. Furthermore, our observed color gradient and mass profile evolution supports a scenario where quiescent galaxies grow inside-out via minor mergers.