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 (1σ uncertainty) with m F200W = 27.3 and ≳7σ detections in five filters. The source is not detected at λ < 1.4 μm in deep imaging from both Hubble Space Telescope (HST) and JWST and has faint ∼3σ detections in JWST F150W and HST F160W, which signal a Lyα break near the red edge of both filters, implying z ∼ 12. This object (Maisie’s Galaxy) exhibits F115W − F200W > 1.9 mag (2σ 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.

We use deep Hubble Space Telescope spectroscopy to constrain the metallicities and (light-weighted) ages of massive (log M * /M 10) galaxies selected to have quiescent stellar populations at 1.0 < z < 1.8. The data include 12-orbit depth coverage with the WFC3/G102 grism covering ∼ 8, 000 < λ < 11, 500 Å at a spectral resolution of R ∼ 210 taken as part of the CANDELS Lyman-α Emission at Reionization (CLEAR) survey. At 1.0 < z < 1.8, the spectra cover important stellar population features in the rest-frame optical. We simulate a suite of stellar population models at the grism resolution, fit these to the data for each galaxy, and derive posterior likelihood distributions for metallicity and age. We stack the posteriors for subgroups of galaxies in different redshift ranges that include different combinations of stellar absorption features. Our results give light-weighted ages of t z∼1.1 = 3.2 ± 0.7 Gyr, t z∼1.2 = 2.2 ± 0.6 Gyr, t z∼1.3 = 3.1 ± 0.6 Gyr, and t z∼1.6 = 2.0 ± 0.6 Gyr, for galaxies at z ∼ 1.1, 1.2, 1.3, and 1.6. This implies that most of the massive quiescent galaxies at 1 < z < 1.8 had formed > 68% of their stellar mass by a redshift of z > 2. The posteriors give metallicities of Z z∼1.1 = 1.16 ± 0.29 Z , Z z∼1.2 = 1.05 ± 0.34 Z , Z z∼1.3 = 1.00 ± 0.31 Z , and Z z∼1.6 = 0.95 ± 0.39 Z . This is evidence that massive galaxies had enriched rapidly to approximately Solar metallicities as early as z ∼ 3.

We report on the gas-phase metallicity gradients of a sample of 238 star-forming galaxies at 0.6 < z < 2.6, measured through deep near-infrared Hubble Space Telescope slitless spectroscopy. The observations include 12 orbit depth Hubble/WFC3 G102 grism spectra taken as a part of the CANDELS Lyα Emission at Reionization (CLEAR) survey, and archival WFC3 G102+G141 grism spectra overlapping the CLEAR footprint. The majority of galaxies in this sample are consistent with having a zero or slightly positive metallicity gradient (dZ/dR ≥ 0, i.e., increasing with radius) across the full mass range probed (8.5 < log M */M ⊙ < 10.5). We measure the intrinsic population scatter of the metallicity gradients, and show that it increases with decreasing stellar mass—consistent with previous reports in the literature, but confirmed here with a much larger sample. To understand the physical mechanisms governing this scatter, we search for correlations between the observed gradient and various stellar population properties at fixed mass. However, we find no evidence for a correlation with the galaxy properties we consider—including star formation rates, sizes, star formation rate surface densities, and star formation rates per gravitational potential energy. We use the observed weakness of these correlations to provide material constraints for predicted intrinsic correlations from theoretical models.