Two Remarkably Luminous Galaxy Candidates at z ≈ 10–12 Revealed by JWST

Abstract

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 arcmin ² 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 Ly α 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 >5 σ 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 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.