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

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 asymptotic to 11) is currently spectroscopically confirmed. Here we present a search for luminous z > 10 galaxies with JWST/NIRCam photometry spanning asymptotic to 1-5 mu m and covering 49 arcmin(2) from the public JWST Early Release Science programs (CEERS and GLASS). Our most secure candidates are two M-UV asymptotic to -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 alpha that is redshifted to z 12.4 -(+ 0.1)(0.3) and z = 10.4 (+0.4)(-0.5). Lower redshift interlopers such as quiescent galaxies with strong Balmer breaks would be comfortably detected at > 5 sigma in multiple bands where instead we find no flux. From SED modeling we infer that these galaxies have already built up similar to 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) asymptotic to 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 > 10x 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.

Automated summary

Researchers have used JWST/NIRCam to search for bright galaxies in the last unexplored epoch of the universe (around a few hundred million years ago with z > 10). They have identified two candidate galaxies, which show spectral features suggesting they may have formed stars with a mass of around 10^9 solar masses in approximately 300-400 million years. These findings challenge previous predictions of the number density of such bright sources at high redshifts.