Ly Emission at : Clear Ly Equivalent Width Evolution Indicating the Late Cosmic Reionization History
arXiv:2312.06804
Abstract
We present the evolution of Ly emission derived from 53 galaxies at that are identified by multiple JWST/NIRSpec spectroscopy programs of ERS, GO, DDT, and GTO. These galaxies fall on the star-formation main sequence and are the typical star-forming galaxies with UV magnitudes of . We find that 15 out of 53 galaxies show Ly emission at the levels, and obtain Ly equivalent width (EW) measurements and stringent upper limits for the 15 and 38 galaxies, respectively. Confirming that Ly velocity offsets and line widths of our galaxies are comparable with those of low-redshift Ly emitters, we investigate the redshift evolution of the Ly EW. We find that Ly EWs statistically decrease towards high redshifts on the Ly EW vs. plane for various probability distributions of the uncertainties. We then evaluate neutral hydrogen fractions with the Ly EW redshift evolution and the cosmic reionization simulation results on the basis of a Bayesian inference framework, and obtain , , and at , , and , respectively. These moderately large values are consistent with the Planck CMB optical depth measurement and previous constraints from galaxy and QSO Ly damping wing absorptions, and strongly indicate a late reionization history. Such a late reionization history suggests that major sources of reionization would emerge late and be hosted by moderately massive halos in contrast with the widely-accepted picture of abundant low-mass objects for the sources of reionization.
Accepted for publication in ApJ