We present the evolution of Lyα emission derived from 53 galaxies at z=6.6−13.2 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 −22.5≤MUV≤−17.0. We find that 15 out of 53 galaxies show Lyα emission at the >3σ levels, and obtain Lyα equivalent width (EW) measurements and stringent 3σ upper limits for the 15 and 38 galaxies, respectively. Confirming that Lyα velocity offsets and line widths of our galaxies are comparable with those of low-redshift Lyα emitters, we investigate the redshift evolution of the Lyα EW. We find that Lyα EWs statistically decrease towards high redshifts on the Lyα EW vs. MUV plane for various probability distributions of the uncertainties. We then evaluate neutral hydrogen fractions xHI with the Lyα EW redshift evolution and the cosmic reionization simulation results on the basis of a Bayesian inference framework, and obtain xHI<0.79, =0.62−0.36+0.15, and 0.93−0.07+0.04 at z∼7, 8, and 9−13, respectively. These moderately large xHI values are consistent with the Planck CMB optical depth measurement and previous xHI constraints from galaxy and QSO Lyα 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.
@article{arxiv.2312.06804,
title = {Ly$\alpha$ Emission at $z=7-13$: Clear Ly$\alpha$ Equivalent Width Evolution Indicating the Late Cosmic Reionization History},
author = {Minami Nakane and Masami Ouchi and Kimihiko Nakajima and Yuichi Harikane and Yoshiaki Ono and Hiroya Umeda and Yuki Isobe and Yechi Zhang and Yi Xu},
journal= {arXiv preprint arXiv:2312.06804},
year = {2024}
}