We present a new measurement of the Lyα luminosity function at redshift z=6.9, finding moderate evolution from z=5.7 that is consistent with a fully or largely ionized z∼7 intergalactic medium. Our result is based on four fields of the LAGER (Lyman Alpha Galaxies in the Epoch of Reionization) project. Our survey volume of 6.1×106 Mpc3 is double that of the next largest z∼7 survey. We combine two new LAGER fields (WIDE12 and GAMA15A) with two previously reported LAGER fields (COSMOS and CDFS). In the new fields, we identify N=95 new z=6.9 Lyα emitters (LAEs); characterize our survey's completeness and reliability; and compute Lyα luminosity functions. The best-fit Schechter luminosity function parameters for all four LAGER fields are in good general agreement. Two fields (COSMOS and WIDE12) show evidence for a bright-end excess above the Schechter function fit. We find that the Lyα luminosity density declines at the same rate as the UV continuum LF from z=5.7 to z=6.9. This is consistent with an intergalactic medium that was fully ionized as early as redshift z∼7, or with a volume-averaged neutral hydrogen fraction of xHI<0.33 at 1σ.
@article{arxiv.2105.12191,
title = {LAGER Ly$\alpha$ Luminosity Function at $z\sim7$, Implications for Reionization},
author = {Isak G. B. Wold and Sangeeta Malhotra and James Rhoads and Junxian Wang and Weida Hu and Lucia A. Perez and Zhen-Ya Zheng and Ali Ahmad Khostovan and Alistair R. Walker and L. Felipe Barrientos and Jorge González-López and Santosh Harish and Leopoldo Infante and Chunyan Jiang and John Pharo and Cristóbal Moya-Sierralta and Franz E. Bauer and Gaspar Galaz and Francisco Valdes and Huan Yang},
journal= {arXiv preprint arXiv:2105.12191},
year = {2022}
}