Recent observations of GN-z11 with JWST have revealed a Lyα emission line with an equivalent width of 18±2 angstroms. At z=10.6, this galaxy is expected to lie in the heart of reionization. We use a series of inhomogeneous reionization simulations to derive the distribution of the Lyα EW after traveling through the neutral intergalactic medium with varying average neutral gas fraction, xHI. We use these distribution to place an upper limit of xHI< 0.88 at z=10.6 at 95% confidence level. We compare our upper limit to different reionization history models, which include the recently identified enhancement at the bright end of the luminosity function at z>8. We find that models in which faint galaxies have higher escape fraction compared to bright galaxies are favored by the new data.
@article{arxiv.2303.03419,
title = {The Universe is at Most 88% Neutral at z=10.6},
author = {Sean Bruton and Yu-Heng Lin and Claudia Scarlata and Matthew J. Hayes},
journal= {arXiv preprint arXiv:2303.03419},
year = {2023}
}