The Universe is at Most 88% Neutral at z = 10.6

Abstract

Recent observations of GN-z11 with JWST have revealed a Lyα emission line with an equivalent width (EW) of 18 ± 2 Å. 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, x H I. We use these distributions to place an upper limit of x H I < 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 a higher escape fraction compared to bright galaxies are favored by the new data.