JADES: The emergence and evolution of Ly<i>α</i> emission and constraints on the intergalactic medium neutral fraction
Gareth C. Jones, Andrew J. Bunker, Aayush Saxena, Joris Witstok, Daniel P. Stark, Santiago Arribas, William Baker, Rachana Bhatawdekar, R. A. A. Bowler, Kristan Boyett, Alex J. Cameron, Stefano Carniani, S. Charlot, Jacopo Chevallard, Mirko Curti, Emma Curtis-Lake, Daniel J. Eisenstein, Kevin Hainline, Ryan Hausen, Zhiyuan Ji, Benjamin D. Johnson, Nimisha Kumari, Tobias J. Looser, R. Maiolino, Michael V. Maseda, Eleonora Parlanti, Hans‐Walter Rix, Brant Robertson, Lester Sandles, Jan Scholtz, Renske Smit, Sandro Tacchella, Hannah Übler, Christina C. Williams, Chris J. Willott
Abstract
The rest-frame UV recombination emission line Ly α can be powered by ionising photons from young massive stars in star-forming galaxies, but the fact that it can be resonantly scattered by neutral gas complicates its interpretation. For reionisation-era galaxies, a neutral intergalactic medium will scatter Ly α from the line of sight, making Ly α a useful probe of the neutral fraction evolution. Here, we explore Ly α in JWST/NIRSpec spectra from the ongoing JADES programme, which targets hundreds of galaxies in the well-studied GOODS-S and GOODS-N fields. These sources are UV-faint (−20.4 < M UV < −16.4) and thus represent a poorly explored class of galaxy. We fitted the low spectral resolution spectra ( R ∼ 100) of a subset of 84 galaxies in GOODS-S with z spec > 5.6 (as derived with optical lines) with line and continuum models to search for significant line emission. Through exploration of the R100 data, we find evidence for Ly α in 17 sources. This sample allowed us to place observational constraints on the fraction of galaxies with Ly α emission in the redshift range 5.6 < z < 7.5, with a decrease from z = 6 to z = 7. We also find a positive correlation between the Ly α equivalent width and M UV , as seen in other samples. We used these results to estimate the neutral gas fraction at z ∼ 7, and our estimates are in agreement with previous results ( X HI ∼ 0.5 − 0.9).