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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 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).
Jones et al. (Wed,) studied this question.
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