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JADES: The emergence and evolution of Ly α emission and constraints on the intergalactic medium neutral fraction

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jats:pThe rest-frame UV recombination emission line Lyjats:italicα</jats:italic> 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 Lyjats:italicα</jats:italic> from the line of sight, making Lyjats:italicα</jats:italic> a useful probe of the neutral fraction evolution. Here, we explore Lyjats:italicα</jats:italic> 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 < jats:italicM</jats:italic>jats:subUV</jats:sub> < −16.4) and thus represent a poorly explored class of galaxy. We fitted the low spectral resolution spectra (jats:italicR</jats:italic> ∼ 100) of a subset of 84 galaxies in GOODS-S with jats:italicz</jats:italic>jats:subspec</jats:sub> > 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 Lyjats:italicα</jats:italic> in 17 sources. This sample allowed us to place observational constraints on the fraction of galaxies with Lyjats:italicα</jats:italic> emission in the redshift range 5.6 < jats:italicz</jats:italic> < 7.5, with a decrease from jats:italicz</jats:italic> = 6 to jats:italicz</jats:italic> = 7. We also find a positive correlation between the Lyjats:italicα</jats:italic> equivalent width and jats:italicM</jats:italic>jats:subUV</jats:sub>, as seen in other samples. We used these results to estimate the neutral gas fraction at jats:italicz</jats:italic> ∼ 7, and our estimates are in agreement with previous results (jats:italicX</jats:italic>jats:subHI</jats:sub> ∼ 0.5 − 0.9).</jats:p>



5101 Astronomical Sciences, 51 Physical Sciences

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Astronomy and Astrophysics

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EDP Sciences
European Research Council (695671)