JADES: measuring reionization properties using Lyman-alpha emission

Abstract

Ly\alpha is the transition to the ground state from the first excited state of hydrogen (the most common element). Resonant scattering of this line by neutral hydrogen greatly impedes its emergence from galaxies, so the fraction of galaxies emitting Ly\alpha is a tracer of the neutral fraction of the intergalactic medium (IGM), and thus the history of reionization. In previous works, we used early JWST/NIRSpec data from the JWST Advanced Deep Extragalactic Survey (JADES) to classify and characterize Ly\alpha emitting galaxies (LAEs). This survey is approaching completion, and the current sample is nearly an order of magnitude larger. From a sample of 795 galaxies in JADES at 4.0\lt z\4.3, we find evidence for Ly\alpha emission in 150 sources. We reproduce the previously found correlation between Ly\alpha escape fraction (f\rm esc^Ly\alpha ) – Ly\alpha rest-frame equivalent width (\rm REW\rm Ly\alpha ) and the negative correlation between Ly\alpha velocity offset – f\rm esc^Ly\alpha . Both f\rm esc^Ly\alpha and \rm REW\rm Ly\alpha decrease with redshift (z\.5), indicating the progression of reionization on a population scale. Our data are used to demonstrate an increasing IGM transmission of Ly\alpha from z\4-6. We measure the completeness-corrected fraction of LAEs (X\rm Ly\alpha ) from z=4-9.5. An application of these X\rm Ly\alpha values to the results of previously utilized semi-analytical models suggests a high neutral fraction at z=7 (X\rm HI\.8-0.9). Using an updated fit to the intrinsic distribution of \rm REW\rm Ly\alpha results in a lower value in agreement with current works (X\rm HI= 0.64-0.21^+0.13). This sample of LAEs will be paramount for unbiased population studies of galaxies in the EoR.