James Webb Space Telescope Feed Post

Harvard ADS: JADES: Measuring reionization properties using Lyman-alpha emission

Paper 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 which show 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 characterise Ly\alpha emitting galaxies (LAEs). This survey is now approaching completion, and the current sample is nearly an order of magnitude larger. From a sample of 784 galaxies in JADES at 4.0 < z < 14.3, we find evidence for Ly\alpha emission in 145 sources. We reproduce the previously found correlation between Ly\alpha escape fraction (\fesc) - Ly\alpha rest-frame equivalent width (\rew) and the negative correlation between Ly\alpha velocity offset - \fesc. Both \fesc and \rew decrease with redshift (z\gtrsim5.5), indicating the progression of reionization on a population scale. Our data are used to demonstrate an increasing IGM transmission of Ly\alpha from z~14-6. We measure the completeness-corrected fraction of LAEs (X_{Ly\alpha}) from z=4-9.5. An application of these X_{Ly\alpha} values to the results of cosmological models suggests a high neutral fraction at z=7 (\rm X_{HI}=0.81_{-0.10}^{+0.07}), likely suggesting the need for models with updated \rew distributions (based on comparison to other works). This large sample of LAEs and the completeness correction we have detailed will be paramount for unbiased population studies of galaxies in the EoR.