Escape Fractions from Unattenuated Ly α Emitters around Luminous z > 6 Quasars

Ionized proximity zones around luminous quasars provide a unique laboratory to characterize the Ly α emission lines from z > 6 galaxies without significant attenuation from the intergalactic medium (IGM). However, Ly α line measurements for galaxies within high-redshift quasars’ proximity zones have been rare so far. Here we present deep spectroscopic observations obtained with the NIRSpec/Micro-Shutter Assembly (MSA) instrument on the James Webb Space Telescope of galaxies in two z > 6 quasar fields. We measure the Ly α line fluxes for 50 galaxies at 6 < z < 7 with UV absolute magnitude M UV < −19 (median M UV = −19.97), among which 15 are located near the luminous quasars, i.e., within Δ v < 2500 km s −1 . We find that galaxies near the quasars show significant flux blueward of the systemic Ly α wavelength, and have higher Ly α equivalent width compared to galaxies at similar redshifts that are not located within the quasars’ environment. Our result indicates little or no redshift evolution for the Ly α emitter fraction from z ∼ 6.4 to z ∼ 5. Leveraging the low IGM opacity in the quasars’ vicinity, we evaluate the Ly α escape fraction ( f esc Ly α ) of high-redshift galaxies. Our analysis suggests that galaxies at 〈 z 〉 ≈ 6.4 have an average f esc Ly α = 0.14 ± 0.04 . This value is consistent with reionization models where the Lyman continuum escape fraction is low ( f esc LyC ≲ 0.1 ) for luminous galaxies, and where the most luminous galaxies have only a minor contribution to the total ionizing photon budget.