CLEAR: Boosted Lyα Transmission of the Intergalactic Medium in UV-bright Galaxies

Reionization is an inhomogeneous process, thought to begin in small ionized bubbles of the intergalactic medium (IGM) around overdense regions of galaxies. Recent Ly α studies during the epoch of reionization show evidence that ionized bubbles formed earlier around brighter galaxies, suggesting higher IGM transmission of Ly α from these galaxies. We investigate this problem using IR slitless spectroscopy from the Hubble Space Telescope (HST) Wide-Field Camera 3 (WFC3) G102 grism observations of 148 galaxies selected via photometric redshifts at 6.0 < z < 8.2. These galaxies have spectra extracted from the CANDELS Ly α Emission at Reionization (CLEAR) survey. We combine the CLEAR data for 275 galaxies with the Keck Deep Imaging Multi-Object Spectrograph and MOSFIRE data set from the Texas Spectroscopic Search for Ly α Emission at the End of Reionization Survey. We constrain the Ly α equivalent width (EW) distribution at 6.0 < z < 8.2, which is described by an exponential form, dN / d EW ∝ exp ( − EW ) / W 0 , with the characteristic e -folding scale width ( W 0 ). We confirm a significant drop in the Ly α strength (i.e., W 0 ) at z > 6. Furthermore, we compare the redshift evolution of W 0 between galaxies at different UV luminosities. UV-bright ( M UV < −21 [i.e., L UV > L *]) galaxies show weaker evolution with a decrease of 0.4 ( ± 0.2) dex in W 0 at z > 6, while UV-faint ( M UV > −21 [ L UV < L *]) galaxies exhibit a significant drop of 0.7–0.8 (±0.2) dex in W 0 from z < 6 to z > 6. If the change in W 0 is proportional to the change in the IGM transmission for Ly α photons, then this is evidence that the transmission is “boosted” around UV-brighter galaxies, suggesting that reionization proceeds faster in regions around such galaxies.