Presentation #207.05 in the session Evolution of Galaxies III.
Reionization is an inhomogeneous process, thought to begin in small ionized bubbles of the intergalactic medium (IGM) around overdense regions of galaxies. Recent Lyman-alpha studies during the epoch of reionization show evidence that ionized bubbles formed earlier around brighter galaxies, suggesting higher IGM transmission of Lyman-alpha 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 Lyman-alpha Emission at Reionization (CLEAR) survey. We combine the CLEAR data for 275 galaxies with the Keck/DEIMOS+MOSFIRE dataset from the Texas Spectroscopic Search for Lyman-alpha Emission at the End of Reionization Survey. We constrain the Lyman-alpha equivalent-width (EW) distribution at 6.0 < z < 8.2. We confirm a significant drop of the Lyman-alpha strength at z > 6. Furthermore, we compare the redshift evolution of the Lyman-alpha EW distribution between galaxies at different UV luminosities. UV-bright (MUV < -21 [i.e., LUV > L*]) galaxies show weaker evolution at z > 6 while UV-faint (MUV > -21 [LUV < L*]) galaxies exhibit a significant drop in the Lyman-alpha strength from z < 6 to z > 6. If the change is proportional to the change in the IGM transmission for Lyman-alpha photons, then this is evidence that the transmission is boosted around UV-brighter galaxies, suggesting that reionization proceeds faster in regions around such galaxies.