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

Presentation #207.05 in the session Evolution of Galaxies III.

Published onJun 29, 2022
CLEAR: Boosted Lyman-alpha 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 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.

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