Probing an Inhomogeneity of Reionization with a Deep and Wide Lyman-alpha Emission Survey

Reionization of the intergalactic medium (IGM) marks the time in the early universe when the first stars and galaxies began to affect the universe around them, thus studying reionization can provide key insights into the formation and evolution of galaxies in the early universe. As Lyman-alpha photons are resonantly scattered by neutral hydrogen in the IGM, an analysis of this line can be used to trace the existence of neutral hydrogen in the IGM at different points in the history of the universe. Spectroscopic data of galaxies in the early universe, obtained with the DEIMOS (optical) and MOSFIRE (near-infrared; NIR) spectrographs on the Keck telescopes, is utilized for investigating the evolution of the IGM during reionization by measuring the Lyman-alpha equivalent width (EW) distribution. I will present the results of our spectroscopic analysis on the Lyman-alpha EW distribution, the Lyman-alpha transmission in the IGM, and the inferred IGM neutral fraction at z ~ 7.6. This reveals a highly-ionized structure at this redshift, providing additional evidence of inhomogeneous nature of reionization during the middle phase of reionization. Such inhomogeneity of reionization presented here demonstrates that future studies with much wider-field Lyman-alpha surveys, which can be accomplished with the Nancy Grace Roman Space Telescope, will better capture the global evolution of reionization