Tracing the Ionization State of the Intergalactic Medium with Lyman-alpha during the Epoch of Reionization

As reionization is inherently coupled with galaxies —the dominant sources of ionizing photons— understanding galaxy evolution in the early universe relies on understanding the process of reionization. Lyman-alpha emission has played a pivotal role in constraining the neutral hydrogen (HI) fraction of the intergalactic medium (IGM) during the epoch of reionization (EoR) thanks to the resonant nature of Lyman-alpha scattering with HI. A spectroscopic dataset of galaxies in the early universe, obtained by the DEIMOS (optical) and MOSFIRE (near-infrared; NIR) spectrographs on the Keck telescopes, is utilized for investigating the evolution of the IGM during EoR by measuring the Lyman-alpha equivalent width (EW) distribution. I will present the results of the spectroscopic analysis, including our IGM HI fraction measurement and the discovery of a highly ionized region at z ~ 7.6, which highlights the inhomogeneity of reionization. I will also discuss future directions for improving the use of Lyman-alpha as a probe of reionization.