Tracing galaxy growth and Ly [alpha] emission in the early universe

This thesis seeks to understand galaxy formation and evolution in the first three billion years after the Big Bang. Under this goal, studies presented in this thesis consist of several themes, from exploring both individual galaxies using spectroscopic data (Lyα emitters at z ∼ 2.3; Keck/MOSFIRE spectroscopy of z = 7-8 galaxies) and large samples of galaxies using imaging data (galaxy stellar mass function at z = 4-8) to empirical modeling of galaxy evolution over cosmic time. First, we explore the physical origin of Lyα emitters at z ∼ 2.3, analogs to high-redshift galaxies, with near-infrared spectroscopic data. By comparing their properties with typical star-forming galaxies at comparable stellar mass and redshift, we propose that the metallicity may be the key factor discerning these two populations. Second, with the aim of spectroscopically confirming galaxies at z [greater than approximately] 7 as well as placing constraints on the neutrality of intergalactic medium, we conduct deep spectroscopic campaign for z = 7-8 galaxy candidates. We report the discovery of Lyα emission at z = 7.66, which marks the third most distant spectroscopically confirmed galaxy via Lyα. Subsequent chapters are devoted to exploring the galaxy stellar mass growth history over cosmic time. This consists of two studies; first, observationally constraining the galaxy stellar mass function at z = 4-8 using deep Hubble and Spitzer Space Telescope data, and second, building an empirical model of galaxy evolution out to z = 8 by combining abundance matching techniques with the dark matter halo growth history extracted from cosmological simulation.