The Lyman-alpha signature of the first galaxies

This dissertation is presented as a collection of projects related to the first galaxies and supermassive black holes. The analysis centers around the Lyman α (Lyα) line of atomic hydrogen, which is an especially powerful probe of the high-redshift universe due to its characteristic strength and spectral properties. Several instruments and telescopes have recently been or will be targeting the Lyα line with significantly increased sensitivity across all redshifts. In light of such advances, we continue to be optimistic that when combined with other observational signatures, accurate Lyα modeling can reveal key physical properties about the intrinsic sources and external environments of these systems. The included works incorporate state-of-the-art radiation transport calculations within high resolution ab initio cosmological simulations or more idealized setups to understand the imprint of galaxy formation during the first billion years after the Big Bang. Each chapter is a self-contained project with the title corresponding to a peer-reviewed publication. The collection includes significant discussion of code development, analysis methods, specific applications, likely interpretations, and broad perspectives that will hopefully benefit future researchers in this field, as we observe and model the universe with ever increasing realism.