Modeling of Galaxy and Massive Black Hole Evolution Since Cosmic Dawn

 This thesis explores the evolution of galaxies and massive black holes (MBHs) since cosmic dawn, focusing on cosmic reionization and MBH binaries. I develop and employ novel numerical methods for more accurate modeling of cosmic reionization and MBH binaries to better understand these processes, and for putting astrophysical constraints with ongoing and future observations. Cosmic reionization starts with the formation of the first galaxies and influences all the baryon components in the Universe. I develop and apply semi-numerical algorithms to better understand the timing and duration of cosmic reionization, as well as its spatial progression, with current observational constraints from the cosmic wave background. Massive black hole binaries offer another promising channel for understanding the Universe since the first galaxies formed. I advance the modeling of the massive black hole binary population in cosmological simulations of galaxy formation. This leads to a more accurate characterization of the MBH binary population across all redshift and mass ranges. I investigated the binary evolution in realistic galaxy environments and made theoretical predictions for the ongoing and upcoming electromagnetic and gravitational wave observations of these binaries. These predictions can be useful in interpreting observations and constraining MBH seeds, growth and assembly histories. My study of cosmic reionization and MBH binaries constitutes theoretical progress in understanding several aspects of galaxy formation, especially in the high-redshift Universe.