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Abstract

Lyman-alpha (Ly-a) absorption features detected in quasar spectra in the redshift range 0<z<6 are a powerful tool to probe the intergalactic and circumgalactic media (IGM and CGM) and, consequently, to constrain models of galaxy formation and cosmology. In the first part of this thesis, I overcome certain numerical challenges posed by cosmological hydrodynamic simulations by developing a novel semi-analytic technique to predict various statistics of the Ly-a absorption in the IGM with large N-body cosmological simulations. The technique developed in this work is more accurate than previous attempts in the literature. More importantly, it can be applied on Gpc-scale N-body simulations, allowing an accurate investigation of the Ly-a absorption at unprecedentedly large scales. In the second part of the thesis, I consider observations of Ly-a absorption in spectra of background quasars at different transverse separations (between 25 kpc and 17 Mpc) from foreground galaxies, and compare them with the predictions of different state-of-the-art hydrodynamic cosmological simulations. For the first time, I show that combining observations of Ly-a absorption in the IGM and the CGM can tightly constrain the models of sub-resolution physical processes implemented in simulations (e.g., feedback). With near-future high-precision observations of Ly-a absorption, the tools developed in this work will set the stage for even stronger constraints on models of galaxy formation and cosmology.