| In this Thesis, I study of the formation and the evolution of the first galaxies. The theory of galaxy formation predicts that the creation process is hierarchical: small objects form first, and large galaxies form later from mergers of smaller subunits. The first galaxies are believed to have formed 100 million years after the Big Bang, at redshift z ∼ 30. In these primordial galaxies, the first stars emitted light into a previously dark universe. The radiation emitted at this time influenced the subsequent evolution of the universe in a still-unknown way. This process of self-regulation, in which the radiation emitted by galaxies influenced the surrounding intergalactic medium and the future formation of other galaxies, is termed “radiative feedback” from galaxy formation. We find that the first luminous objects (Population III) are characterized by a bursting star formation that is self-regulated by a feedback process acting on cosmological scale. The global star formation history is regulated by the fraction, ⟨fesc⟩, of ionizing photons that escape from each source. The main feedback processes that regulate Population III objects formation are H2 formation in front of H II regions and inside relic H II regions. The H II regions remain confined, producing a cyclic destruction/reformation of H2 in the dense regions that are the birthplaces of galaxies. If ⟨fesc ⟩ < 0.01, positive feedback dominates, and Population III objects constitute the bulk of the mass in stars and metals until redshift z ∼10. In contrast to massive objects, which reionize voids first, Population III objects partially ionize only the dense filaments, while leaving the voids neutral. |
