The Fate of the First Galaxies. II. Effects of Radiative Feedback

Abstract

[abridged]We use 3D cosmological simulations with radiative transfer to study the formation and evolution of the first galaxies in a LCDM cosmology. We find that the first luminous objects ("small-halos") are characterized by a bursting star formation (SF) that is self-regulated by a feedback process acting on cosmological instead of galactic scales. The global star formation history is regulated by the mean number of ionizing photons that escape from each source, ε_{UV}\fesc. It is almost independent of the assumed star formation efficiency parameter, ε_*, and the intensity of the dissociating background. The main feedback process that regulates the SF is the re-formation of H_2 in front of HII regions and inside relic HII regions. The HII regions remain confined inside filaments, maximizing the production of H_2 in overdense regions through cyclic destruction/reformation of H_2. If ε_{UV}\fesc > 10^{-8}/ε_* the SF is self-regulated, photo-evaporation of "small-halo" objects dominate the metal pollution of the low density IGM, and the mass of produced metals depends only on \fesc. If ε_{UV}\fesc \simlt 10^{-8}/ε_*, positive feedback dominates, and "small-halo" objects constitute the bulk of the mass in stars and metals at least until redshift z \sim 10. "Small-halo" objects cannot reionize the universe because the feedback mechanism confines the HII regions inside the large scale structure filaments. In contrast to massive objects, which can reionize voids, "small-halo" objects partially ionize only the dense filaments while leaving the voids mostly neutral.