The Fate of the First Galaxies. II. Effects of Positive Feedback on Population III Objects

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  • 18 October 2001
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 (Population III) 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, \epsilon_{UV}\fesc. It is almost independent of the assumed star formation efficiency parameter, \epsilon_*, 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 \epsilon_{UV}\fesc > 10^{-8}/\epsilon_* the SF is self-regulated, photo-evaporation of Population III objects dominate the metal pollution of the low density IGM, and the mass of produced metals depends only on \fesc. If \epsilon_{UV}\fesc \simlt 10^{-8}/\epsilon_*, positive feedback dominates, and Population III objects constitute the bulk of the mass in stars and metals at least until redshift z \sim 10. Population III 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, Population III objects partially ionize only the dense filaments while leaving the voids neutral.

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