The Fate of the First Galaxies. Ii. Effects of Positive Feedback on Population Iii Objects


We use 3D cosmological simulations with radiative transfer to study the formation and evolution of the first galaxies in a ΛCDM cosmology. The simulations include continuum radiative transfer using the “Optically Thin Variable Eddington Tensor” (OTVET) approximation and line-radiative transfer in the H2 Lyman-Werner bands of the background radiation. Chemical and thermal processes are treated in detail, particularly the ones relevant for H2 formation and destruction. 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, ǫUV 〈fesc〉. It is almost independent of the assumed star formation efficiency parameter, ǫ∗, and the intensity of the dissociating background. The main feedback process that regulates the SF is the re-formation of H2 in front of H ii regions and inside relic H ii regions. The H ii regions remain confined inside filaments, maximizing the production of H2 in overdense regions through cyclic destruction/reformation of H2. If ǫUV 〈fesc〉 > 10 /ǫ∗ 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 ǫUV 〈fesc〉 < ∼ 10 /ǫ∗, positive feedback dominates, and Population III objects constitute the bulk of the mass in stars and metals at least until redshift z ∼ 10. Population III objects cannot reionize the universe because the feedback mechanism confines the H ii 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. Subject headings: Cosmology: early universe—cosmology: theory—galaxies: dwarf— galaxies: evolution—galaxies: formation—galaxies: high-redshift—intergalactic medium— methods: numerical DRAFT: March 15, 2008 2

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@inproceedings{Ricotti2001TheFO, title={The Fate of the First Galaxies. Ii. Effects of Positive Feedback on Population Iii Objects}, author={Massimo Ricotti and Nickolay Y. Gnedin}, year={2001} }