The fate of the first galaxies. I. Self-consistent cosmological simulations with radiative transfer

In cold dark matter (CDM) cosmogonies, low-mass objects play an important role in the evolution of the universe. Not only are they the first luminous objects to shed light in a previously dark universe, but if their formation is not inhibited by their own feedback, they dominate the galaxy mass function until redshift z similar to 5. In this paper we present and discuss the implementation of a three-dimensional cosmological code that includes most of the needed physics to simulate the formation and evolution of the first galaxies with a self-consistent treatment of radiative feedback. The simulation includes continuum radiative transfer using the optically thin variable Eddington tensor (OTVET) approximation and line radiative transfer in the H-2 Lyman-Werner bands of the background UV radiation. We include detailed chemistry for H-2 formation/ destruction, molecular and atomic cooling/heating processes, ionization by secondary electrons, and heating by Lyalpha resonant scattering. We find that the first galaxies (small-halo galaxies) are characterized by bursting star formation, self-regulated by a feedback process that acts on cosmological scales. The mass in stars produced by these objects can exceed the mass in stars produced by normal galaxies; therefore, their impact on cosmic evolution cannot be neglected. The main focus of this paper is on the methodology of the simulations, and we only briefly introduce some of the results. An extensive discussion of the results and the nature of the feedback mechanism are the focus of a companion paper.