Cosmological Reionization Around the First Stars: Monte Carlo Radiative Transfer

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Abstract
We study the evolution of ionization fronts around the first stars by combining high resolution numerical cosmological (Lambda+CDM model) simulations and Monte Carlo radiative transfer methods. In particular, we follow the reionization produced by a stellar source of total mass M=2 \times 10^8 M_\odot which turns on at z=12, located at a node of the cosmic web. We explore the role of (i) the Spectral Energy Distribution of a zero-metallicity stellar population, (ii) two Initial Mass Functions (Salpeter/Larson), and (iii) intergalactic medium density inhomogeneities. The expansion of the I-front is efficiently and accurately described by the Monte Carlo scheme as it breaks out from the galaxy and it is channeled by the filaments into the voids, assuming a characteristic butterfly shape. For a Salpeter IMF, the volume of the ionized region is smaller by a factor ~10. We conclude that both the shape of the IMF and the ionizing power metallicity dependence are important to determine the reionization of the universe.

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