Low-mass galaxy formation and the ionizing photon budget during reionization

We use high-resolution simulations of cosmological volumes to model galaxy formation at high redshift, with the goal of studying the photon budget for reionization. We demonstrate that galaxy formation models that include a strong, thermally coupled supernovae scheme reproduce current observations of star formation rates and specific star formation rates, both during and after the reionization era. These models produce enough UV photons to sustain reionization at z ≲ 8 (z ≲ 6) through a significant population of faint, unobserved, galaxies for an assumed escape fraction of 20 per cent (5 per cent). This predicted population is consistent with extrapolation of the faint end of observed UV luminosity functions. We find that heating from a global UV/X-ray background after reionization causes a dip in the total global star formation rate density in galaxies below the current observational threshold. Finally, while the currently observed specific star formation rates are incapable of differentiating between supernovae feedback models, sufficiently deep observations will be able to use this diagnostic in the future to investigate galaxy formation at high redshift.