The nature of low-luminosity galaxies and their role during reionization

I present results from a suite of cosmological radiation hydrodynamics simulations that focus on the transition from Population III star formation to the first galaxies. Each simulation captures the radiative and chemical feedback from ~300 Population III stars, leading to the formation of a 10^9 solar mass galaxy at redshift 7. We find that Population III stars enrich all galaxies to minimum metallicity of [Z/H] = -3 to -4. We show that momentum transfer from ionizing radiation plays an important role in providing turbulent support and mixing metals, preventing the overproduction of stars and metals. This results in a stellar population with a tight metallicity distribution function centered at [Z/H] = -2, agreeing with the observed luminosity-metallicity relation in dwarf galaxies. Furthermore, we find that the UV escape fraction from low-luminosity galaxies is higher than 10% and that they contribute the majority of ionizing radiation during reionization.