Cosmic reionization by stellar sources: population III stars

We combine fast radiative transfer calculations with high‐resolution hydrodynamical simulations to study an epoch of early hydrogen reionization by primordial stellar sources at redshifts 15 ≲z≲ 30. We consider the implications of various local and global feedback mechanisms using a set of models that bracket the severity of these effects to determine, qualitatively, how they may have influenced the global star formation rate and the details of hydrogen reionization. With relatively conservative assumptions, most of our models suggest that population III star formation proceeds in a self‐regulated manner both locally and globally and, for a conventional ΛCDM cosmology, can significantly reionize the intergalactic medium between 15 ≲z≲ 20 as long as a large fraction of ionizing photons can escape from these earliest galaxies. We then combine these results with our earlier work focusing on the role of population II stars in galaxies with virial temperatures ≳104 K at redshifts 5 ≲z≲ 20. Hence, we construct a complete reionization history of the Universe that matches the Thomson optical depths as measured by the WMAP satellite as well as the evolution of the Gunn–Peterson optical depth as seen in the absorption spectra of the highest redshift quasars. We find that even with conservative estimates for the impact of negative feedback mechanisms, primordial stellar sources contribute significantly to early reionization. Future observations of a Thomson optical depth of τe≳ 0.13 would bolster the claim for the existence of population III stars similar to the ones studied here.