Cosmic Reionisation by Stellar Sources: Population III Stars

We combine fast radiative transfer calculations with high resolution hydrodynamical simulations to study an epoch of early hydrogen reionisation by primordial stellar sources at redshifts 15<z<30. With relatively conservative assumptions, population III star formation proceeds in a self-regulated manner both locally and globally and, for a conventional LCDM cosmology, can significantly reionise the intergalactic medium between 15<z<20 as long as a large fraction of ionising 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 >10^4K at redshifts 5<z< 20. Hence, we construct a complete reionisation history of the Universe which 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 asborption spectra of the higest redshift quasars. We find that even with conservative estimates for the impact of negative feedback mechanisms, primordial stellar sources contribute significantly to early reionisation. Future observations of a Thomson optical depth of tau_e>~0.13 would bolster the claim for the existence of population III stars similar to the ones studied here.