On the minimum mass of reionization sources

TL;DR

This paper uses semi-analytical models to determine the minimum mass of star-forming haloes needed for reionization, finding that including minihaloes improves data agreement and that large-galaxies-only models require exotic sources.

Contribution

It introduces calibrated semi-analytical reionization models to estimate the minimum halo mass, highlighting the importance of minihaloes and exotic sources for accurate reionization modeling.

Findings

Halos with M < 10^9 M_sun are insufficient for matching data.

Including minihaloes (~10^6 M_sun) improves model fit.

Large-galaxies-only models need exotic sources at z > 6.

Abstract

By means of carefully calibrated semi-analytical reionization models, we estimate the minimum mass of star-forming haloes required to match the current data. Models which do not include haloes of total mass M < 10^9 M_sun fail at reproducing the Gunn-Peterson and electron scattering optical depths simultaneously, as they contribute too few (many) photons at high (low, z \approx 6) redshift. Marginally acceptable solutions require haloes with M \approx 5 \times 10^7 M_sun at z \approx 10, corresponding to virial temperatures (\sim 10^4K) for which cooling can be ensured by atomic transitions. However, a much better match to the data is obtained if minihaloes (M \sim 10^6 M_sun) are included in the analysis. We have critically examined the assumptions made in our model and conclude that reionization in the large-galaxies-only scenario can remain viable only if metal-free stars and/or some other exotic sources at z > 6 are included.