Constraining the epoch of reionization

The only acceptable solutions are concentrated in two narrow sets. In one of them reionization proceeds in two phases: a first one driven by Population III stars, completed at z~10, and after a short recombination period a second one driven by normal galaxies, completed at z~6.

In the other set both kinds of sources work in parallel until full reionization at z~6. The best solution with double reionization gives excellent fits to all the observed cosmic histories, but the CMB optical depth is 3{sigma} larger than the recent estimate from the Planck data. Alternatively, the best solution with single reionization gives less good fits to the observed star formation rate density and cold gas mass density histories, but the CMB optical depth is consistent with that estimate.