Cosmic reionization after Planck II: contribution from quasars

Understand

In the light of the recent Planck downward revision of the electron scattering optical depth, and of the discovery of a faint AGN population at $z > 4$, we reassess the actual contribution of quasars to cosmic reionization.

• To this aim, we extend our previous MCMC-based data-constrained semi-analytic reionization model and study the role of quasars on global reionization history.
• We find that, the quasars can alone reionize the Universe only for models with very high AGN emissivities at high redshift.
• These models are still allowed by the recent CMB data and most of the observations related to HI reionization.