Constraining the quasar contribution to the reionization of cosmic hydrogen

Abstract

Absorption spectra of high-redshift quasars suggest that the reionization of cosmic hydrogen was complete near z ∼ 6. The dominant sources of ionizing photons responsible for this reionization are generally thought to be stars and quasars. In this paper we make a quantitative estimate of the relative contributions made by these sources. Our approach is to compute the evolution of the post-overlap ionizing background radiation by combining semi-analytic descriptions of reionization in a clumpy medium with a model for the quasar luminosity function. Our overall model has two free parameters, the star formation efficiency and the minimum quasar luminosity. By adjusting these parameters, we cons..