On the contribution of (mini)quasars to reionization

Recent data from WMAP and SDSS implies that the reionization history of the universe is extended and complex. These discoveries motivated models in which the ionizing radiation from accreting black holes, residing in shallow dark matter potential wells, dominate the ionization of the universe at redshifts z = 10–20. Here we show that (1) contrary to previous beliefs, photoionization heating does not prevent gas from cooling and condensing in small (vcirc ∼ 10 km/s) dark matter potential wells at z ≳ 10; but (2) current models in which an early generation of accreting small black holes dominate full reionization, saturate the unresolved soft X-ray background at the ≳2σ level.