The mini-QSO's contribution to cosmic reionization

By employing an improved simulation of the evolution of black holes (BHs) based on the merger tree of dark matter halos, we explore the relationship between the central BH mass M bh and velocity dispersion σ * at high redshift z ≥ 6 and quantify the mini-QSO's (with BH mass M = 200 - 105 M ⊙ ) contribution to cosmic reionization. The simulation demonstrates how seed BHs migrate onto the M BH -σ * relation by merging with each other and accreting gas at z ≥ 6: 1. The correlation between BHs and their host halos increases as the BHs grow; 2. The slope, i.e. Φ = d log( M bh )/d log(σ * ) in the relationship, is insensitive to the redshift at z > 6. In agreement with previous work, we find that mini-QSOs' ionizing capability to the Universe lies in the range ~ 25% - 50% if early miniquasars have extremely high duty cycles, i.e. P ( z > 6) ~ 0.9 - 1.