Conditions for super-Eddington accretion onto the first black holes

Abstract

Observ ations of supermassi ve black holes (BHs) at high redshift challenge our understanding of the evolution of the first generation of BHs in proto-galactic environments. One possibility is that they grow much more rapidly than current estimates of feedback and accretion efficienc y permit. F ollo wing our pre vious analysis of super-Eddington accretion on to stellar- mass BHs in mini-haloes under no-feedback conditions, we now investigate whether this can be sustained when thermal feedback is included. We use four sets of cosmological simulations at sub-pc resolution with initial BH masses varying from 1 ×10 3 to 6 ×10 4 M⊙, exploring a range of feedback efficiencies. We also vary the feedback injection radius to probe the threshold of numerical o v ercooling. We find that super-Eddington growth sustained of the order of ∼100 kyr is possible with weak thermal feedback efficiency in all environments and moderate efficiency for two of the BHs. Trans-Eddington growth is possible for a 3 ×10 3 -6 ×10 3 M⊙ BH at moderate feedback efficiencies. We discuss the effectiveness of thermal feedback in heating the gas, suppressing accretion, and dri ving outflo ws at these parameter configurations. Our results suggest that super-Eddington growth may be possible in the presence of thermal feedback for BHs formed from the first stars.