Conditions for Super-Eddington Accretion onto the First Black Holes

Observations of supermassive 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 efficiency permit. Following our previous 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 × 103 to 6 × 104 M, exploring a range of feedback efficiencies. We also vary the feedback injection radius to probe the threshold of numerical overcooling. 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 × 103−6 × 103 M BH at moderate feedback efficiencies. We discuss the effectiveness of thermal feedback in heating the gas, suppressing accretion, and driving outflows 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.