How Fast Could Supermassive Black Holes Grow at the Epoch of Reionization?

Abstract Utilizing cosmological hydrodynamic simulations, we show that there is a brief super-Eddington accretion phase in typical halos at high redshift, impervious to active galactic nucleus (AGN) self-regulation. However, once having attained a black hole mass of 10 4 –10 5 M ⊙ , the AGN feedback process can self-regulate to guide the supermassive black holes (SMBHs) to grow at a significantly slower, sub-Eddington rate. By redshift z ∼ 10 the black hole mass with an initial super-Eddington jump-start is caught up by that of the steady Eddington-limited case. Thus, a continuous Eddington limit case represents the fastest possible route to maximally grow SMBHs. To account for the observed z = 7–10 quasars with SMHBs of billions of solar masses, our analysis establishes firmer ground for the need for seed masses of 10 4 –10 5 M ⊙ that are not grown via an earlier super-Eddington phase.