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 AGN self-regulation. However, once having attained a black hole mass of $10^4-10^5\msun$, AGN feedback process can self-regulate to guide the SMBHs to grow at a significantly slower, sub-Eddington rate. By redshift $z\sim 10$ the black hole mass with an initial super-Eddington jump-start is caught up by that in the case with a 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 supermassive black holes of billions of solar masses, our analysis establishes firmer ground for the need of seed masses of $10^4-10^5\msun$ that are not grown via an earlier super-Eddington phase.