The Formation of the First Quasars. I. The Black Hole Seeds, Accretion and Feedback Models
Abstract
Supermassive black holes (SMBHs) of 109\, M are generally believed to be the central engines of the luminous quasars observed at z6, but their astrophysical origin remains elusive. The z quasars reside in rare density peaks, which poses several challenges to uniform hydrodynamic simulations. To investigate the formation of these distant quasars, we perform a suite of zoom-in simulations on a favorable halo, with a mass of 1013\, M at z = 6 and a history of multiple major mergers, ideal for BH growth. We test BH seeds of 10 - 106\, M, and various accretion and feedback models, including thin-disk and slim-disk accretion. We find, contrary to previous studies, that light seeds of 103\, M fail to grow to 108\, M by z 6 even with super-critical accretion; that the hyper-Eddington mode leads to lower accretion rates than the Eddington-limited case due to stronger feedback, resulting in significantly smaller BHs by two orders of magnitude; and that while the super-critical model boosts the growth of low-spin BHs, for high-spin BHs the mass may be reduced due to increased radiative feedback. Our simulations show that the first 108 - 109\, M SMBHs may grow from heavy seeds of 104\, M via Eddington-limited or mild super-critical accretion facilitated by gas-rich mergers and self-regulated by feedback, and they co-evolve with their host galaxies, producing bright quasars such as those at z6 and ULAS J1342+0928, currently the most distant quasar at z = 7.54.