Early growth of typical high-redshift black holes seeded by direct collapse

Understanding the growth of high-redshift massive black holes (MBHs) is a problem of great astrophysical interest. The most luminous quasars at z > 6 are frequently observed but they represent only the tip of the iceberg as the majority of the low-luminosity active galactic nuclei (AGN) population remains undetected. In this study, we perform a radiation hydrodynamics cosmological simulation to study the growth of 'normal' black holes in the high-redshift universe. In our simulation, we model the formation of Pop III and Pop II stars along with their chemical, mechanical, and radiative feedback.We consider both UV and X-ray emission from an accreting BH to simulate its radiative feedback. The selected halo has a mass of 3 × 10¹⁰M_⊙ at z = 7.5 and we turn on radiative feedback from a MBH seed of 10⁵M_⊙ along with in situ star formation at z = 12 when the halo mass reaches well above the atomic cooling limit. We find that the MBH accretes only about 2200 M_⊙ during 320 Myr and the average mass accretion on to the MBH is a few times 10^-6M_⊙ yr^-1. Our results suggest that the stunted growth of MBH is a consequence of supernovae in tandem with MBH feedback which drive large outflows and evacuate the gas from MBH vicinity. This may explain why a population of low-luminosity AGN has not been detected so-far at z > 6; the large contrast between the star formation rate and the MBH accretion rate may make then hard to detect even in upcoming deep surveys.