Early growth of high redshift black holes

Abstract

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 AGN population remains undetected. In the present 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 \(\rm 3 \times 10^{10}~M_{\odot}\) at \(z=7.5\) and we turn on radiative feedback from a MBH seed of \(\rm 10^5~M_{\odot}\) 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 \(\rm M_{\odot}\) during 320 Myr and the average mass accretion onto the MBH is a few times \(\rm 10^{-6}~M_{\odot}/yr\). 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.