The origin of most massive black holes at high-z: BLUETIDES and the next quasar frontier

TL;DR

This study uses the BlueTides cosmological simulation to investigate the early growth of supermassive black holes at high redshift, revealing the importance of tidal fields and gas accretion modes in their rapid formation.

Contribution

It demonstrates how large-scale hydrodynamical simulations can identify the environmental conditions that enable the fastest early black hole growth, emphasizing the role of tidal fields over mergers.

Findings

Most massive black holes at z=8 reach ~4 x 10^8 Msun.

Low tidal fields facilitate cold gas accretion and compact galaxy formation.

Mergers are minor in the initial growth of early supermassive black holes.

Abstract

The growth of the most massive black holes in the early universe, consistent with the detection of highly luminous quasars at $z> 6$ implies sustained, critical accretion of material to grow and power them. Given a black hole seed scenario, it is still uncertain which conditions in the early Universe allow the fastest black hole growth. Large scale hydrodynamical cosmological simulations of structure formation allow us to explore the conditions conducive to the growth of the earliest supermassive black holes. We use the cosmological hydrodynamic simulation BlueTides, which incorporates a variety of baryon physics in a (400 Mpc/h)^3 volume with 0.7 trillion particles to follow the earliest phases of black hole critical growth. At z=8 the most massive black holes (a handful) approach masses of 10^8 Msun with the most massive (with M_BH = 4 x 10^8 Msun ) being found in an extremely compact spheroid-dominated host galaxy. Examining the large-scale environment of hosts, we find that the initial tidal field is more important than overdensity in setting the conditions for early BH growth. In regions of low tidal fields gas accretes 'cold' onto the black hole and falls along thin, radial filaments straight into the center forming the most compact galaxies and most massive black holes at earliest times. Regions of high tidal fields instead induce larger coherent angular momenta and influence the formation of the first population of massive compact disks. The extreme early growth depends on the early interplay of high gas densities and the tidal field that shapes the mode of accretion. Mergers play a minor role in the formation of the first generation, rare massive BHs.