Joining the Dots: High Redshift Black holes

TL;DR

This paper supports a model where high-redshift supermassive black holes are highly collimated and embedded in thick, obscuring environments, explaining their faint X-ray signals and rapid early growth consistent with observations.

Contribution

It demonstrates that super-Eddington accretion and collimation can explain the observed properties of high-redshift black holes, aligning theory with recent data.

Findings

High-redshift black holes should be X-ray faint and Compton thick.

Black hole growth at high redshift involves super-Eddington accretion rates.

Theoretical predictions match observed black hole to galaxy mass ratios at high redshift.

Abstract

A recent paper (King, 2024) suggested that emission from the central supermassive black holes in high-redshift galaxies must be tightly collimated by the effects of partly expelling a super-Eddington mass supply. I show here that this idea predicts that these galaxies should produce very little detectable rest-frame X-ray emission, appear Compton thick, and show no easily detectable sign of outflows. All of these properties agree with current observations. To produce these effects, the mass supply to the black holes should exceed the Eddington rate by factors 50 - 100, which appears in line with conditions during the early growth of the holes. I note that theoretical derivations of the ratio of black hole mass to host galaxy stellar mass already predict that this should increase significantly at high redshift, in line with recent observations.