Dark-ages reionization and galaxy formation simulation -- XVIII. The high-redshift evolution of black holes and their host galaxies

TL;DR

This study uses the Meraxes semi-analytic model to analyze the evolution of black holes and their host galaxies from high redshift to today, revealing stable black hole-host relations and growth driven mainly by secular processes.

Contribution

It provides new insights into black hole and galaxy co-evolution, showing no significant evolution in key relations up to redshift 8 and emphasizing secular growth mechanisms.

Findings

Black hole-bulge and black hole-total stellar mass relations show little evolution up to redshift 8.

Growth of black holes and galaxies is tightly correlated even at high redshifts.

Secular processes dominate black hole growth over mergers at all redshifts.

Abstract

Correlations between black holes and their host galaxies provide insight into what drives black hole-host co-evolution. We use the Meraxes semi-analytic model to investigate the growth of black holes and their host galaxies from high redshift to the present day. Our modelling finds no significant evolution in the black hole-bulge and black hole-total stellar mass relations out to a redshift of 8. The black hole-total stellar mass relation has similar but slightly larger scatter than the black hole-bulge relation, with the scatter in both decreasing with increasing redshift. In our modelling the growth of galaxies, bulges and black holes are all tightly related, even at the highest redshifts. We find that black hole growth is dominated by instability-driven or secular quasar-mode growth and not by merger-driven growth at all redshifts. Our model also predicts that disc-dominated galaxies lie on the black hole-total stellar mass relation, but lie offset from the black hole-bulge mass relation, in agreement with recent observations and hydrodynamical simulations.