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