Towards an understanding of the evolution of the scaling relations for
  supermassive black holes
  The growth of the supermassive black holes (BHs) that reside at the centres
of most galaxies is intertwined with the physical processes that drive the
formation of the galaxies themselves. The evolution of the relations between
the mass of the BH, m_BH, and the properties of its host therefore represent
crucial aspects of the galaxy formation process. We use a cosmological
simulation, as well as an analytical model, to investigate how and why the
scaling relations for BHs evolve with cosmic time. We find that a simulation
that reproduces the observed redshift zero relations between m_BH and the
properties of its host galaxy, as well as the thermodynamic profiles of the
intragroup medium, also reproduces the observed evolution in the ratio m_BH/m_s
for massive galaxies, although the evolution of the m_BH/sigma relation is in
apparent conflict with observations. The simulation predicts that the relations
between m_BH and the binding energies of both the galaxy and its dark matter
halo do not evolve, while the ratio m_BH/m_halo increases with redshift. The
simple, analytic model of Booth & Schaye (2010), in which the mass of the BH is
controlled by the gravitational binding energy of its host halo, quantitatively
reproduces the latter two results. Finally, we can explain the evolution in the
relations between m_BH and the mass and binding energy of the stellar component
of its host galaxy for massive galaxies (m_s~10^11 M_sun) at low redshift (z<1)
if these galaxies grow primarily through dry mergers.
