The limited role of mergers in the black hole to bulge mass relation
  We examine the intrinsic scatter in the correlation between black hole masses
and their host bulge masses, and find that it cannot be accounted for by
mergers alone. A simple merger scenario of small galaxies leads to a
proportionality relation between the late-time black hole and bulge masses,
with intrinsic scatter (in linear scale) increasing along the ridge line of the
relation as the square root of the mass. By examining a sample of 86 galaxies
with well measured black hole masses, we find that the intrinsic scatter
increases with mass more rapidly than expected from the merger-only scenario.
We discuss the possibility that the feedback mechanism that operated during
galaxy formation involved the presence of a cooling flow.
