  The mass density of massive black holes observed locally is consistent with
the hard X-ray Background provided that most of the radiation produced during
their growth was absorbed by surrounding gas. A simple model is proposed here
for the formation of galaxy bulges and central black holes in which young
spheroidal galaxies have a significant distributed component of cold dusty
clouds which accounts for the absorption. The central accreting black hole is
assumed to emit both a quasar-like spectrum, which is absorbed by the
surrounding gas, and a slow wind. The power in both is less than the Eddington
limit for the black hole. The wind however exerts the most force on the gas
and, as earlier suggested by Silk & Rees, when the black hole reaches a
critical mass, it is powerful enough to eject the cold gas from the galaxy, so
terminating the growth of both black hole and galaxy. In the present model this
point occurs when the Thomson depth in the surrounding gas has dropped to about
unity and results in the mass of the black hole being proportional to the mass
of the spheroid, with the normalization agreeing with that found for local
galaxies by Magorrian et al. for reasonable wind parameters. The model predicts
a new population of hard X-ray and sub-mm sources at redshifts above one which
are powered by black holes in their main growth phase.
