  The shining of quasars is a likely trigger of massive galatic winds, able to
remove most ISM from a star-forming spheroid. However, the mechanism
responsible for the deposition of energy into the ISM is still unclear.
Starting from a model for feedback in galaxy formation with a two-phase medium
(Monaco 2004a), we propose that the perturbation induced by radiative heating
from a quasar on the ISM triggers a critical change of feedback regime. In the
feedback model, SNRs expanding in the hot and pressurized phase of a
star-forming spheroid tipically become pressure-confined before the hot
interior gas is able to cool. Whenever the evaporation flow due to radiative
heating of the quasar is significant with respect to the star-formation rate,
the SNRs reach the point where their interior gas cools before being confined,
forming a thick cold shell. We show that in this conditions the shells
percolate into a super-shell of cold gas that sweeps the whole galaxy.
Radiation pressure then pushes the shell out of the galaxy. This self-limiting
mechanism leads to a correlation between black hole and bulge masses. The
insertion of a motivated wind trigger criterion in a hierarchical galaxy
formation model shows however that winds are not necessary to obtain a good
black hole--bulge correlation. In absence of winds, good results are obtained
if the mechanism responsible for the creation of a reservoir of low-angular
momentum gas (able to accrete onto the black hole) deposits mass at a rate
proportional to the star-formation rate. Using a novel galaxy formation model,
we show under which conditions black hole masses are self-limited by the wind
mechanism described above, and outline the possible observational consequences
of this self-limitation. [Abridged]
