Abstract
This lecture focuses on the close relationship between bulge masses and black hole masses, and hence on black hole demography. This relationship is very well verified for high masses, but is more dispersed at low masses. Likewise, barred galaxies are an exception, perhaps because the bulbs in barred galaxies are only pseudo-bulbs, or because the kinematics in a barred galaxy are not circular, but elongated. Interacting galaxies are also exceptions (mergers in progress). Recently, black holes too massive for the relationship have been observed at high redshift, early in the Universe. Could it be that black holes grow in mass faster than bulbs, and then catch up? This hypothesis seems to be supported by the fact that overly-massive black holes are also observed in galaxy clusters, at least for cluster-centered galaxies. These are prevented from forming stars, as the intracluster gas is heated to temperatures in excess of a million degrees by the interactions. The formation of bulges is therefore prevented, and cannot catch up with that of black holes. The relationship between masses is interpreted as a feedback effect of AGNs on star formation. Even if the central AGN has little volume of action on the galaxy, its energy is more than enough to destroy the entire galaxy. The problem is then the coupling between the AGN's energy and the galaxy's matter. If the matter is ejected perpendicular to the plane of the galaxy, there won't be much coupling. In many cases, however, the accretion disk does not have the same inclination as the galactic disk, and the matter ejected by the AGN can collide with the galaxy and moderate star formation. Quasars may be the final stage in a merger between two spiral galaxies.
