A close look to quasar-triggered winds: is the black hole-bulge relation self-regulated?

Abstract

We discuss the role of feedback from AGNs on the formation of spheroidal galaxies. The energy released by an accreting Black Hole (BH) may be injected into the ISM through blast waves arising directly from the central engine, radiation pressure or radiative heating. A scenario is described in which radiative heating perturbs the methabolism of a star-forming spheroid, leading to a critical stage where SNe form a cold expanding shell, pushed out of the galaxy by radiation pressure from the AGN. This mechanism can regulate the BH--bulge relation to the observed value. However, this relation may be simply imprinted by the mechanism responsible for the nearly complete loss of angular momentum of the gas that accretes onto the BH. Using a novel model of galaxy formation that includes AGNs, we show that models without self-regulation have problems in reproducing the correct slope of the AGN luminosity function, while models with winds give a much better fit; however, all these models are almost indistingishable as far as their predicted BH--bulge relation is concerned. Finally, we show that the downsizing of the faint AGNs is most likely due to kinetic feedback in star-forming bulges.