On the relationship between galaxy formation and quasar evolution

We compare the evolution with cosmic time of the star formation rate per comoving volume in galaxies and of the volume emissivity due to active galactic nuclei, in an attempt to understand the relationship between black hole accretion and the formation of the surrounding structure. We find an interesting similarity between the evolution rates for the total populations of galaxies and AGN, which indicates that, on average, the history of black hole accretion follows that of stellar formation in the host galaxies. Similarly, the evolution of luminous quasars parallels that of the stellar populations in massive spheroidal galaxies, in keeping with the locally established association of supermassive black holes and galactic bulges. We finally comment on our finding that high-luminosity, high-mass systems evolve on a shorter cosmic time-scale than lower mass ones; to explain this, theories of structure formation based on the gravitational collapse of dark matter haloes must be complemented with a detailed description of the dynamical processes in the baryonic component, which dominate the formation and evolution in high-density environments.