Speaker
Dr
Andrea Merloni
(MPE)
Description
How did supermassive black holes form and grow in the nuclei of galaxies? Why are their physical properties today so tightly linked to those of their hosts? What was the impact on the surrounding structures of the copious energy release, either in radiative or mechanical form, associated to the growth of such black holes in active galactic nuclei (AGN)? I will show how constraints available from a study of AGN evolution on the growth of the supermassive black holes can be used to give at least partial answers to some of these questions.
I will first discuss constraints on the average radiative efficiency of rapidly growing black holes based on the observed evolution of the AGN luminosity function. An outlook on their kinetic luminosity function evolution will also be discussed, thus providing a robust physical framework for phenomenological models of AGN feedback within structure formation.
Finally, using the rich multi-band photometry in the COSMOS field I will present
the host galaxy properties of a large, complete, sample of X-ray and spectroscopically selected AGN. The probability for a galaxy to host a black hole growing at any given specific accretion rate (the ratio of X-ray
luminosity to the host stellar mass) is independent of the galaxy mass and follows a power-law distribution in specific accretion rate. By looking at the normalization
of such a probability distribution, we show how the incidence of AGN
increases with redshift as rapidly as (1+z)^4, in close
resemblance with the overall evolution of the specific star formation rate.
Although AGN activity and star formation appear to have a common triggering mechanism, we do not find any 'smoking gun' signaling powerful AGN influence on the global properties of their host galaxies.
Author
Dr
Andrea Merloni
(MPE)