Mittwoch, 7. Oktober 2009 - 15:15
Jorge Moreno (Haverford USA):
"Halo mergers, AGN and downsizing"
Zusammenfassung. We propose a simple analytic model of active galactic nuclei (AGN) triggered by major mergers of dark matter haloes. The model consists of two main ingredients: (1) the halo merger rate as the main triggering agent, and (2) the quasar light curve, which describes the evolution of individual quasars. We use a theoretical merger rate compatible with cosmological simulations, and define major mergers as those with mass ratio of at least 1:3. The light curve has two components: an exponential ascending phase and a power-law descending phase that depends on mass of the host. We postulate a self-regulation condition between the peak luminosity and the mass of the host halo at triggering, and only massive hosts are considered. The descending phase is modelled such that AGN in more massive haloes shut down faster than in less massive ones. This is compatible with downsizing, since observations reveal little or no sign of recent star formation in massive early-type galaxies. Our results match the luminosity function, the quasar clustering, the local black hole mass function, and the Eddington-ratio distribution. We also explore the consequences of extending our model to include minor mergers, less massive hosts and massive black hole seeds. We make predictions for the local M-sigma relation and its redshift evolution. Lastly, we propose a simple evolutionary model where obscured sources only include the first portion of the light curve, while the rest describes optical AGN.