Origin of the anti-hierarchical growth of black holes

Understand

Observational studies have revealed a "downsizing" trend in black hole (BH) growth: the number densities of luminous AGN peak at higher redshifts than those of faint AGN.

• This would seem to imply that massive black holes formed before low mass black holes, in apparent contradiction to hierarchical clustering scenarios.
• We investigate whether this observed "downsizing" in BH growth is reproduced in a semi-analytic model for the formation and evolution of galaxies and black holes, set within the hierarchical paradigm for structure formation (Somerville et al.
• 2008; S08).