Supermassive black holes and AGNs in hierarchical galaxy formation

We include the accretion of gas onto supermassive black holes (BHs) into a semi-analytic model of galaxy formation in the cosmological framework of hierarchical clustering. The feeding of BHs is triggered by the galaxy interactions, while the gas available for supply is computed self-consistently in the model. In such a cosmological framework the Eddington ratio lambda for AGNs is predicted to follow a bimodal distribution at z <= 2, with high-lambda branch corresponding to bright AGNs (with luminosities L > 10(45) ergs s(-1)) and with a growing population in the low-A branch contributed by faint AGNs (with luminosities L < 10(44) ergs s(-1)). At higher redshift the distribution is instead peaked at high values of lambda = 0.3 - 1.