Talk Title: BH accretion and of Starbursts Triggered by Interactions in Hierarchical Galaxy Formation
Abstract: We present the results of a semi-analytic model of galaxy formation which includes a physical description of the starbursts and of accretion onto the central massive BHs. Both such processes are connected to the amount of galactic cold gas destabilized during galaxy encounters. As a result, at high $z$ the protogalaxies grow rapidly by hierarchical merging; meanwhile, much fresh gas is imported and destabilized, so the holes are fueled at their full Eddington rates, and the starbursts are effective to build up a large fraction of the star content of massive galaxies. At lower $z$ the merging rate decline, the refueling peters out, as the residual gas is exhausted while the destabilizing encounters dwindle. So our model uniquely produces at $z>3$ a rise, and at $z\lesssim 2.5$ a decline of the bright QSO population as steep as observed; the predicted local $m_{BH}-\sigma$ relation and the luminosity functions of QSOs from $z\approx 5$ to $z\approx 0$ fit the observations. The corresponding history of starbursts is such that the high-$z$ star formation rate, the B-band luminosity functions, and the luminosity and $z$-distribution of galaxies in K-band at $z\lesssim 2$, all match the existing observations concerning the bright galaxy population.
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