Modelling the merging history of Binary SMBHs in Hierarchical Models of Galaxy Formation

We present a model describing the evolution of a Super Massive Black Holes (SMBHs) population within the framework of hierarchical models of galaxy formation. The occurrence of SMBHs binaries at different redshifts and the influence of the interacting SMBHS on the host galaxies are studied by means of Montecarlo realizations of halo merging histories, coupled with a semi-analytical treatment of the interactions between the systems. We find that the main parameters governing the coalescence timescale, and hence the fraction of binary systems, are the initial mass and the accretion history of the SMBHs. This revised version was published online in September 2006 with corrections to the Cover Date.