Talk Title: Reconstructing the Dynamics of Super Massive Black Holes During the Assembly of Galaxies and Galaxy Halos: The View from state-of-the-art N-body/SPH Simulations
Abstract: We present the results of a large set of new N-body/SPH simulations of binary mergers of disk galaxies with mass ratios of 1:1, 2:1, 3:1, and 4:1, using unprecedented resolution. The multi-component galaxy models we adopt comprise a stellar and a gaseous disk, a bulge, and an extended dark matter halo; their structure is based on the currently favored galaxy formation paradigm within cold dark matter models. At the center of each galaxy, a super-massive black hole is also included, whose mass obeys the $M_{\rm BH}-\sigma$ relation between the black hole mass and the velocity dispersion of the host bulge. The orbital configurations of the encounters are chosen according to recent results of high-resolution cosmological simulations and mimic mergers that occur both at high and low redshift. Tidal and hydrodynamical torques acting during the mergers drive considerable amounts of gas toward the center of the galaxies. However, while in the adiabatic runs, shock heating dominates in the final stage and leads to a fairly extended gas distribution in the remnants, in the simulations where radiative cooling is incorporated gas dissipates efficiently and often settles into a rotationally supported disk-like structure. We find that radiative cooling leads to baryonic dominance in the central few kpc of the remnants and that the very massive nuclear disks that form might fuel the central black holes by losing angular momentum through gravitational instability mechanisms. We discuss the implications of our results for crucial issues including the efficiency of the super-massive black hole binary formation following a galaxy merger, the dependence of the pairing process on the internal structure of the galaxies, and the origin and evolution of the $M_{\rm BH}-\sigma$ relation.
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