Mergers of elliptical galaxies and dark matter halos: Implications for galaxy assembly

Merging is the fundamental process in the growth of cosmological structures and is central to galaxy formation and evolution. We use numerical simulations to investigate the effects of mergers on dark matter halos and elliptical galaxies and to understand the role of black holes in the merger process.; We first explore mergers of dark matter halos and show that the central properties of a merger remnant are primarily determined by those of its progenitors: mergers of two cuspy halos result in a cuspy remnant, while mergers of two cored halos yield a cored remnant. Halo substructure can have a significant effect on halo structure, however. Massive subhalos sink to the halo center by dynamical friction, heating the halo center, and lose mass due to tidal stripping. The balance between heating and mass deposition determines whether the central density cusp flattens or steepens.; Next, we study major mergers of elliptical galaxies and show that the fundamental plane relation is preserved for all configurations of merger orbits. The projections of the fundamental plane, however, do depend on orbit; this dependence allows us to predict that massive elliptical galaxies, including brightest cluster galaxies, likely formed in dissipationless mergers on relatively radial orbits. The invariance of the fundamental plane is a manifestation of virial equilibrium while the orbital dependence of the projections is due to varying amounts of energy loss from dynamical friction for different orbits.; We also consider minor mergers of ellipticals and the roles dark matter and black holes play in setting the properties of the remnant. Mergers onto a galaxy with a central supermassive black hole generally result in the destruction of the satellite galaxy, preserving the inner structure of the host galaxy. Including dark matter in the galaxies deepens the potential well, increasing the orbital velocities and the amount of tidal heating and stripping of the satellite galaxies. Finally, we investigate how galactic nuclei respond to gravitational radiation recoil, which results from a merger of an unequal-mass black hole binary system. A generic effect of this recoil is to create a core in the galaxy's central density.