SCYON Abstract

Received on September 5 2011

Long-term evolution of massive black hole binaries. IV. Mergers of galaxies with collisionally relaxed nuclei

Authors	Alessia Gualandris and David Merritt
Affiliation	Max-Planck Institute for Astrophysics, Garching, Germany Rochester Institute of Technology, Rochester, NY
Submitted to	Astrophysical Journal
Contact	alessiag@mpa-garching.mpg.de
URL	http://arxiv.org/abs/1107.4095
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Abstract

We simulate mergers between galaxies containing collisionally-relaxed nuclei around massive black holes (BHs). Our galaxies contain four mass groups, rep- resentative of old stellar populations; a primary goal is to understand the distri- bution of stellar-mass BHs after the merger. Mergers are followed using direct- summation N-body simulations, assuming a mass ratio of 1:3 and two different orbits. Evolution of the massive BH binary is followed until its separation has shrunk by a factor of 20 below the hard-binary separation. During the galaxy merger, large cores are carved out in the stellar distribution, with radii several times the influence radius of the massive BH. Much of the pre-existing mass segre- gation is erased during this phase. We follow the evolution of the merged galaxies for approximately three, central relaxation times after coalescence of the massive binary; both standard, and top-heavy, mass functions are considered. The cores that were formed in the stellar distribution persist, and the distribution of the stellar-mass black holes evolves against this essentially fixed background. Even after three central relaxation times, these models look very different from the relaxed, multi-mass models that are often assumed to describe the distribution of stars and stellar remnants near a massive BH; in particular, the density of stellar BHs is much smaller than in those models. We discuss the implications of our results for the EMRI problem and for the existence of Bahcall-Wolf cusps.