Merging between a central massive black hole and a compact stellar system: A clue to the origin of M31’s nucleus

The central bulge of M31 is observed to have two distinct brightness peaks with the separation of ∼ 2 pc. Tremaine (1995) recently proposed a new idea that the M31’s nucleus is actually a single thick eccentric disk surrounding the central super-massive black hole. In order to explore the origin of the proposed eccentric disk, we numerically investigate the dynamical evolution of a merger between a central massive black hole with the mass of ∼ 10 M⊙ and a compact stellar system with the mass of ∼ 10 M⊙ and the size of a few pc in the central 10 pc of a galactic bulge. We found that the stellar system is destroyed by strong tidal field of the massive black hole and consequently forms a rotating nuclear thick stellar disk. The orbit of each stellar component in the developed disk is rather eccentric with the mean eccentricity of ∼ 0.5. These results imply that the M31’s nuclear eccentric disk proposed by Tremaine (1995) can be formed by merging between a central massive black hole and a compact stellar system. We furthermore discuss when and how a compact stellar system is transferred into the nuclear region around a massive black hole. Subject headings: galaxies: individual (M31) – galaxies: nuclei – galaxies: elliptical and lenticular, cD – galaxies: kinematics and dynamics – galaxies: interaction