Hunting a wandering black hole in M31 halo using GPU cluster

In the hierarchical structure formation scenario, galaxies have experienced many mergers with less massive galaxies and have grown larger and larger. On the other hand, the observations indicate that almost all galaxies have a central massive black hole (MBH) whose mass is similar to 10(-3) of its spheroidal component. Consequently, MBHs of satellite galaxies are expected to be moving in the halo of their host galaxy after a galaxy collision, although we have not found such MBHs yet. We investigate the current-plausible position of an MBH of the infalling galaxy in the halo of the Andromeda galaxy (M31). Many substructures are found in the M31 halo, and some of them are shown to be remnants of a minor merger about 1 Gyr ago based on theoretical studies using N-body simulations. We calculate possible orbits of the MBH within the progenitor dwarf galaxy using N-body simulations. Our results show that the MBH is within the halo, about 30 kpc away from the center of M31. In addition, further simulations are necessary to restrict the area in which the MBH exists, and hence to determine the observational field for the future observational detection. The most uncertainty of the current MBH position is caused by uncertainty about the infalling orbit of the progenitor dwarf galaxy. Therefore, we have performed a large (a few 10(4) realizations) set of parameter study to constrain the orbit in the six-dimensional phase space. For such purpose, we have already investigated in detail a few ten thousand orbit models using HA-PACS, a recently installed GPU cluster in University of Tsukuba.