Gas fueling and nuclear disk formation in merging between a central black hole and a gas clump

Abstract

We numerically investigate dynamical evolution of a merger between a central massive black hole (MBH) and a gas clump with the mass of $10^6$ $-$ $10^7$ $M_{\odot}$ in the central tens pc of a galactic bulge. We found that strong tidal gravitational field of the MBH transforms the initial spherical clump into a moderately thick gaseous disk (or torus) around the MBH. The developed disk is also found to show rotation, essentially because the tidal field changes efficiently the orbital angular momentum of the clump into intrinsic angular momentum of the disk. Furthermore about a few percent of gas mass (corresponding to a few $10^5$ $M_{\odot}$) in the clump is found to be transferred to the central sub-parsec region around the MBH within an order of $10^6$ yr. We thus suggest that successive merging of gas clumps onto a MBH can not only be associated closely with the formation of nuclear disk around the MBH but also can provide gas fuel for the MBH.