ABSTRACT

Some of ultra-luminous galaxy mergers show a sign of quasar-like activity. We have numerically investigated the dynamical evolution of the interstellar gas in the late phase of disk galaxy mergers in order to clarify how the gas dynamics is related to the triggering of quasar-like activity. It is found that in most cases the efficient gas infall to the central 10 pc of the nucleus is realized only after the coalescence of two galaxy cores. This suggests that the quasar-like activity tends to appear only after the merger has been completed.

MODELS

The cloud particle scheme has been used to follow the gas response to the time dependent gravitational field made by two galaxy cores spiraling into the mass center of the system. We have neglected the influence of galactic disks because the inner region of a late phase merger is likely to be dynamically dominated by spherical components (e.g., bulges and nuclei). The spherical component (hereafter core) of each galaxy is assumed to be rigid. The self-gravity of the gas has been neglected. The dissipational nature of gas has been included by making gas clouds collide inelastically. Gas clouds are initially distributed in a disk around one of two nuclei.