Starbursts in multiple galaxy mergers

Abstract

We numerically investigate stellar and gaseous dynamical evolution of mergers between five identical late-type disk galaxies with the special emphasis on star formation history and chemical evolution of multiple galaxy mergers. We found that multiple encounter and merging can trigger repetitive massive starbursts (typically $\sim$ 100 $M_{\odot}$ ${\rm yr}^{-1}$) owing to the strong tidal disturbance and the resultant gaseous dissipation during merging. The magnitude of the starburst is found to depend on initial virial ratio (i.e., the ratio of total kinematical energy to total potential energy) such that the maximum star formation rate is larger for the merger with smaller virial ratio. Furthermore we found that the time interval between the epochs of the triggered starbursts is longer for the merger with the larger virial ratio. The remnant of a multiple galaxy merger with massive starbursts is found to have metal-poor gaseous halo that is formed by tidal stripping during the merging. We accordingly suggest that metal-poor gaseous halo in a field elliptical galaxy is a fossil record of the past multiple merging events for the galaxy.