Gas dynamics in interacting disc galaxies

Behaviour of interstellar gas in a disc galaxy, which is perturbed by another galaxy, is investigated using a scheme of colliding gas clouds in the gravitational potential of N-body stellar models. In the unperturbed state, the parent galaxy has a self-gravitating stellar disc which is stabilized by a halo component. Gas is treated as an ensemble of cloud particles which are distributed in the disc. Their self-gravity is neglected. The perturber is assumed to be a mass point. During a close encounter, a stellar bar is formed in the disc by the tidal force of the perturber as shown in a previous paper of this series. It is found that this stellar bar induces the infall of gas to the nuclear region if the gas dissipates its energy efficiently through cloud-cloud collisions. This mechanism may explain the claimed overabundance of nuclear activities in interacting galaxies. lnfall efficiency depends strongly upon the internal structure of the parent galaxy prior to the encounter such as the distribution of gas and the shape of the rotation curve. The infall is effectively reduced if the inner disc region is gas poor so that the dissipation is inefficient. The bar which is formed in a stellar disc with stronger differential rotation is less effective in driving the gas infall.