Close encounter between galaxies - II. Tidal deformation of a disc galaxy stabilized by massive halo.

A series of disc galaxy models are constructed and their deformation in the tidal interaction is investigated by N-body simulations. Each galaxy model is composed of a self-gravitating disc made up of many particles and a rigid halo component added to stabilize the disc. Each model is characterized by two parameters; the mass fraction of the disc and the mass concentration of the halo toward the centre. It is found that the self-gravitating discs, when perturbed by the tidal force of another galaxy, develop prominent spiral structures not only in the outer region but also in the inner region. This is a remarkable contrast to the case of the massless discs constructed by test particles, in which only the outer part exhibits a spiral structure. Moreover, the spiral structure generally has a bar-like shape in the inner region. Based on these results, the author predicts an overabundance of bars in interacting galaxies.