Different responses to intruder between spirals with live and rigid haloes

We discuss the different dynamical effects of spirals with live and rigid haloes in collisions. Our N-body simulation has 52000 particles. The target is a self-consistent three-dimensional system consisting of a disk and a live halo, the intruder galaxy has a fixed Plummer potential and moves in a straight line through the centre of the target in the plane of the disk. For comparison, the same numerical experiment is made with a rigid halo, all other conditions remaining the same. Differences in the dynamical response and the resulting morphology between the two cases are discussed. It is suggested that the torque on non-axial symmetric spirals exerted by triaxial haloes and the long term effect of dynamical friction of the halo should be further investigated.