ABSTRACT

We present numerical N-body simulations of galactic interactions in which a compact body or galaxy penetrates a disklike galaxy. The results are ringlike structures having morphologies in good agreement with what one observes as ring galaxies. The code used is the TREE-code by L. Hernquist.

NUMERICAL FEATURES

The disk used as target is imbedded in a massive halo and the whole system is in dynamical equilibrium. It models fairly well the kinematical behaviour of spiral galaxies as far as the velocity distribution is concerned. We performed numerical simulations of collisions between stellar disks (embedded in static halos) and suitable intruders.

The disks have been settled down by solving numerically the Laplace equation in cylindrical coordinates and then immersed in a massive halo structure (King model). The system is evolved several rotation periods to test out the stability. The halo has an important heating effect on the disk during the assessment.

The companions used as intruders are massive points or small king spheres, having different masses and different radii. A series of collisions have been performed varying the direction of the companion's velocity.

The time scale of evolution of the system is around 0.5 Gyr and is consistent with theory (Theys and Spiegel 1977)

EVOLUTION OF THE SYSTEM

The passage of the massive point through the disk generates a transient ringshaped mass distribution. The ring is produced by a single density wave propagating through the disk. The wave has a damped oscillatory behaviour, since after an initial outward propagation, goes backward with decreasing amplitude toward the center of the structure. Correspondingly to the inward propagation, the ring disappears.