Abstract
We study the formation and evolution of rings in disk galaxies by the impact of a spherical companion. This study is carried out by using numerical simulations and fully self-consistent models. We have tested a number of target disk galaxies with different radial scalelengths or central radial velocity dispersion, and a number of companions with different masses and radial scalelengths. We also have tested a large number of initial conditions to produce collisions with different velocities, inclinations and impact parameters. Our main results are: (a) strong interactions (high companion mass and/or slow impact velocity) result in rings with constant expansion velocity; (b) our tested collisions are very effective to heat the disk, increasing the radial velocity dispersion; (c) the rings created by collisions are certainly density waves; (d) inclined-central collisions create inclined rings, but they are not effective to displace the nucleus of the target; (e) perpendicular-peripheral collisions are more effective to displace the nucleus, as well as to create inclined rings, which remain inclined for a long period of time (some 10^8 years).
