IAU Symposium Abstract S186-026T

Collisional Ring Galaxies

P. N. Appleton1
1 Iowa State University, Ames, Iowa, USA pnapplet@iastate.edu

This review will concentrate on a special class of colliding galaxy, the collisional ring galaxies (e. g. The Cartwheel). Ring galaxies are believed to owe their morphology to transient waves formed when a companion of low orbital angular momentum passes through the central regions of a disk galaxy. Collisions between gas-rich systems may have been more common in the past, and the study of nearby ring galaxies may lead to clues about transient star formation processes occurring in collisions seen at high redshift. In particular, models of the penetration of two gas-rich galaxies in a head-on collision lead to predictions of four observationally distinct time-periods in the collision. These are, (1) the initial impact and shock-heating of the disk, (2) ring development and the splattering of rapidly cooling gas into debris plumes, (3) the re-accretion of cool gas onto both galaxies and, (4) the final merger of the companion in low-energy collisions. Recent observations made over a wide range of the electro-magnetic spectrum (including ROSAT, HST and ISO observations) will be reviewed with the aim of constraining, as well as possible, the dynamical history and star formation properties of these galaxies and their companions.