Published in Fundamentals of Cosmic Physics, Vol. 16, pp. 111-220, 1996.

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COLLISIONAL RING GALAXIES

P.N. Appleton and Curtis Struck-Marcell

Erwin W. Fick Observatory and Department of Physics and Astronomy, Iowa State University, Ames, IA 50011

Abstract. We review the current state of knowledge of both the observational and theoretical nature of collisional ring galaxies. Ring galaxies represent a class of colliding galaxy in which nearly symmetrical density waves are driven into a disk as a result of an almost bulls-eye collision with another galaxy. Since the basic dynamics of the collision is now quite well understood, the ring galaxies can be used as a form of cosmic perturbation "experiment" to explore various properties of galactic disks. For example, as the density wave expands into the disk, it triggers the birth of large numbers of massive stars. This provides us with an opportunity to study the evolution of stars and star clusters in the wake of the ring. We review the now extensive observations of ring galaxies from the early photographic measurements to recent infrared, radio and optical studies. We also present a simple analytical treatment of the ring-making collisions and compare them to recent N-body and gas-dynamical models. The importance of ring galaxies lies in their relative simplicity compared with other colliding systems and the possibility that low-angular momentum collisions might have been more common in the past.

Keywords: Interacting galaxies, Colliding galaxies, Star formation in galaxies, Ring galaxies, Dynamics of interacting systems, Starburst activity in galaxies

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