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abstract
Observed ring galaxies fall into several types, some rings are polar whereas others lie in the disk plane of the galaxy. Of the latter type, those that are designated P by Few and Madore (1986) or RING by de Vaucouleurs et al (1976) typically have a close companion of somewhat comparable size (within a factor of five, say) and show a knotty structure of star formation within a full or partial ring. These galaxies have elevated far IR emission and blue spectral colors which, together with bright HII regions, suggests considerable recent star formation. Detailed spectroscopic investigations of the strings of knots around the partial rings have indicated a time sequencing of the star formation from knot to knot. As such these galaxies are ideal laboratories for the study of the star formation resulting from the passage of a density wave through a gaseous disk. The simple geometry and restriction of the star formation to the ring structure allow for a detailed comparison between observations and detailed models of the dynamics of the gas and stars following a galaxy collision. In this paper we present the results of a study in which we have produced combined N-body/Smooth Particle Hydrodynamics, three dimensional simulations of collisions of comparable mass elliptical and disk galaxies, with a variety of impact parameters, but all relative trajectories parallel to the rotation axis of the disk galaxy. With this data set we are able to identify a major subclassifications of P ring galaxies with differences in impact parameter and to explore some of the other unusual features of these galaxies, such as apparently missing nuclei, in terms of the detailed dynamics of both the stars and gas.
