Formation of a Polar Ring Galaxy in a Galaxy Merger

Abstract

We numerically investigate stellar and gas dynamics in star-forming and dissipative galaxy mergers between two disk galaxies with speciÐc orbital conÐgurations. We Ðnd that violent relaxation combined with gaseous dissipation in galaxy merging transforms two disk galaxies into one S0 galaxy with polar rings ; both the central S0-like host and the polar ring component in a polar ring galaxy are originally disk galaxies. We also Ðnd that morphology of the developed polar rings reÑects both the initial orbit conÐguration of galaxy merging and the initial mass ratio of the two merger progenitor disk galaxies. Based upon these results, we discuss the origin of the fundamental observational properties of polar ring galaxies, such as the prevalence of S0 galaxies among polar ring galaxies, the rarity of polar ring galaxies among S0 galaxies, the dichotomy between narrow polar rings and annular ones, the shapes of polar ring warps, and an appreciably larger amount of interstellar gas in the polar ring component.