Formation of Polar Ring S0 Galaxies in Dissipative Galaxy Mergers

We numerically investigate stellar and gasdynamics of galaxy mergers between gas-rich, late-type spirals in order to explore the origin of polar ring S0 galaxies. We found that dissipative galaxy merging with a particular orbit configuration transforms two late-type spirals into one S0 galaxy with polar rings. The formation process of polar ring S0 galaxies is described as follows. A spiral galaxy intruding from the polar axis of the other victim galaxy excites the outwardly propagating density wave in the gaseous component of the victim galaxy. The subsequent gaseous dissipation and star formation dramatically transform the victim galaxy into polar rings. The intruding galaxy, on the other hand, is inevitably transformed into a rapidly rotating and spindly S0 galaxy, owing to the violent gravitational interaction of galaxy merging. This numerical result implies that dissipative galaxy merging between two gas-rich spirals is a new, promising candidate that can explain not only the formation of the central S0-like host but also the formation of a gas-rich polar ring component in a polar ring S0 galaxy.