Warped polar ring in the Arp 212 galaxy

Abstract

The Fabry-Perot scanning interferometer mounted on the 6-m telescope of the Special Astrophysical Observatory of the Russian Academy of Sciences is used to study the distribution and kinematics of ionized gas in the peculiar galaxy Arp 212 (NGC 7625, IIIZw 102). Two kinematically distinct subsystems—the inner disk and outer emission filaments—are found within the optical radius of the galaxy. The first subsystem, at galactocentric distances r < 3.5 kpc, rotates in the plane of the stellar disk. The inner part of the ionized-gas disk (r<1.5–2 kpc) exactly coincides with the previously known disk consisting of molecular gas. The second subsystem of ionized gas is located at galactocentric distances 2–6 kpc. This subsystem rotates in a plane tilted by a significant angle to the stellar disk. The angle of orbital inclination in the outer disk increases with galactocentric distance and reaches 50° at r ≈ 6 kpc. The ionized fraction of the gaseous disk does not show up beyond this galactocentric distance, but we believe that the HI disk continues to warp and approaches the plane that is polar with respect to the inner disk of the galaxy. Hence Arp 212 can be classified as a galaxy with a polar ring (or a polar disk). The observed kinematics of the ionized and neutral gas can be explained assuming that the distribution of gravitational potential in the galaxy is not spherically symmetric. Most probably, the polar ring have formed via accretion of gas from the dwarf satellite galaxy UGC 12549.