X iv : a st ro - p h / 97 04 10 4 v 1 1 1 A pr 1 99 7 H II Region Abundances in the Polar Ring of NGC 2685 1 Paul

We have obtained optical spectrophotometry of 11 H II regions in the polar ring of NGC 2685 (the Helix galaxy), and have used these data to study the physical characteristics of the polar-ring H II regions. The H II regions have normal spectra with no suggestion of unusual density, temperature, extinction, or composition. Semi-empirical calculations yield high oxygen abundance estimates (0.8–1.1 Z⊙) in all H II regions. This, along with the observed (B−V ) color, Hα equivalent width, and molecular gas properties argue against the current picture in which polar rings form from tidally captured dwarf irregular galaxies, and suggests instead that the rings are long-lived, self-gravitating structures as predicted by some dynamical models. This would allow the time required for multiple generations of star formation, and for the retention of the resulting enriched ejecta for inclusion in further generations of star formation. Subject headings: galaxies: abundances — galaxies: individual (NGC 2685) — galaxies: interactions — ISM: H II regions This paper is partially based on observations obtained with the Multiple Mirror Telescope, a joint facility of the Smithsonian Institution and the University of Arizona. [email protected] [email protected]