A Spectroscopic and Photometric Study of NGC 2685, the Prototype Polar-Ring Galaxy

Abstract

We present and analyze spectroscopic and photometric observations for NGC 2685, the prototype polar-ring galaxy. The spectroscopic data were acquired using the 6 m telescope of the Special Astrophysical Observatory of the Russian Academy of Sciences with the UAGS spectrograph and a scanning Fabry-Perot interferometer, while the photometric analysis was based on images from the Hubble Space Telescope archive. We demonstrate that the subsystem usually called the “inner polar ring” is a highly inhomogeneous gas and dust disk rotating approximately in the polar plane relative to the galaxy’s main body. When the self-absorption in the disk is taken into account, a comparison of its color indices with those from model computations of the color evolution of galaxies results in an age for the disk of about 1.4 × 109 years, much lower than the previously accepted estimate.