2010MNRAS.401.2067B

We show that an object classified as a galaxy in on-line data bases and revealed on sky survey images as a distant ring galaxy is a rare case of polar ring galaxy (PRG) where the ring is only slightly inclined to the equatorial plane of the central body (CB). Imaging information from the Sloan Digital Sky Survey (SDSS) indicates that the diameter of the ring is about 36 kpc. The SDSS data was combined with long-slit spectroscopic observations and with Fabry-Pérot interferometer Hβ mapping obtained at the Russian Academy of Sciences 6-m telescope. We derived the complex morphologies of this presumed ring galaxy from a combination of SDSS images and from the kinematical behaviour of the CB and of the ring, and determined the stellar population compositions of the two components from the SDSS colours, from the spectroscopy and from models of evolutionary stellar synthesis. The metallicity of the ring material is slightly underabundant. The total luminosity and the total mass of the system are not extreme, but the rather high M/L ≃ 20 indicates the presence of large amounts of dark matter. We propose two alternative explanations of the appearance of this object. One is a ring formed by two semicircular and tight spiral arms at the end of a central bar. The apparent inclination between the ring and the CB, and a strange kink at the north-east end of the ring, could be the result of a warp or of precession of the ring material. The object could, therefore, be explained as an extreme SBa(R) galaxy. The other possibility is that we observe a PRG where the inner object is an S0 and the ring is significantly more luminous than the central object. The compound object would then be similar to the NGC 4650A galaxy, but then it would be a rare object, with a polar component only modestly inclined to the equatorial plane of the CB. Arguments for (and against) both explanations are given and discussed, with the second alternative being more acceptable.