ИСТИНА

Galaxies with polar rings (PRGs) are an interesting case of peculiar systems that reveal outer rings or of gas, dust and stars, rotating in the plane approximately perpendicular to the disc of the main galaxy. Recently, Moiseev et al. (2011) have published a catalogue of polar-ring galaxies selected from the SDSS (the SDSS-based polar rings catalogue=SPRC). Now we analyze the main structural parameters of the SPRC best candidates, also including some galaxies from the Whitmore et al. (1990) catalogue. The size and apparent ellipticity of central galaxies and outer components were estimated based on the elliptical approximation of the SDSS isophotes. We show that most of the outer structures throughout our sample are really polar, i.e. mutual inclination between the outer ring/disc and central galaxy exceeds 70 degrees. An overall histogram of relative diameters both for the inner and outer polar structures has a bimodal shape which can be explained by the fact that middle-sized structures are short-lived, because the stability of inner polar rings and discs are supported by the bulge gravitation, whereas the outer large-scale structures are stabilized in the triaxail dark halo.