New candidates to polar-ring galaxies from the Sloan Digital Sky Survey

Abstract

Polar-ring galaxies (PRGs) are fascinating systems in which the central object (typically, an early-type galaxy) is encircled by a large-scale ring of stars, gas, and dust with almost perpendicular spin. PRGs are rare objects and their formation mechanism is not entirely clear. In this paper, we present a new sample of 31 candidates to PRGs identified in the Sloan Digital Sky Survey (SDSS). Using their stacked $gri$ images, we determined geometrical parameters of these galaxies (the position angle and the size of the host galaxy and the ring). We compare our sample objects to the previously known PRGs and discuss their general characteristics (the frequency of faint outer structures, the luminosity--size relation, and the distribution by the apparent angle between the ring and the host galaxy). Our main results are: (i) Central galaxies of PRGs follow the luminosity--size relation for ordinary galaxies. The ring components are located along the similar relation but with a larger scatter. This increasing scatter may be the result of a secondary origin of polar structures. (ii) At least half of PRGs show a ring component within 20$^\circ$ from the perpendicular orientation.