We report the results of new spectral and photometric observations of a sample of northern polar-ring galaxies (PRGs). We found that the nuclei of galaxies with a forming polar ring have both higher Hα equivalent width and luminosity and show enhanced star formation. We also find an excess of active nuclei (Sy or LINER) among forming PRGs. From the optical colours and Hα luminosities of the rings, we infer that the rate and IMF of star formation in the polar rings are similar to those in normal late-type spiral galaxies.

Introduction

Polar-ring galaxies (PRGs) are among the most interesting and spectacular relics of gravitational interactions between galaxies. The existence of prominent rings of gas, dust and stars aligned roughly in a perpendicular orientation with respect to the major axis of the main galaxy has provided a new opportunity to study the dynamical structure and evolution of galaxies. According to the most popular point of view, the observed structure of PRGs is the result of galaxy interactions ranging from a gas accretion to a complete merger.

With the goal of a detailed study of PRGs we undertook observations of a restricted sample of northern PRGs from the catalogue by Whitmore et al. (1990) using the 6-m telescope of the Special Astrophysical Observatory of the Russian Academy of Sciences for the CCD photometry in the B, V, and Rc bands (this work is now in progress) and the 1.93-m telescope of the Observatoire de Haute-Provence (spectral observations of 16 PRGs in the range 6200–7170 Å).