1994A&A...291...57R

We have observed with long slit Hα spectroscopy 16 polar-ring galaxies or related objects. From the nuclear spectra, we find that these objects have enhanced nuclear activity with respect to normal galaxies. The objects identified as forming polar rings now, by gas accretion, have chaotic velocity fields. One of the objects - UGC 5600 - displays counter-rotating features. We also find that the global star-formation rate is enhanced in polar-ring galaxies with respect to normal isolated objects; their star-forming efficiency is comparable to that of the most strongly interacting samples. In the three settled polar-rings of our sample, we compare the rotation curves in the equatorial and polar planes. The maximum rotational velocities in the two planes are always comparable, although they are not measured at the same radii. In the two galaxies UGC 7576 and UGC 9796, we build mass models after fitting luminosity profiles of the bulge, disk and polar rings. We are not able to account for the rotational velocities in the ring without adding dark matter, even taking into account the large gas masses detected. The required amount of dark mass reaches 1.6 and 3 the luminous mass in UGC 7576 and UGC 9796, inside radii of 17 kpc and 21.4 kpc respectively. We cannot constrain the 3D shape of the dark halo, since equatorial and polar velocities are not measured at the same radii in the outer parts. This is a general impossibility in polar-ring systems, since there cannot exist gas in the outer parts at the same radii as the ring itself, which is formed out of gas. This unfortunately prevents any direct determination of the dark halo flattening in spiral galaxies.