Polar ring galaxies and the Tully-Fisher relation: Implications for the dark halo shape

We have investigated the Tully-Fisher relation for polar ring galaxies (PRGs), based on near-infrared, optical, and H I data available for a sample of these peculiar objects. The total K-band luminosity, which mainly comes from the central host galaxy, and the measured H I line width at 20% of the peak line flux density, which traces the potential in the polar plane, place most polar rings in the sample far from the Tully-Fisher relation defined for spiral galaxies, with many PRGs showing larger H I line widths than expected for the observed K-band luminosity. This result is confirmed by a larger sample of objects, based on B-band data. This observational evidence may be related to the dark halo shape and orientation in these systems, which we study by numerical modeling of PRG formation and dynamics: the larger rotation velocities observed in PRGs can be explained by a flattened polar halo, aligned with the polar ring.