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 HI data available for a sample ofthese peculiar objects. The total K-band luminosity, which mainly comes fromthe central host galaxy, and the measured HI linewidth at 20% of the peak lineflux density, which traces the potential in the polar plane, place most polarrings of the sample far from the Tully-Fisher relation defined for spiralgalaxies, with many PRGs showing larger HI linewidths than expected for theobserved K band luminosity. This result is confirmed by a larger sample ofobjects, based on B-band data. This observational evidence may be related tothe dark halo shape and orientation in these systems, which we study bynumerical modeling of PRG formation and dynamics: the larger rotationvelocities observed in PRGs can be explained by a flattened polar halo, alignedwith the polar ring.Comment: 22 pages, 8 postscript figures, accepted for publication in Astrophysical Journa