KINEMATIC PROFILES OF DUMBBELL GALAXIES WITH TWISTED RADIO JETS

We study the orbital properties of dumbbell galaxies which harbor twis ted radio jets. Velocity and velocity dispersion profiles for four dum bbell pairs (3C66B, 3C75, 3C449, 0326+39) are presented. We analyze op tical CCD images in search of isophote off-centering and large isophot e twists. Combining the kinematic and isophotal information, we discus s whether each system is an interacting pair, and derive constraints o n the relative orbit. The types of isophotal distortions, combined wit h the prograde/retrograde nature of the relative orbit, suggest that t hree of the objects (3C66B, 3C75 and 0326+39) are unlikely to be in ci rcular orbits. Only 3C449 may be in a close, moderate-ellipticity orbi t. We find that the distribution of relative velocity with separation for dumbbells with distorted radio morphology from the catalogue of Pa rma et al. (1991) also suggests a prevalence of eccentric orbits. We d iscuss that dumbbells with distorted radio morphology may deviate sign ificantly from the circular orbit model proposed by Valentijn & Casert ano (1988). The genesis of radio distortions could be related to such distinct orbital behaviour. The amplitude and wavelength of jet oscill ations in these objects correlates with the projected separation of th e pairs, pointing at a dynamical origin for the jet oscillations. Howe ver, for three of the four systems studied in detail here, the jet osc illations cannot be easily traced to orbital displacements of the pare nt galaxies. Either interactions trigger radio beam precession, or the intracluster medium plays a role in setting the radio beam oscillatio ns.