Dumbbell Galaxies And Precessing Radio Jets
Astron. J., 87, 602-615, 1982, with J. S. Gallagher and A. Wirth.
Abstract
We have compiled a catalog of —100 close double elliptical galaxies which are radio sources. Many of these are dumbbell galaxies, i.e., two nearly equally bright elliptical galaxies in a common envelope. We argue that the close proximity of the galaxies (~ l()-30 kpc) will dynamically affect the radio jet through gravitational interactions with its confining gas cloud. The double galaxies may be either in highly eccentric (or unbound) orbits or in circular orbits. In the first case, an impulsive interaction can lead to inversion-symmetric jets, such as in NGC. In the second case, the continuous tidal interaction can produce periodic mirror-symmetric wiggles in the radio jet. For high-velocity circular orbits, e.g., 3C 465, a wide-angle tail will occur, even though the center of mass of the dumbbell galaxy is at rest in the cluster. Our picture contributes to the growing evidence that the large-scale galactic gas distribution is equally as important as the central engine for determining jet properties, such as direction and collimation. We stress the current uncertainty in the nature of the underlying gravitational potential of these systems. Progress can be made by a careful program of observations using a morphological scheme we outline. We present the results of new optical observations on two prototypes for our scheme: NGC 326 and NGC 750/751.