HST AND MERLIN OBSERVATIONS OF 3C-264 - A LABORATORY FOR JET PHYSICS AND UNIFIED SCHEMES

We present new HST optical continuum and emission line WFPC2 images an d MERLIN radio observations of 3C 264 at similar to 0.'' 1 resolution. The jet is well resolved in both the optical and radio images. In add ition, we report the discovery of an apparent optical ''ring'' at a pr ojected radius of similar to 300-400 pc. The ring is most likely the m anifestation of absorption by a nearly face-on circumnuclear dust disk . We discuss the evolution of the jet properties with distance. The je t collimation, brightness, and orientation change dramatically as it c rosses the outer boundary of the ''ring'' suggesting an interaction be tween the jet and dense circumnuclear gas. We present a model for the jet propagation in which an initially relativistic jet decelerates as it crosses through a region of dense cold gas in the inner region of t he galaxy. We derive the equations for brightness variations along an adiabatically expanding relativistic jet, and we model the jet brightn ess in 3C 264 as the combined effects of Doppler boosting, and adiabat ic losses as traced through the jet velocity and width. We find that t he data are consistent with a model in which the jet is initially high ly relativistic (upsilon similar to 0.98c, gamma = 5) and we view it a t roughly 50 degrees inclination. We suggest that 3C 264 may serve as a laboratory for the study of relativistic entraining jets and may hel p us to understand the deceleration of jets, which is required in unif ying schemes for FRI radio galaxies and BL Lac objects.