2000MNRAS.314...11B

We present and discuss observations of the radio galaxy 0755+379 made with the VLA at 1.4 and 5.0GHz and with MERLIN at 1.7GHz. These data allow us to image the radio jets over two orders of magnitude in linear size and to investigate the hypothesis that jets in low-luminosity radio galaxies start with velocities close to c and then slow down to subrelativistic speeds. We apply a model for an adiabatically expanding relativistic jet to the observed surface brightness and derive velocity profiles along the jet for various assumed starting conditions. We show that these profiles are consistent with the observed jet/counter-jet brightness ratios provided that the angle to the line of sight θ≃27°. The inferred velocity at a distance of 0.5kpc from the nucleus is ≃0.9c. Finally, we show that the predicted velocity at 10kpc from the nucleus is consistent with that obtained independently from energy-balance arguments.