A VLA and VLBI proper-motion study of extragalactic jets: connecting the parsec and kiloparsec scales

Proper motions of extragalactic jets, primarily conducted with very long baseline interferometry (VLBI), have revealed that these jets have bulk relativistic velocities which can exceed 99.999% the speed of light (Lorentz factors up to ~80). The parsec-scale proper motions traced by VLBI observations, however, often show a flow that is still accelerating on these scales. The measurement of the full velocity profile of jets from parsec to kiloparsec scales has only been done for a handful of jets, owing to the difficulty of obtaining decades-long time baselines for comparison on the larger (kiloparsec) scales. The Very Large Array (VLA) has now been in operation for over 40 years, and the NRAO hosts a very rich archive of observations of extragalactic jets. I will present a new effort to mine the VLA archives to measure the proper motions of jet plasma on kilo-parsec scales, where I have analyzed archival VLA observations of radio-galaxies 3C78 and M87 for proper motions. For 3C78 we detect for the first time proper motions for multiple knots with speeds of 0.1-0.5c. Although sub-luminal, we find that the average kiloparsec velocity is ~ 3 times higher than the VLBI speeds, in keeping with observations of M87 and 3C 264 which have showed that the fastest bulk speeds in these FR I jets are reached on the > 100 parsec scale. I will conclude with a discussion of the prospects for radio and sub-mm wavelength proper-motion studies of jets and the large catalog we intend to build using new and archival data.