VLBI Observations of a Complete Sample of Radio Galaxies. VII. Study of the FR I Sources 3C 31, 4C 35.03, and 3C 264

We present results from global VLBI and VLA observations of three Fanaroff-Riley type I radio galaxies, 3C 31, 4C 35.03, and 3C 264, at a frequency of 5 GHz. In all three cases, we observe asymmetric parsec-scale structures consisting of a compact core and a single jet pointing in the direction of the more prominent kiloparsec jet. We interpret such alignment as evidence for the relativistic nature of FR I radio jets at parsec scales. Comparing the VLBI and VLA images of these sources, we find a progressive deceleration of the plasma flow from parsec to kiloparsec scales. We consider another five FR I radio galaxies studied previously by us and find that, in a set of eight FR I objects, the estimated jet bulk velocities and orientation angles with respect to the observer are consistent with the requirements of the unification model for low-power radio sources.