B2 1144+35: A giant low-power radio galaxy with superluminal motion

We report on centimeter VLA and VLBI observations of the giant, low-power radio galaxy B2 1144+35. These observations are sensitive to structures on scales of from less than 1 pc to greater than 1 Mpc. Diffuse steep-spectrum lobes on the megaparsec scale are consistent with an age of similar to 10(8) yr. On the parsec scale, a complex jet component is seen to move away from the center of activity with an apparent velocity of 2.7 h(50)(-1) c. It shows a central spine-shear layer morphology. A faint parsec-scale counterjet is detected, and an intrinsic jet velocity of 0.95c and an angle to the line of sight of 25 degrees are derived, consistent with an intrinsically symmetric ejection. The central spine in the parsec-scale jet is expected to move at a higher velocity, and a Lorentz factor of gamma similar to 15 has been estimated near the core. The age of this inner VLBI structure is similar to 300 yr. Assuming a constant angle to the line of sight, the jet velocity is found to decrease from 0.95c at 20 mas (32 pc on the plane of the sky) to 0.02c at 15 ' (24 kpc on the plane of the sky). These findings lend credence to the claim that (1) even the jets of low-power radio galaxies start out relativistic and (2) these jets are decelerated to subrelativistic velocities by the time they reach kiloparsec scales.