MERLIN OBSERVATIONS OF SUPERLUMINAL MOTION IN THE JET OF 3C120

We present evidence for changes in the radio structure of the jet in 3C120 between 1980 December and 1988 December derived from MERLIN observations at 1.67 GHz. The changes are consistent with outward motion of 19 +/- 3 mas (2.4 +/- 0.4 mas yr-1, i.e. 3.7 +/- 0.6 h-1 c, for H0 = 100 h km s-1 Mpc-1) in the inner jet, about 0.15 arcsec (approximately 75 h-1 pc) from the core. This confirms the suggestion by Benson et al. that the jet does not slow down quickly just outside the core region usually imaged by VLBI. However, we find no evidence for motion at the position of the knot 4 arcsec approximately 2 h-1 kpc) from the nucleus as suggested by Walker et al. Our limit is < 1.25 mas yr-1, i.e. < 1.9 h-1 c, compared with Walker's et al.'s measurement of 2.4 +/- 0.8 mas yr-1, i.e. 3.7 +/- 1.2 h-1 c.