THE RADIO JET IN NGC-6251

High-resolution observations are presented of the 300-kpc jet in the giant radio galaxy NGC 6251. The width of the jet is resolved over most of its length, and the axis of the jet wiggles with an amplitude increasing linearly with distance from the nucleus. Polarization data are used to derive densities of cold matter in the jet and, from the argument that the jet must form the lobe in a time equal to the age of the lobe, we estimate the speed of the jet as c/20. The energetics of the jet are then dominated by the bulk flow along it of cold matter at a rate of 1 Mo yr-1. The jet appears to be confined; the wiggle of its axis is probably due to oscillations of the direction of the collimator with a period of about 6 × 106 yr. © 1981 Royal Astronomical Society.