The transverse velocity structure of the HH 111 jet

We present long-slit spectroscopic observations of the HH 111 jet obtained with the 4.2 m William Herschel Telescope. We have obtained spectra for slit positions along and across the jet axis, in order to search for radial velocity, electron density and excitation variations across the jet. We have detected faint emission across knots HH 111 D and F, extending to large (approximate to 15 ") distances from the flow axis. This extended emission shows a radial velocity stratification, with higher radial velocities oil the jet axis and lower velocities away from the axis. Knot D has a low central electron density surrounded by material with higher electron densities, while the electron density is approximately constant across knot F. We argue that the extended emission and the radial velocity variations observed across the HH 111 flow are compatible with a jet beam with a transverse gradient in velocity or with a jet which is entraining low velocity material.