Fig. 5. The line centre velocity of the HCO [FORMULA] emission line component. The light regions represent blueshifted gas whilst the dark regions represent redshifted gas. The contour levels are from [FORMULA] km s-1 in increments of 0.2 km s-1. The markers have the same significance as in Fig. 2. The beamsize is indicated in the top left of the figure. The data are from Paper I.