Hα+[NII] (left) and [NII] (right) intensities from Ciardullo et al. (1988) and Boulesteix et al. (1987) are displayed with an arbitrary normalisation in the top panels. The bottom left panel presents the CO velocities measured in this paper, superimposed on the gas kinematics based on (1) Hβ and  [Oiii]  lines measured in slits by Saglia et al. (2010), (2)  [Oii]  and  [Neiii]  measured in slits by Ciardullo et al. (1988) and (3) Hα and  [Nii]  measured in slits by Rubin & Ford (1971). The bottom right panel displays the velocity field obtained with  [Nii]  λ6584   Ȧ observations (cf. top right panel) based on a Fabry-Perot device by Boulesteix et al. (1987). On each panel, the positions of our CO observations are indicated with circles corresponding to the beams.