Solid curves represent the first moments of several CH₃CN(12–11) components (indicated in the top left of each panel) estimated along a cut through the continuum peak (α(J2000) = 18^h47^m3431 δ(J2000) = –01°12′460) with PA = –22°, i.e. perpendicular to the velocity gradient in Fig. 5. The dashed curves are the zero moments of the corresponding lines.