Slice along the major axis of the total intensity CO(J = 3–2) distribution shown in Fig. 1, averaged over a width 11 arcsec (3 pixels) in z. East is on the left and west is on the right. Offsets are with respect to the IR centre (Table 1). The thin red curve shows a Gaussian ring with parameters as given in Table 3. The inset shows the residuals (data–model) for the central molecular ring.