Left: distributions of the mean Doppler velocity Δv (km s^-1) measured with respect to its value averaged over the whole map (shown as “reference” in Fig. 12). The black curve shows a two-Gaussian common fit to the two distributions. Right: dependence of the projection of the mean Doppler velocity Δv (km s^-1), averaged over pixels, included in the bands shown in Fig. 14, on coordinate ξ measured from south-east to north-west. The black curve shows a polynomial common fit to the two distributions. In both panels, the CO(1−0) data are shown in red and the CO(2−1) data in blue.