The colour scale in the panels from left to right shows, respectively, the 0th (integrated intensity in T_MB), 1st (intensity-weighted centroid velocity structure), and 2nd moment (intensity-weighted linewidth structure) map of the 8.7-km s^-1 component ¹³CO(2−1) (top row) and C¹⁸O(2−1) emission (bottom row). The black contours in the upper panels, from left to right, go as follows: from 0.7 (3.2σ) to 7.0 K km s^-1 (32σ) in steps of 0.7 K km s^-1; from 7 to 9.5 km s^-1 in steps of 0.5 km s^-1; and from 1 to 4 km s^-1 in steps of 1 km s^-1. The corresponding contours in the lower panels are from 0.4 (2σ) to 3.2 K km s^-1 (16σ) in steps of 0.4 K km s^-1; from 7 to 9.5 km s^-1 in steps of 0.5 km s^-1; and from 0.5 to 2 km s^-1 in steps of 0.5 km s^-1. Superimposed on the maps are the LABOCA 870-μm contours in white as in Fig. 1. The yellow solid line on the top left and middle panels shows the location of the PV slice extracted for Fig. 7. The effective beam size of 30″ is shown in the upper left corner of the upper left panel.