Stacking centred at − 144.3 km s^-1 of each ¹³CO(2–1) velocity component with v> −300 km s^-1. The ¹³CO component is displayed in red (at − 144 km s^-1). There is a component (displayed in green at − 1285 km s^-1) in C¹⁸O which appears at the same velocity. The lines adjustment are displayed in blue. The velocity ranges corresponding to the two lines are displayed as rectangles. Standard weights (∝ T_intδv/T_sys²) for each observation have been used for the averaging.