Left: H¹³ CO⁺(1−0) integrated intensity map (colour scale) obtained towards the velocity range 42−48 km s⁻¹. The zero level of the colour bar corresponds to 3σ(σ=0.1 K km s⁻¹). The yellow line indicates the path used to extract the pv diagrams shown in Fig. 3. Along this curve, the intermediate endpoints are marked as A₀ and A₁. The beam size is indicated in the bottom right of the map. The location of the massive cores within the cloud is indicated with light green crosses (Rathborne et al. 2006; Butler & Tan 2012). Right: velocity map (colour scale) of the H¹³ CO⁺(1−0) emission with the dense gas tracer and mass surface density emission contours superimposed as in the left panel. Only pixels with an integrated intensity above 3σ are shown. The north and east directions are indicated in the bottom right corner. In both panels, the SiO emission contours, from 3σ(σ=0.07 K km s⁻¹) by steps of 3σ, and the 0.1 g cm⁻² mass surface density contour (visual extinction ∼20 mag) are superimposed (Kainulainen & Tan 2013).