H I position-velocity diagrams along the three paths shown in red in the bottom-left panel. The diagrams are drawn using a width of ∼20″, twice the 11″ angular resolution of the H I cube used here. For visualisation purpose we binned the channels by a factor of 3 compared to the specs given in Sect. 2, resulting in a channel width of 4.1 km s⁻¹. The three diagrams begin from the point labelled as “start” in the bottom-left panel and have a common first half, which consists of two straight segments. The end of these two segments is represented by the vertical dashed lines in the diagrams. The linear colour-scale of the diagrams ranges from −2σ to +8σ, where σ is the noise level. The white contours start at a +10σ level and increase by a factor $\sqrt{2}$ at each step. The colour-scale and contours of the bottom-left panel are as in Fig. 3.