Two pv diagrams of the protrusion. Top: selected crosscuts along the green arrows overlaid on the integrated [C II] intensity map. The number of the crosscuts is indicated at the starting point of the cut. Middle and bottom: pv diagrams generated along the magenta crosscuts (cuts 8 and 23, respectively). The pv diagrams with horizontal green lines both show the [C II] emission produced by the FUV-illuminated surface of OMC, and the arcuate white and yellow lines trace the shell expanding at 12 km s⁻¹ and 6 km s⁻¹, respectively. The pv diagrams in Figs. B.9 and B.10 have the same scale on both axes. A ¹²CO-pv diagram along crosscut 23 is shown in Fig. B.8 for comparison with [C II].