Panels a–f: velocity-integrated C¹⁸O (1–0) contours in the velocity ranges of 2–15 km s⁻¹, 15–21 km s⁻¹, 21–28 km s⁻¹, 30–44 km s⁻¹, 44–48 km s⁻¹, and 48–60 km s⁻¹ respectively, overlaid on the Spitzer 8 μm image. The white dashed lines in (d) show the filaments detected in 30–44 km s⁻¹, and the magenta dashed lines in (e) represent the cutting directions of Fig. 10. The colour bar represents the flux at 8 μm in units of Myr sr⁻¹.