nH_clump/nH_cloud = 5 simulation at t = 222 ky. Left: column density on a 0.4 × 0.4 × 0.4 pc³ box around the pillar structure in a face-on geometry. Right: mass-weighted histogram of the line-of-sight velocity in the same box (similar to optically-thin observational line spectra). Each spectrum is made on a square of 0.05 × 0.05 pc² drawn on the column density map. The spectra are drawn between  − 4 and 4 km s^-1 in 80 bins (horizontal axis) and the mass between 10^-4 and 1 solar mass (vertical axis in log scale). The lateral shocks can be clearly identified in the double wing spectra, which leads to a very broad line width.