Left: column density in a 0.7 × 1.4 × 0.5 pc³ box around the pillar structure at t ≈ 710 ky. Right: mass-weighted histogram of the line-of-sight velocity in the same box (similar to the optically thin observational line spectra). Each spectrum is made on a square of 0.1 × 0.1 pc² drawn on the column density map. The spectra are drawn between − 4 and 4 km s^-1 in 80 bins (horizontal axis) and for mass between 10⁴ and 1 solar masses (vertical axis in log scale). The lateral shocks have collided to form the pillar, the spectra now being peaked around 0 km s^-1.