Overlay between H I (black) and [C II] (red) spectra at an angular resolution of 2′ in a grid of 2′. The PDR ring of RCW 120 is indicated with a dashed black circle and the O star with a black star symbol. The velocity and temperature ranges are given in the upper caption. This plot is intended to show qualitatively that thereis a systematic H I depression at velocities around the bulk emission velocity of the cloud at − 8 km s⁻¹. The [C II] line shows self-absorption at that velocity (and flat-top spectra) which is not so prominent in this display because the spectra are smoothed to 2′ resolution.