Crux tangency emission spectra showing [C ii], H i, and ¹²CO emission plotted against velocity (V_LSR). The spectra are averaged over the longitude range indicated. Note that the intensity scale is normalized to the peak emission within the velocity range. The corresponding 1–σ error bars are indicated in the [C ii] and ¹²CO spectra at V_LSR = 50 km s^-1. The tangent velocity is also marked. The dashed lines indicate the [C ii] excess beyond the tangent velocity and ¹²CO peak in the spectra.