Integrated line intensities predicted by the KOSMA-τ PDR model relative to the column density of the model clumps. The panels from left to right show CO 2−1, ¹³CO 2−1, C¹⁸O 2−1, [C I] 1−0, and [C II]. The white, gray, and black lines indicate the minimum, mean, and maximum of the observed ratio. For [C II], we only have an upper limit. For C¹⁸O 2−1, even the maximum falls outside of the covered parameter range and is lower than all displayed values. The red and orange contours indicate the lowest and highest column density in the region obtained from the dust observations.