CLOUDY CO(1−0)-normalized SLED models in the PDR (left panels) and XDR regime (right panels) for which the intensity of the incident radiation field was varied over the entire parameter space and for two reference values of total hydrogen density (n_H = 10^2.9, 10^5.1 cm⁻³) and column density N_H = 10²³ cm⁻². PDR cases are shown in blue, and XDRs are in red. Both are color-coded according to the values of the radiation field flux. The dashed gray line indicates the J³ curve, which is the expected trend of the CO SLED in LTE (in the optically thick and high-temperature or low-frequency limit).