Line profiles of the [O i] 63 and 145 μm (a and b) transitions compared with those of some OH lines (c)–f)). Upper histograms, NGC 4418; lower histograms, Arp 220. Model predictions are also included. For NGC 4418, the blue curves show the combined contribution of the C_core and C_warm components, and the green curves show the model for C_extended . For Arp 220, see caption of Fig. 6. Red denotes the total of all components.