Schematic diagram of the radial bins (divided by solid black lines) and the four regions based on the TIR flux density (see Sect. 2.3 and Fig. 1) that we use in our analysis to search for regional variations in the gas properties. Labels A-D mark positions of the typical line spectra shown in Fig. 3. The dashed grey lines demarcate the coverage of the PACS and SPIRE spectroscopic maps for reference.