Maps of indicators of the interstellar gas properties: the [Oi]145/[Oi]63 line ratio for tracing the gas temperature (left), the [Oiii]88/[Oi]63 line ratio as a tracer of the ionised gas fraction (middle), and the [Oiii]88/[Nii]122 ratio for deriving the stellar effective temperatures of the ionising sources (right). The maps are centred on , (J2000.0) and are presented in the resolution and pixel size of the PACS 160 μm map. Contours from the F_TIR map (see Fig. 1) are superimposed on each image as a visual aid with levels as listed in Fig. 4.