Temperature ratio map and column density maps at different temperatures. Top panel: ratio map of the temperatures derived from the Herschel far-infrared data (Fig. 3; Marsh et al. 2017) vs. the temperature map obtained from the HCN/HNC ratio (Fig. 11). For this ratio map, the HCN and HNC data were first smoothed to the 12″ resolution of the dust temperature map. The black contours show the H₂ column density map derived by Marsh et al. (2017) at contour levels between 10²² and 5 × 10²² cm⁻² (step 1 × 10²² cm⁻²). A linear scale-bar is shown to the left. The bottom three panels show the H₂ column densities derived at different temperatures (as marked in the panels) as outlined in Marsh et al. (2017). The six main regions A to F are marked in all panels.