Upper panels: (from left to right) Distribution of the emission in [O i] 63 μm, [O i] 145 μm, and the ratio of their intensities I([O i] 63 μm)/I([O i] 145 μm). The illuminating source, S 1, is depicted as a white star on the left side of the frames, being at the centre of the dashed circles. The white contours outline integrated N₂H⁺ (3–2) emission. Lower panels: distribution of the S(2), S(3), and S(5) pure rotational lines of H₂ are shown by the coloured maps, with the fluxes given by the scale bars. These data were obtained with the ISOCAM-CVF. The white contours and the symbols are as in Fig. 1. The graph shows the fit with the Meudon PDR code (Le Petit et al. 2006, red dots) to the dereddened observations for A_V = 6 mag. Blue data points are the observed values. Other H₂ lines, i.e. S(1) and S(4), are also filled in and shown as black dots.