Meudon PDR modeling of ([OI] 145 μm+[CII] 158 μm)/FIR luminosity (blue), [OI] 145 μm/[CII] 158 μm (red), and [CII] 158 μm/[CI] 370 μm (green). This particular example is for the region at (RA, Dec) = (05^h39^m43^s, −69°45′43′′), which corresponds to the pixel [−1, 1] in Figs. 8 and 12. Each of the observed line ratios is shown as the solid line, while the 1σ uncertainty is in dotted line. The best-fit solution with the minimum χ² is indicated as the black cross. Finally, the following model parameters are used for each plot: A_V = 0.5 mag and G_X = 0 (top left), A_V = 0.5 mag and G_X = 10 (top right), A_V = 1 mag and G_X = 0 (bottom left), and A_V = 1 mag and G_X = 10 (bottom right). Note that the circular contours in the top left (P/k> 10⁷ K cm^-3 and G_UV ~ 500) and bottom right (P/k ~ 10⁵ K cm^-3 and G_UV ~ 10⁴) plots are artifacts due to the unavailability of model predictions over the corresponding parameter ranges.