[C II]/FIR versus CO(2−1)/FIR in M42 (top left: Veil Shell, bottom left: OMC4 with OMC1 (in gray scale; black-edged red points lie to the west of Orion S)), M43 (top right) and NGC 1977 (bottom right). The color scale in M42 indicates the distance from θ¹ Ori C. The division of M43 and NGC 1977 into the regions given in the legend is described in Sect. 3.2. Dashed lines are edge-on model outputs with the parameters (G₀, n, A_V,los) given in thelegend. Dashed dotted lines in the OMC4 and the M43 panels are face-on model outputs for the densities given in the legend. gray points in M43 correspond to the estimated intensities of the background PDR toward the center of M43.