Integrated dust and PAH emission SEDs for the diffuse component, for model galaxies with different face-on opacities (plotted as different curves in each panel). All models shown in this figure are for pure disk galaxies (B/D = 0.0). From left to right the panels show model galaxies with various levels of contribution from the old stellar populations (old = 0.1 (0.0), old = 2.0 and old = 20.0). From top to bottom the panels show models with various levels of SFR (SFR′ = 0.0,2.0,20.0   M_⊙/yr). The colour coding is as follows: green is for , red is for , blue is for and black is for .