Integrated dust and PAH emission SEDs for the diffuse component, for model galaxies with different bulge-to-disk ratios (plotted as different curves in each panel). All models shown in this figure are for galaxies with a fixed contribution from the old stellar population (old = 2.0). From left to right the panels show model galaxies with various levels of SFR (SFR′ = 0.0, SFR′ = 2.0 and SFR′ = 20.0). From top to bottom the panels show models with various face-on B band opacities (, , and ). The colour coding is as follows: green is for B/D = 0.0, red is for B/D = 0.5, blue is for B/D = 1.0 and black is for B/D = 2.0.