Comparison of observed scalings to two component toy models. Red lines show the fits to the data as previously shown in Fig. 6 (here: left and center panel) and Fig. 8 (right panel). Both toy models include a mix of a “disk” component with cold dust and a high ratio [Cii]/FIR, and a “dense star formation” component with warm dust and low [Cii]/FIR, with varying surface brightness of the warm component. Spreading the dense SF component with low filling factor over a large disk is a very poor fit, while scaling down its size with surface brightness gives a first approximation to the data.