Scatter density plots between different stellar and dust quantities from the M 81 dust cell data. Spearman rank correlation coefficients are shown at the top of each panel, and power-law fits through the data are shown as black lines. Top left panel: dust luminosity density as a function of star-formation rate density, with f_young on the auxiliary axis. Top right panel: correlation between dust mass density and star-formation rate density. Bottom left panel: both the star-formation rate and the dust luminosity plotted per unit of dust mass, with the heating fraction on the auxiliary axis. The dotted green line is the power-law fit through the points with f_young >  0.8. Bottom right panel: correlation between the diffuse stellar mass density and the density of star-formation rate (ρ_SFR).