(top) and IR8 ratio (bottom) versus L[8 μm] for the local galaxy sample (ISO, AKARI, Spitzer-GOALS). Galaxies with compact mid-IR (more than 60% of the light emitted at 13.2 μm within the resolution element of 3.6″) and radio (Σ_IR  ≥  3  ×  10¹⁰ L_⊙) light distributions are marked with large filled red dots. Here the solid and dashed lines present the median and 68% dispersion around the Gaussian distribution as defined in Eq. (4).