Top: M 31 central region thermal–MIR correlation. Bottom: M 31 central region nonthermal–MIR correlation. It is evident, especially from the bottom panel, that the scatter plots show sharp edges. This comes naturally from the fact that the central region points are distributed over a circular area with sharp edges. Log–log slopes for thermal and nonthermal emission in the central region are respectively 1.80 ± 0.06 and 1.07 ± 0.02. Only pixels above 3σ have been used.