a: left: PAH 6.2 μm luminosity versus the total IR luminosity. Blue squares represent AGN, red stars SFGs, and black circles show the sample of Gruppioni et al. (2016). The dashed blue line represents the linear relation for AGN, the dot-dashed red line the relation for SFG, and the black solid line the relation for the Gruppioni et al. (2016) sample. b: centre: [SIV]10.5 μm luminosity versus the total IR luminosity. c: right: PAH 11.3 μm luminosity versus the total IR luminosity. In all three figures, the Gruppioni et al. (2016) sample was limited to AGN fractions > 0.4 in the 5−40 μm spectral interval (see Sect. 4.3).