Silicate apparent depth at 9.7 μm, τ_9.7, versus the EW of PAH at 6.2 μm, EW(PAH 6.2 μm), for PG QSOs, S1s, and SBs (left) and for LINERs and S2s, (right). LINER1s, LINER2s, S1s, S2s, PG-QSOs, and SBs are shown with purple and pink circles, red and yellow squares, orange stars, and green upside-down triangles, respectively. White circles and white stars denote known Compton-thick sources and Compton-thick candidates, respectively. The error bars in τ_9.7 are always within the size of the symbol. In the right panel we also include PG QSOs, S1s, and SBs with white symbols for comparison purposes. Green-dotted lines indicate the diagonal branch found by Spoon et al. (2007) for ULIRGs and SBs. The shadowed (grey) area shows the range of values for τ_9.7 that could be explained with clumpy models (Nenkova et al. 2008). We also use orange and yellow lines to show the expected range of values for τ_9.7 in face-on AGN (assuming i = 0°) and in edge-on AGN (assuming i = 90°) using the models described by Nenkova et al. (2008) (see text). The short red vertical line shows EW(PAH6.2 μm) = 0.228 μm, which divides into weak and strong PAHs.