Rest-frame (uncorrected for absorption) L_X vs. L_6 μm luminosity diagram. The large filled circles (blue) correspond to the bright sources (f_2 − 10 > 10^-15 erg cm^-2 s^-1), while the small circles (magenta) correspond to the fainter sources. The red squares correspond to the two bona fide Compton-thick AGN from the 3 Ms XMM observations (Comastri et al. 2011), while the red-star denotes the source CDFS-309, which was proposed as a Compton-thick AGN by Feruglio et al. (2011). The crosses refer to the 20 candidate Compton-thick sources of Tozzi et al. (2006) in the 1 Ms CDFS observations. These include both the reflected as well as the transmission-dominated sources; two sources not detected in Luo et al. (2008) and two more sources detected in fewer than four IRAC bands have been excluded. The red triangles correspond to the five low-luminosity sources (L_X < 10⁴² erg s^-1) with flat spectra, given in Table 4. The solid line denotes the L_X/L_6 μm average Compton-thick AGN relation; this has been derived from the average AGN relation of Fiore et al. (2009), scaled down to the expected Compton-thick AGN X-ray luminosity, assuming a 3% fraction of torus reflected emission relative to the intrinsic 2–10 keV luminosity. The dashed line shows the luminosity-dependent Compton-thick average L_X/L_6 μm relation for an 1% torus-reflected emission.