Distribution of the observed (i.e., not corrected for absorption/extinction) rest-frame 2–10 keVto [Ne v] luminosity ratio (X/NeV) for the 69 zCOSMOS type 2 AGN with reliable X-ray photometry (23 X-ray detections and 46 upper limits, see Sect. 5.1 for details). The filled histogram represents the X-ray-detected objects, while the histogram delimited by the solid line shows the luminosity ratio upper limits for X-ray-undetected type 2 AGN. The vertical dashed line indicates the threshold defined by Gilli et al. (2010): objects to the left of this line are candidate Compton-thick AGN. The filled circle indicates the average value obtained from stacking the sample of 46 X-ray-undetected type 2 AGN.