Relationship between the X/O flux ratio and HR(2−4.5   keV/0.5−2   keV) hardness ratio, for X-ray emitters with optical counterparts in the SXDS (red stars) and GWS (black crosses) fields. Solid lines separate X-ray type-1 (unobscured) from both the X-ray type-2 (obscured) regions and the area with X/O  <  0.1, where Compton thick AGN, normal galaxies, and stars can be found (e.g. Fiore et al. 2003). The dashed line box shows the limits obtained by Della Ceca et al. (2004), where  ~85% of their spectroscopically identified AGN with broad emission lines have been found. In this work,  ~51% of the X-ray type-1 sources are located inside this box.