is $N_{\rm\,H}\sim10^{22}\rm\,cm^{-2}$, while the torus is believed to have larger values of the equatorial column density, and that this obscuration might be related to the presence of dust lanes or molecular structures in the host galaxy (e.g., [@Matt:2000kx]). However, @Bianchi:2009fk, using the results of @Della-Ceca:2008fk, have showed that a similar decrease of $f_{\mathrm{obs}}$ with the luminosity is obtained when setting this threshold to a larger value of line-of-sight column density. They found that the fraction of CT objects decreases with the luminosity as $f_{CT}\propto L^{-0.22}$, similarly to what is found for $f_{\mathrm{obs}}$ in the X-rays (e.g., [@Hasinger:2008ve], see Eq.\[Eq:Hasinger\]). A similar result was obtained by @Fiore:2009fk from a [*Chandra*]{} and [*Spitzer*]{} study of AGN in the COSMOS field. This implies that the contribution of dust lanes or of galactic molecular structures to the observed $N_{\rm\,H}$ does not affect significantly the $f_{\mathrm{obs}}-L_{\mathrm{X}}$ relationships obtained in the X-rays.

The equatorial column density of the torus
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![Iron K$\alpha$ $EW$ versus X-ray luminosities and predicted trends obtained for different values of the equatorial column density of the torus. The points are the values of the equivalent width of the iron K$\alpha$ line reported by @Shu:2010zr, obtained by averaging multiple [*Chandra*]{}/HEG observations of AGN. 