Compton thick active galactic nuclei in Chandra surveys

We present the results from an X-ray spectral analysis of active galactic nuclei (AGN) in the Chandra Deep Field-South, AEGIS-XD and Chandra-COSMOS surveys, fo- cussing on the identication and characterisation of the most heavily obscured, Comp- nd evidence that the covering factor of the obscuring material decreases with LX for all redshifts, consistent with the receding torus model, and that this factor increases with redshift, consistent with an increase in the obscured fraction towards higher redshifts. The strong relationship between the parameters of obscuration and LX points towards an origin intrinsic to the AGN, however the increase of the covering factor with redshift may point towards contributions to the obscuration by the host galaxy. We make NH, (with uncertainties), observed X-ray uxes and intrinsic 2-10 keV luminosities for all sources analysed in this work publicly available in an online catalogue.