The distribution of absorption in AGN detected in the XMM-Newton observations of the CDFS

We have used very deep XMM-Newton observations of the Chandra Deep Field-South to examine the spectral properties of the faint active galactic nucleus (AGN) population. Crucially, redshift measurements are available for 84 per cent (259/309) of the XMM-Newton sample. We have calculated the absorption and intrinsic luminosities of the sample using an extensive Monte Carlo technique incorporating the specifics of the XMM-Newton observations. 23 sources are found to have substantial absorption and intrinsic X-ray luminosities greater than 10(44) erg s(-1), putting them in the 'type-2' QSO regime. We compare the redshift, luminosity and absorption distributions of our sample to the predictions of a range of AGN population models. In contrast to recent findings from ultradeep Chandra surveys, we find that there is little evidence that the absorption distribution is dependent on either redshift or intrinsic X-ray luminosity. The pattern of absorption in our sample is best reproduced by models in which similar to 75 per cent of the AGN population is heavily absorbed at all luminosities and redshifts.