  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% (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. Twenty-three
sources are found to have substantial absorption and intrinsic X-ray
luminosities greater than 10^44 erg/s, 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 ultra-deep 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 ~75% of the AGN population is heavily absorbed at all
luminosities and redshifts.
