The ultra-deep XMM survey in the CDFS: X-ray spectroscopy of heavily
  obscured AGN
  We present selected results on the X-ray spectroscopy of distant, obscured
AGN as obtained with the ultra-deep (~3 Ms) XMM-Newton survey in the Chandra
Deep Field South (CDF-S). One of the primary goals of the project is to
characterize the X-ray spectral properties of heavily obscured and
Compton-thick AGN over the range of redshifts and luminosities that are
relevant in terms of their contribution to the X-ray background. The ultra-deep
exposure, coupled with the XMM detector's spectral throughput, allowed us to
accumulate X-ray spectra for more than 100 AGN to investigate the absorption
distribution up to z~4.
