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We present results from a spectral analysis of a sample of high-redshift(z>3) X-ray selected AGN in the 4 Ms Chandra Deep Field South (CDF-S), thedeepest X-ray survey to date. The sample is selected using the most recentspectroscopic and photometric information available in this field. It consistsof 34 sources with median redshift z=3.7, 80 median net counts in the 0.5-7 keVband and median rest-frame absorption-corrected luminosity $L_{2-10\rmn{keV}}\approx1.5\times10^{44}\rmn{erg} \rmn{s^{-1}}$. Spectral analysis forthe full sample is presented and the intrinsic column density distribution,corrected for observational biases using spectral simulations, is compared withthe expectations of X-ray background (XRB) synthesis models. We find that$\approx57$ per cent of the sources are highly obscured($N_H>10^{23}\rmn{cm^{-2}}$). Source number counts in the $0.5-2\rmn{keV}$ banddown to flux $F_{0.5-2 \rmn{keV}}\approx4\times10^{-17}\rmn{erg}\rmn{s^{-1}cm^{-2}}$ are also presented. Our results are consistent with adecline of the AGN space density at z>3 and suggest that, at those redshifts,the AGN obscured fraction is in agreement with the expectations of XRBsynthesis models.

The high-redshift (z>3) AGN population in the 4 Ms Chandra Deep Field South