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We present results on a search of heavily obscured active galaxies z>1.7using the rest-frame 9-20 keV excess for X-ray sources detected in the deepXMM-CDFS survey. Out of 176 sources selected with the conservative detectioncriteria (>8 sigma) in the first source catalogue of Ranalli et al., 46 objectslie in the redshift range of interest with the median redshift z~2.5. Theirtypical rest-frame 10-20 keV luminosity is 1e+44 erg/s, as observed. Amongoptically faint objects that lack spectroscopic redshift, four were found to bestrongly absorbed X-ray sources, and the enhanced Fe K emission or absorptionfeatures in their X-ray spectra were used to obtain X-ray spectroscopicredshifts. Using the X-ray colour-colour diagram based on the rest-frame 3-5keV, 5-9 keV, and 9-20 keV bands, seven objects were selected for their 9-20keV excess and were found to be strongly absorbed X-ray sources with columndensity of nH > 0.6e+24 cm-2, including two possible Compton thick sources.While they are emitting at quasar luminosity, ~3/4 of the sample objects arefound to be absorbed by nH > 1e+22 cm-2. A comparison with local AGN at thematched luminosity suggests an increasing trend of the absorbed source fractionfor high-luminosity AGN towards high redshifts.

The XMM deep survey in the CDF-S II. a 9-20 keV selection of heavily obscured active galaxies at z>1.7