We present results on a search of heavily obscured active galaxies z > 1.7 using the rest-frame 9-20 keV excess for X-ray sources detected in the deep XMM-CDFS survey. Out of 176 sources selected with the conservative detection criteria (>8σ) in the first source catalogue of Ranalli et al. (in prep.), 46 objects lie in the redshift range of interest with the median redshift ˜ z≃ 2.5 ≃ 2.5. Their typical rest-frame 10-20 keV luminosity is 1044 erg s-1, as observed. Among optically faint objects that lack spectroscopic redshift, four were found to be strongly absorbed X-ray sources, and the enhanced Fe K emission or absorption features in their X-ray spectra were used to obtain X-ray spectroscopic redshifts. Using the X-ray colour-colour diagram based on the rest-frame 3-5 keV, 5-9 keV, and 9-20 keV bands, seven objects were selected for their 9-20 keV excess and were found to be strongly absorbed X-ray sources with column density of NH ≥ 0.6 × 10^24 cm-2, including two possible Compton thick sources. While they are emitting at quasar luminosity, ~3/4 of the sample objects are found to be absorbed by NH > 10^22 cm-2. A comparison with local AGN at the matched luminosity suggests an increasing trend of the absorbed source fraction for 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

VIGNALI, CRISTIAN;RANALLI, PIERO;VITO, FABIO;
2012

Abstract

We present results on a search of heavily obscured active galaxies z > 1.7 using the rest-frame 9-20 keV excess for X-ray sources detected in the deep XMM-CDFS survey. Out of 176 sources selected with the conservative detection criteria (>8σ) in the first source catalogue of Ranalli et al. (in prep.), 46 objects lie in the redshift range of interest with the median redshift ˜ z≃ 2.5 ≃ 2.5. Their typical rest-frame 10-20 keV luminosity is 1044 erg s-1, as observed. Among optically faint objects that lack spectroscopic redshift, four were found to be strongly absorbed X-ray sources, and the enhanced Fe K emission or absorption features in their X-ray spectra were used to obtain X-ray spectroscopic redshifts. Using the X-ray colour-colour diagram based on the rest-frame 3-5 keV, 5-9 keV, and 9-20 keV bands, seven objects were selected for their 9-20 keV excess and were found to be strongly absorbed X-ray sources with column density of NH ≥ 0.6 × 10^24 cm-2, including two possible Compton thick sources. While they are emitting at quasar luminosity, ~3/4 of the sample objects are found to be absorbed by NH > 10^22 cm-2. A comparison with local AGN at the matched luminosity suggests an increasing trend of the absorbed source fraction for high-luminosity AGN towards high redshifts.
2012
Iwasawa K.; Gilli R.; Vignali C.; Comastri A.; Brandt W.N.; Ranalli P.; Vito F.; Cappelluti N.; Carrera F.J.; Falocco S.; Georgantopoulos I.; Mainieri V.; Paolillo M.
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Utilizza questo identificativo per citare o creare un link a questo documento: https://hdl.handle.net/11585/126451
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