2012A&A...546A..84I -
Astronomy and Astrophysics, volume 546A, 84-84 (2012/10-1)
The XMM deep survey in the CDF-S. II. A 9-20 keV selection of heavily obscured active galaxies at z > 1.7.
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. and PAOLILLO M.
Abstract (from CDS):
We present results on a search of heavily obscured active galaxies z>1.7 using the rest-frame 9-20keV 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. Their typical rest-frame 10-20keV luminosity is 1044erg/s, 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 3-5keV, 5-9keV, and 9-20keV bands, seven objects were selected for their 9-20keV excess and were found to be strongly absorbed X-ray sources with column density of NH≥0.6x1024cm–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>1022cm–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.
Abstract Copyright:
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Journal keyword(s):
galaxies: active - X-rays: galaxies
Simbad objects:
53
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