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The XMM Newton/2dF Survey - IV. The X-ray spectral properties of the hard sources

By I. Georgantopoulos, A. Georgakakis, A. Akylas, G. C. Stewart, O. Giannakis, T. Shanks and S. Kitsionas

Abstract

We present an analysis of the X-ray spectral properties of 61 hard X-ray-selected (2–8 keV) sources from the bright (f2–8keV > 10−14 erg cm−2 s−1)XMM–Newton/2dF survey. This comprises nine XMM–Newton pointings in the North Galactic Pole region (∼1.6 deg2) and overlaps with the SDSS, 2QZ and 2dFGRS surveys. Our sources contribute about 50 per cent of the 2–10 keV X-ray background down to the flux limit of 10−14 erg cm−2 s−1. The hardness ratio distribution of the sample suggests a deficit of heavily absorbed sources. A spectral fit to the coadded total source spectrum yields a steep photon index, Γ= 1.83+0.04−0.05. All but eight sources have optical counterparts down to the SDSS photometric limit of r≈ 22.5. Spectroscopic identifications exist for 34 sources. The vast majority (24 sources) are associated with broad-line (BL) active galactic nuclei (AGN), while only seven present narrow or no emission lines. Five sources are probably associated with Galactic stars. Finally, we present photometric redshifts for another 17 probable AGN. The combined spectrum of the 24 spectroscopically identified BL AGN is steep (Γ= 2.02+0.04−0.05), while that of the seven AGN that do not present broad lines is flatter, with Γ= 1.64+0.11−0.11. The spectrum of the eight optically unidentified sources is flat with Γ≈ 1.1. Spectral fits to the individual BL AGN reveal large absorption (rest-frame column density >1022 cm−2) in only two cases. The individual spectra of the narrow-line AGN present significant evidence for even a moderate absorption (3 × 1021 cm−2) in only one case

Topics: galaxies: active, quasars: general, X-rays: general
Publisher: Oxford University Press (OUP), Royal Astronomical Society
Year: 2004
DOI identifier: 10.1111/j.1365-2966.2004.07899.x
OAI identifier: oai:lra.le.ac.uk:2381/798

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