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Title: The XMM-Newton serendipitous survey - IV. Optical identification of the XMM-Newton medium sensitivity survey (XMS)
Authors: Barcons, X.
Carrera, F. J.
Ceballos, M. T.
Page, M. J.
Bussons-Gordo, J.
Corral, A.
Ebrero, J.
Mateos, S.
Tedds, Jonathan A.
Watson, M. G.
Baskill, D.
Birkinshaw, M.
Boller, T.
Borisov, N.
Bremer, M.
Bromage, G. E.
Brunner, H.
Caccianiga, A.
Crawford, C. S.
Cropper, M. S.
Della Ceca R
Derry, P.
Fabian, A. C.
Guillout, P.
Hashimoto, Y.
Hasinger, G.
Hassall, B. J. M.
Lamer, G.
Loaring, N. S.
Maccacaro, T.
Mason, K. O.
McMahon, R. G.
Mirioni, L.
Mittaz, J. P. D.
Motch, C.
Negueruela, I.
Osborne, J. P.
Panessa, F.
Perez-Fournon, I.
Pye, J. P.
Roberts, T. P.
Rosen, S.
Schartel, N.
Schurch, N.
Schwope, A.
Severgnini, P.
Sharp, R.
Stewart, G. C.
Szokoly, G.
Ullan, A.
Ward, M. J.
Warwick, R. S.
Wheatley, P. J.
Webb, N. A.
Worrall, D.
Yuan, W.
Ziaeepour, H.
First Published: 1-Dec-2007
Publisher: EDP Sciences for European Southern Observatory (ESO)
Citation: Astronomy & Astrophysics, 2007, 476 (3), pp. 1191-U35
Abstract: Aims.X-ray sources at intermediate fluxes (a few $\times$ 10-14 erg cm-2 s-1) with a sky density of ~100 deg-2 are responsible for a significant fraction of the cosmic X-ray background at various energies below 10 keV. The aim of this paper is to provide an unbiased and quantitative description of the X-ray source population at these fluxes and in various X-ray energy bands. Methods.We present the XMM-Newton Medium sensitivity Survey (XMS), including a total of 318 X-ray sources found among the serendipitous content of 25 XMM-Newton target fields. The XMS comprises four largely overlapping source samples selected at soft (0.5-2 keV), intermediate (0.5-4.5 keV), hard (2-10 keV) and ultra-hard (4.5-7.5 keV) bands, the first three of them being flux-limited. Results.We report on the optical identification of the XMS samples, complete to 85-95%. At the flux levels sampled by the XMS we find that the X-ray sky is largely dominated by Active Galactic Nuclei. The fraction of stars in soft X-ray selected samples is below 10%, and only a few per cent for hard selected samples. We find that the fraction of optically obscured objects in the AGN population stays constant at around 15-20% for soft and intermediate band selected X-ray sources, over 2 decades of flux. The fraction of obscured objects amongst the AGN population is larger (~35-45%) in the hard or ultra-hard selected samples, and constant across a similarly wide flux range. The distribution in X-ray-to-optical flux ratio is a strong function of the selection band, with a larger fraction of sources with high values in hard selected samples. Sources with X-ray-to-optical flux ratios in excess of 10 are dominated by obscured AGN, but with a significant contribution from unobscured AGN.
DOI Link: 10.1051/0004-6361:20077606
ISSN: 0004-6361
Version: Publisher Version
Status: Peer-reviewed
Type: Journal Article
Rights: Copyright © 2007 ESO. Reproduced with permission from Astronomy & Astrophysics, © ESO.
Appears in Collections:Published Articles, Dept. of Physics and Astronomy

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