The XMM-Newton serendipitous survey. IV. Optical identification of the XMM-Newton medium sensitivity survey (XMS)

Barcons, X.; Carrera, F.J.; Ceballos, M.T.; Page, M.J.; Bussons-Gordo, J.; Corral, A.; Ebrero, J.; Mateos, S.; Tedds, J.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.; Pérez-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.; Ullán, A.; Ward, M.J.; Warwick, R.S.; Wheatley, P.J.; Webb, N.A.; Worrall, D.; Yuan, W.; Ziaeepour, H.

Abstract

Aims.X-ray sources at intermediate fluxes (a few 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.

Citation

Barcons, X., Carrera, F., Ceballos, M., Page, M., Bussons-Gordo, J., Corral, A., …Ziaeepour, H. (2007). The XMM-Newton serendipitous survey. IV. Optical identification of the XMM-Newton medium sensitivity survey (XMS). Astronomy & Astrophysics, 476(3), 1191-1203. https://doi.org/10.1051/0004-6361%3A20077606

• Journal Article Type: Article
• Publication Date: Dec 1, 2007
• Deposit Date: Feb 20, 2014
• Publicly Available Date: Feb 21, 2014
• Journal: Astronomy and astrophysics.
• Print ISSN: 0004-6361
• Electronic ISSN: 1432-0746
• Publisher: EDP Sciences
• Peer Reviewed: Peer Reviewed
• Volume: 476
• Issue: 3
• Pages: 1191-1203
• DOI: https://doi.org/10.1051/0004-6361%3A20077606
• Keywords: X-rays, Galaxies, Stars.
• Public URL: https://durham-repository.worktribe.com/output/1564961