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Issue A&A
Volume 457, Number 2, October II 2006
Page(s) 393 - 404
Section Cosmology (including clusters of galaxies)
DOI http://dx.doi.org/10.1051/0004-6361:20065284



A&A 457, 393-404 (2006)
DOI: 10.1051/0004-6361:20065284

The XMM large scale structure survey: properties and two-point angular correlations of point-like sources

P. Gandhi1, 2, O. Garcet3, L. Disseau4, 2, F. Pacaud5, M. Pierre5, A. Gueguen5, D. Alloin5, 2, L. Chiappetti6, E. Gosset3, D. Maccagni6, J. Surdej3 and I. Valtchanov7

1  Institute of Astronomy, Madingley Road, University of Cambridge, CB3 0HA, UK
    e-mail: pg@ast.cam.ac.uk
2  European Southern Observatory, Casilla 19001, Santiago, Chile
3  Institut d'Astrophysique et de Géophysique, Université de Liège, Belgium
4  École Normale Supérieure, Paris, France
5  CEA/DSM/DAPNIA, Service d'Astrophysique, Saclay, 91191 Gif-sur-Yvette, France
6  INAF IASF Milano, via Bassini 15, 20133 Milano, Italy
7  Astrophysics group, Blackett Laboratory, Imperial College, London, UK

(Received 27 March 2006 / Accepted 6 July 2006 )

Abstract
We analyze X-ray sources detected over 4.2 pseudo-contiguous sq. deg. in the 0.5-2 keV and 2-10 keV bands down to fluxes of $2\times 10^{-15}$ and $8\times 10^{-15}$ erg s-1 cm-2 respectively, as part of the XMM-Newton Large Scale Structure Survey. The log N-log S in both bands shows a steep slope at bright fluxes, but agrees well with other determinations below ~ $2 \times 10^{-14}$ erg s-1 cm-2. The detected sources resolve close to 30 per cent of the X-ray background in the 2-10 keV band. We study the two-point angular clustering of point sources using nearest neighbours and correlation function statistics and find a weak, positive signal for ~1130 sources in the 0.5-2 keV band, but no correlation for ~400 sources in the 2-10 keV band below scales of 100 arcsec. A sub-sample of ~200 faint sources with hard X-ray count ratios, that is likely to be dominated by obscured AGN, does show a positive signal with the data allowing for a large angular correlation length, but only at the ~2 (3)$\sigma$ level, based on re-sampling (Poisson) statistics. We discuss possible implications and emphasize the importance of wider, complete surveys in order to fully understand the large scale structure of the X-ray sky.


Key words: X-rays: diffuse background -- large-scale structure of Universe -- galaxies: Seyfert



© ESO 2006


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