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

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 and 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 ~ 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)σ 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.