The XMM-LSS survey. Survey design and first results**Paper based on observations obtained with the XMM,CFH, ESO (Prg: P70. A-0283; .A-0733),VLA, CTIO and Las Campanas observatories.

Abstract

The XMM Large Scale Structure survey (XMM-LSS) is a medium deep largearea X-ray survey. Its goal is to extend large scale structure investigationsattempted using ROSAT cluster samples to two redshift bins between0<z<1 while maintaining the precision of earlier studies. Two main goals have constrained thesurvey design: the evolutionary study of the cluster–cluster correlation function and of thecluster number density. The adopted observing configuration consists of an equatorialmosaic of 10 ks pointings, separated by and covering 8° × 8°, giving a pointsource sensitivity of in the 0.5–2 keV band. This will yield more than 800 clusters ofgalaxies and a sample of X-ray AGN with a space density of about300 deg−2. We present the expected cosmological implications of the survey in the context ofΛCDM models and cluster evolution. We give an overview of the first observational results.The XMM-LSS survey is associated with several other major surveys, ranging from the UVto the radio wavebands, which will provide the necessary resources for X-ray sourceidentification and further statistical studies. In particular, the associated CFHTLS weaklensing and AMiBA Sunyaev–Zel’dovich surveys over the entire XMM-LSS area willprovide for the first time a comprehensive study of the mass distribution and of clusterphysics in the universe on scales of a few hundred Mpc. We describe the maincharacteristics of our wavelet-based X-ray pipeline and source identification procedures,including the classification of the cluster candidates by means of a photometricredshift analysis. This permits the selection of suitable targets for spectroscopicfollow-up. We present preliminary results from the first 25 XMM-LSS pointings: X-raysource properties, optical counterparts, and highlights from the first Magellan andVLT/FORS2 spectroscopic runs as well as preliminary results from the NIR search forz>1 clusters.The results are promising and, so far, in accordance with our predictions. In particular: (1) we reproducethe logN–logS distributionfor point sources obtained from deeper surveys at our sensitivity; (2) we find a cluster number density of15–20 deg−2; (3) for the first time, we statistically sample the group mass regime at a redshift out to.