The XMM/Megacam-VST/VIRMOS Large-Scale Structure Survey

Abstract

Abstract. The objective of the XMM-LSS Survey is to map the large scale structure of the universe, as highlighted by clusters and groups of galaxies, out to a redshift of about 1, over a single 8 × 8 sq.deg. area. For the first time, this will reveal the topology of the distribution of the deep potential wells and provide statistical measurements at truly cosmological distances. In addition, clusters identified via their X-ray properties will form the basis for the first uniformly-selected, multi-wavelength survey of the evolution of clusters and individual cluster galaxies as a function of redshift. The survey will also address the very important question of the QSO distribution within the cosmic web. ContextAs the largest gravitationally bound entities, clusters of galaxies play a key role in our understanding of the universe. In particular, the redshift evolution of both their individual properties and global space distribution are essential to constrain cosmological scenarios. Since clusters originate from high amplitude initial density fluctuations, they are rare events and dedicated search programmes are necessary to provide homogeneous samples suitable for statistical studies (the mean cluster/group number density 1 is of the order 5 10 −6 Mpc −3 [1]). A notable sample is the Abell (ACO) catalogue [2] which enabled the first measurement of the local cluster power spectrum [3]. Optical catalogues are, however, severely hampered by projection effects and galaxy density contrasts with respect to the background become marginal beyond z ∼ 1, unless detailed multi-color information is available, together with sophisticated detection algorithms. In this context, the X-ray wave-band represents much more than a useful alternative: it is a secure and straightforward approach. A high latitude galactic field observed at medium sensitivity (∼ 10 14 erg/s/cm 2 ) shows basically two types of objects: QSO (pointlike) and clusters (extended), the cluster X-ray emission being due to the hot diffuse gas trapped in the cluster potential. Moreover, the X-ray temperature and luminosity can be related to the cluster total mass, provided the physics of the 1 We assume Ho = 50 km/s/Mpc and qo = 0.5 throughout this paper

A Test of Photometric Redshifts for X‐Ray–selected Sources

“…1 There are strong practical motivations for using an expanded sample of X-ray selected sources to assess the reliability of photometric redshifts for these objects. Foremost, an efficient means of redshift estimation is required to maximize the return from large area Chandra and XMM-Newton surveys, such as the Lockman Hole survey (Chandra, PI: Barger), the Chandra Multiwavelength Project (ChaMP Wilkes et al 2000), the XMM-LSS survey (Pierre et al 2001), and the upcoming Chandra survey in the NOAO Deep-Wide Field (9 sq. degrees, PIs: Jones & Murray).…”