VST-OAC survey of the XMM Large Scale Structure Survey

Responsible in OAC: S. Andreon, M. Capaccioli

Team members in OAC: G. Busarello, G. Longo, P. Merluzzi, M. Radovich, A. Rifatto, A. Marino, A. Grado, D. de Martino, M. Arnaboldi, J. Alcalà, E. Covino, M. Marconi, V. Ripepi, E. Puddu

External collaborators: F. Caputo and R. Scaramella (Mt.Porzio Astron. Obs., Rome, Italy), G. Theureau (Paris-Meudon Obs., France), P. Rafanelli (Padua Univ., Italy), R. de Ritis, C. Rubano, P. Scudellaro (Naples Univ., Italy), V. Castellani (Pisa Univ., Italy)

The study of the Large Scale Structure (LSS) of the Universe has undergone spectacular developments within the last 15 years in all research areas. On the theoretical front the "cosmic web" paradigm (Bond et al. 1996) reconciles the (Russian) pancaking and (Western) hierarchical clustering pictures. Extensive numerical N-body simulations demonstrate the formation of a large-scale filamentary network whose topology, scales and evolution rate are strong functions of both the assumed cosmological model and the initial fluctuation spectrum.

The XMM-LSS consortium, which includes OAC, has the observational goal of mapping the distribution of matter over a 8 x 8 deg2 area out to a redshift ~1 using three complementary techniques: (1) X-ray observations to locate galaxy clusters and QSOs; (2) optical observations to obtain the galaxy distribution and to locate dark matter through a weak lensing analysis; and (3) Sunyaev-Zel'dovich effect observations to measure the distribution of diffuse extragalactic hot gas. The unrivaled sensitivity and good point-spread function of XMM will open a new era for X-ray large-scale structure studies:more than 500 times as sensitive as REFLEX survey the largest cluster survey over a single area to date (Böhringer et al 1998). The XMM-LSS survey proposed by the XMM-LSS consortium, and recently approved by XMM TAC, is designed to probe the large scale distribution of clusters of galaxies out to z ~ 1 and of QSOs much further out. This will provide unprecedented insight onto LSS formation and, thus, cosmology. The consortium will therefore be able to probe the nature and amount of dark matter, the initial fluctuation spectrum and other fundamental cosmological parameters.

OAC is heavily involved in the XMM-LSS consortium and, furthermore, has its own scientific interests which will great benefit of the availability of the XMM-LSS consortium data. This prompted the OAC Director to allocate several guaranteed VST nights to perform the optical follow up on the same regione covered by the XMM-LSS consortium. This survey takes the name of VST-OAC Survey of the XMM-LSS field, and will cover 64 square degrees in two bands (V and v narrow) and 10° in four bands (V, v narrow, R and z930). The survey will require 56 VST nights.

The VST-OAC survey is aimed at sampling equal volumes of the universe at the same rest-frame wavelength and depth. It will address many relevant topics. The OAC researchers and their collaborators are mainly interested in the following scientific goals:

Status of the project

The project started in the early 1999. We have completed a simplified feasibility study and we are currently addressing the problem of the data reduction and analysis through a pilot survey conducted with the 8k´ 8k camera at the ESO 2.2m telescope, and through the scientific use of the 12k´ 8k images taken at the Canada-France-Hawaii telescope.

Novel artificial intelligence algorithms for source detection and classification (star/galaxies) have been developed (see NExt; Sect. 9.6.5) and we are capitalizing on the experience gained in analyzing the WF DPOSS-II plates (CRoNaRio project, Sect. 8.4).

The first observations of the VST-OAC survey of the XMM-Large Scale Structure Survey are planned for the end of 2001 (see also this URL )