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Index - ... - The survey characteristics - Scientific Goals - Simulations (1/3) - ...

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The unrivaled sensitivity and good point-spread function of XMM will open a new era for X-ray large-scale structure studies.

Some 1000 times more sensitive than the REFLEX survey - the largest cluster survey over a single area to date (Böhringer et al 2001) - the XMM-LSS survey 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. We will be able to probe the nature and amount of dark matter, the initial fluctuation spectrum and other fundamental cosmological parameters.

cosmo1.eps.gz (gzipped Postscript, 6150 bytes)	cosmo2.eps.gz (gzipped Postscript, 5274 bytes)
Constraints upon the cosmological parameters m and 8 (the amplitude of mass fluctuations on 8 h-1 Mpc scale) for a CDM universe. Cluster abundance data provides strong constraints upon the m - 8 combination.	Constraints upon the cosmological parameters m and (the shape of the power spectrum) for a CDM universe. The correlation function is a powerful tool to constrain the shape of the initial spectrum.
Solid lines: XMM-LSS cluster counts - Dashed lines: correlation function. In each case, the 68%, 90% and 95% confidence level contours are shown along with the assumed model (cross). These calculations have been performed assuming that only the redshifts over the [0<z<1] x [64 deg2] volume are available. (Predictions from Refregier et al., 2001.)

In addition, identification of a "Coma-type" cluster within the XMM-LSS over the redshift range 1.5 < z < 2 has a probability of ~ 6.5 10^-7 in the current CDM scenario. Therefore, any such discoveries in the  survey would put the currently favoured cosmological model in great observational difficulty.

The primary science goals are:

• Map the large scale structures as outlined by clusters and groups of galaxies out to a redshift of 1. This will reveal the topology of the spatial distribution of deep potential wells at truly cosmological distances.
  
• Compute the correlation function of clusters of galaxies in two redshift bins 0 < z < 0.5, 0.5 < z < 1. This will be the first determination of the cluster correlation function at high z.
  
• Map the spatial distribution of AGN/QSO within the cosmic web as outlined by the cluster/group population. This will lead to a better understanding of the origin of AGN in terms of the initial density perturbation, galaxy interactions and will provide a window into the the effect of gravitational lensing on QSO properties.
  
• Compute the correlation function of QSO/AGN with a high degree of accuracy.
  
• Investigate the existence of X-ray bright (i.e. massive) clusters of galaxies between 1 < z < 2.
  
• Study the combined X-ray/optical evolutionary properties of clusters and QSO.
  
• Compare the cosmic web inferred from X-rays with the mass distribution determined by the galaxy distribution and the associated weak lensing survey in the optical. This will provide crucial information about bias mechanism as a function of redshift.
  
• With the associated Sunyaev-Zel'dovich survey, it will be possible to measure the Hubble constant at a much higher degree of accuracy and study in detail the low density, external part of clusters.
  
• The dense QSO X-ray population will provide a unique grid for further QSO absorption line studies and will allow a detailed investigation of the distribution, size and properties of absorbing intergalactic clouds.