The XMM-Newton $\\Omega$ Project
Résumé
The abundance of high-redshift galaxy clusters depends sensitively on the matter density $\\OmM$ and, to a lesser extent, on the cosmological constant $\\Lambda$. Measurements of this abundance therefore constrain these fundamental cosmological parameters, and in a manner independent and complementary to other methods, such as observations of the cosmic microwave background and distance measurements. Cluster abundance is best measured by the X-ray temperature function, as opposed to luminosity, because temperature and mass are tightly correlated, as demonstrated by numerical simulations. Taking advantage of the sensitivity of XMM-Newton, our Guaranteed Time program aims at measuring the temperature of the highest redshift (z>0.4) SHARC clusters, with the ultimate goal of constraining both $\\OmM$ and $\\Lambda$.