The baryon fraction in X-Rays galaxy clusters revisited
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One of the most direct way to constrain the matter density of the universe $Ω_M$ is to measure the baryon content in X-Rays clusters of galaxies. Typical value of the mean gas mass fraction is $\fg \sim 0.15h^{-3/2}$ which leads to $\omM <0.4$. In this talk I will discuss the issue of the gas fraction radial distribution inside a cluster and foccus on the apparent discrepancy between the theoretical shape predicted by numerical simulations and the observations. I will show that a significant part of this discrepancy is due to several systematics in both the gas mass and total mass determinations. Revising the gas as well as the binding masses removes such a discrepancy and results in a lower baryon mass fraction of $\fb(r_{500}) \sim 10 %$ (Sadat & Blanchard 2001). Finally, I will discuss the cosmological constraints we obtain when we combine the revised baryon fraction with primordial fluctuations.
9 pages, 5 figures, talk given at COSMO-01 Workshop, Rovaniemi, Finland, August 30 - September 4, 2001 Slight revision to Fig. 3 caption
9 pages, 5 figures, talk given at COSMO-01 Workshop, Rovaniemi, Finland, August 30 - September 4, 2001 Slight revision to Fig. 3 caption