Gas mass fraction from XMM-Newton and Chandra high redshift clusters and its use as a cosmological test

Laboratoire d'Astrophysique de Tarbes et Toulouse, OMP, CNRS, UMR 5572, UPS, 14 avenue E. Belin, 31400 Toulouse, France e-mail: [luis.ferramacho;alain.blanchard]@ast.obs-mip.fr

Received: 25 July 2006
Accepted: 29 September 2006

Abstract

Aims.We investigate the cosmological test based on the evolution of the gas fraction in X-ray galaxy clusters and the stability of the cosmological parameters derived from it.

Methods. Using a sample of distant clusters observed by XMM-Newton and Chandra, and comparing their gas fraction at different radii to the gas fraction observed for nearby clusters, we have determined the likelihood functions for in a flat universe and the confidence contours in the plane.

Results. Results obtained at the virial radius point to a high matter density Universe, while for inner radii the parameter obtained tends to decrease, reaching values compatible with the concordance model. The analysis allows us to conclude that this test provides ambiguous results due to the complex structure of the ICM that induces a dependence of the gas fraction on temperature, radius, and redshift, which cannot be accounted for by the self-similar picture expected from pure gravitational heating of the ICM.

Conclusions.The use of gas fraction in X-ray clusters to constrain cosmological parameters seems therefore to be compromised until a better understanding of the ICM physics and the ability to obtain observations of better quality up to the virial radius are achieved.