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Title:
Revisiting the baryon fractions of galaxy clusters: a comparison with WMAP 3-yr results
Authors:
McCarthy, I. G.; Bower, R. G.; Balogh, M. L.
Affiliation:
AA(Department of Physics, University of Durham, South Road, Durham DH1 3LE), AB(Department of Physics, University of Durham, South Road, Durham DH1 3LE), AC(Department of Physics and Astronomy, University of Waterloo, Waterloo, ON, Canada N2L 3G1)
Publication:
Monthly Notices of the Royal Astronomical Society, Volume 377, Issue 4, pp. 1457-1463. (MNRAS Homepage)
Publication Date:
06/2007
Origin:
MNRAS
MNRAS Keywords:
galaxies: clusters: general, cosmology: theory, X-rays: galaxies: clusters
DOI:
10.1111/j.1365-2966.2007.11733.x
Bibliographic Code:
2007MNRAS.377.1457M

Abstract

The universal baryonic mass fraction (Ωb/Ωm) can be sensitively constrained using X-ray observations of galaxy clusters. In this paper, we compare the baryonic mass fraction inferred from measurements of the cosmic microwave background with the gas mass fractions (fgas) of a large sample of clusters taken from the recent literature. In systems cooler than 4 keV, fgas declines as the system temperature decreases. However, in higher temperature systems, fgas(r500) converges to ~(0.12 +/- 0.02)(h/0.72)-1.5, where the uncertainty reflects the systematic variations between clusters at r500. This is significantly lower than the maximum-likelihood value of the baryon fraction from the recently released Wilkinson Microwave Anisotropy Probe (WMAP) 3-yr results. We investigate possible reasons for this discrepancy, including the effects of radiative cooling and non-gravitational heating, and conclude that the most likely solution is that Ωm is higher than the best-fitting WMAP value (we find Ωm = 0.36+0.11-0.08), but consistent at the 2σ level. Degeneracies within the WMAP data require that σ8 must also be greater than the maximum likelihood value for consistency between the data sets.
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