Revisiting the baryon fractions of galaxy clusters: a comparison with WMAP 3-yr results |
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Authors: | I G McCarthy R G Bower M L Balogh |
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Institution: | Department of Physics, University of Durham, South Road, Durham DH1 3LE;Department of Physics and Astronomy, University of Waterloo, Waterloo, ON, Canada N2L 3G1 |
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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 ( f gas) of a large sample of clusters taken from the recent literature. In systems cooler than 4 keV, f gas declines as the system temperature decreases. However, in higher temperature systems, f gas( r 500) converges to ≈(0.12 ± 0.02)( h /0.72)−1.5 , where the uncertainty reflects the systematic variations between clusters at r 500. 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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Keywords: | galaxies: clusters: general cosmology: theory X-rays: galaxies: clusters |
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