Article
Cosmological constraints from the Xray gas mass fraction in relaxed lensing clusters observed with Chandra
University of Cambridge, Cambridge, England, United Kingdom
Monthly Notices of the Royal Astronomical Society (Impact Factor: 5.11). 05/2002; 334(2). DOI: 10.1046/j.13658711.2002.05601.x Source: arXiv
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 "The observed Xray gas mass fraction profiles in the clusters with the radial axis scaled in units of r2500 (Allen et al . 2002b"
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ABSTRACT: Chandra observations of rich, relaxed galaxy clusters allow the properties of the Xray gas and the total gravitating mass to be determined precisely. Here, we present results for a sample of the most Xray luminous, dynamically relaxed clusters known. We show that the Chandra data and independent gravitational lensing studies provide consistent answers on the mass distributions in the clusters. The mass profiles exhibit a form in good agreement with the predictions from numerical simulations. Combining Chandra results on the Xray gas mass fractions in the clusters with independent measurements of the Hubble constant and the mean baryonic matter density in the Universe, we obtain a tight constraint on the mean total matter density of the Universe, Omega(m), and an interesting constraint on the cosmological constant, Omega(Lambda). We also describe the 'virial relations' linking the masses, Xray temperatures and luminosities of galaxy clusters. These relations provide a key step in linking the observed number density and spatial distribution of clusters to the predictions from cosmological models. The Chandra data confirm the presence of a systematic offset of ca. 40% between the normalization of the observed masstemperature relation and the predictions from standard simulations. This finding leads to a significant revision of the bestfit value of sigma(8) inferred from the observed temperature and luminosity functions of clusters.  [Show abstract] [Hide abstract]
ABSTRACT: Dissertation & Ph. D. thesis  [Show abstract] [Hide abstract]
ABSTRACT: We use a generalized procedure for the combined likelihood analysis of different cosmological probes, the ‘hyperparameters’ method, that allows freedom in the relative weights of the raw measurements. We perform a joint analysis of the Cepheidcalibrated data from the Hubble Space Telescope Key Project and the baryon mass fraction in clusters to constrain the total matter density of the Universe, Ωm, and the Hubble parameter, h. We compare the results obtained using the hyperparameters method with the estimates from standard χ2 analysis. We assume that the Universe is spatially flat, with a cosmological constant. We adopt the big bang nucleosynthesis constraint for the baryon density, assuming the uncertainty is Gaussian distributed. Using this and the cluster baryon fraction data, we find that the matter density and the Hubble constant are correlated, Ωmh0.5≈ 0.25, with preference for a very high h. To break the degeneracy, we add in the Cepheidcalibrated data and find the bestfitting values (Ωm, h) = (0.26+0.06−0.06, 0.72+0.04−0.02) (68 per cent confidence limits) using the hyperparameters approach. We use the derived hyperparameters to ‘grade’ the six different data sets we analyse. Although our analysis is free of assumptions about the power spectrum of fluctuations, our results are in agreement with the Λ cold dark matter ‘concordance’ parameters derived from the cosmic microwave background anisotropies combined with Type Ia supernovae, redshift surveys and other probes.