Cosmological constraints from the X-ray gas mass fraction in relaxed lensing clusters observed with Chandra

Monthly Notices of the Royal Astronomical Society (Impact Factor: 5.23). 05/2002; 334(2). DOI: 10.1046/j.1365-8711.2002.05601.x
Source: arXiv

ABSTRACT We present precise measurements of the X-ray gas mass fraction for a sample of luminous, relatively relaxed clusters of galaxies observed with the Chandra Observatory, for which independent confirmation of the mass results is available from gravitational lensing studies. Parameterizing the total (luminous plus dark matter) mass profiles using the model of Navarro, Frenk & White (1997), we show that the X-ray gas mass fractions in the clusters asymptote towards an approximately constant value at a radius r_2500, where the mean interior density is 2500 times the critical density of the Universe at the redshifts of the clusters. Combining the Chandra results on the X-ray gas mass fraction and its apparent redshift dependence with recent measurements of the mean baryonic matter density in the Universe and the Hubble Constant determined from the Hubble Key Project, we obtain a tight constraint on the mean total matter density of the Universe, Omega_m = 0.30^{+0.04}_{-0.03}, and measure a positive cosmological constant, Omega_Lambda = 0.95^{+0.48}_{-0.72}. Our results are in good agreement with recent, independent findings based on analyses of anisotropies in the cosmic microwave background radiation, the properties of distant supernovae, and the large-scale distribution of galaxies. Comment: Accepted for publication in MNRAS Letters (6 pages, 3 figures)

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    • "The observed X-ray 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 X-ray gas and the total gravitating mass to be determined precisely. Here, we present results for a sample of the most X-ray 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 X-ray 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, X-ray 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 mass-temperature relation and the predictions from standard simulations. This finding leads to a significant revision of the best-fit value of sigma(8) inferred from the observed temperature and luminosity functions of clusters.
    Philosophical Transactions of The Royal Society A Mathematical Physical and Engineering Sciences 10/2002; 360(1798):2005-17. DOI:10.1098/rsta.2002.1056 · 2.86 Impact Factor
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    ABSTRACT: Dissertation & Ph. D. thesis
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    ABSTRACT: We use a generalised procedure for the combined likelihood analysis of different cosmological probes, the `Hyper-Parameters' method, that allows freedom in the relative weights of the raw measurements. We perform a joint analysis of the cepheid-calibrated data from the Hubble Space Telescope Key Project and the baryon mass fraction in clusters to constrain the total matter density of the universe, Omega_m, and the Hubble parameter, h. We compare the results obtained using Hyper-Parameters method with the estimates from standard chi^2 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, Omega_m h^0.5~0.25, with preference for a very high h. To break the degeneracy, we add in the cepheid-calibrated data and find the best fit values (Omega_m, h) = (0.26 (+0.06,-0.06),0.72 (+0.04,-0.02)) (68 per cent confindence limits) using the Hyper-Parameters approach. We use the derived Hyper-Parameters to `grade' the 6 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 Lambda-Cold Dark Matter `concordance' parameters derived from the Cosmic Microwave Background anisotropies combined with Supernovae Ia, redshift surveys and other probes. Comment: 7 pages, 5 figures, revised to match the accepted MNRAS version
    Monthly Notices of the Royal Astronomical Society 02/2002; 340(2). DOI:10.1046/j.1365-8711.2003.06313.x · 5.23 Impact Factor
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