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Date and Time of the Query: 2019-04-19 T07:14:48 PDT
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For refcode 2008MNRAS.383..879A:
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Copyright by Royal Astronomical Society. 2008MNRAS.383..879A Improved constraints on dark energy from Chandra X-ray observations of the largest relaxed galaxy clusters S. W. Allen, D. A. Rapetti, R. W. Schmidt, H. Ebeling, R. G. Morris and A. C. Fabian Abstract. We present constraints on the mean matter density, {OMEGA}_m_, dark energy density, {OMEGA}_DE_, and the dark energy equation of state parameter, w, using Chandra measurements of the X-ray gas mass fraction (f_gas_) in 42 hot (kT > 5 keV), X-ray luminous, dynamically relaxed galaxy clusters spanning the redshift range 0.05 < z < 1.1. Using only the f_gas_ data for the six lowest redshift clusters at z < 0.15, for which dark energy has a negligible effect on the measurements, we measure {OMEGA}_m_ = 0.28 +/- 0.06 (68 per cent confidence limits, using standard priors on the Hubble constant, H_0_, and mean baryon density, {OMEGA}_b_ h^2^). Analysing the data for all 42 clusters, employing only weak priors on H_0_ and {OMEGA}_b_ h^2^, we obtain a similar result on {OMEGA}_m_ and a detection of the effects of dark energy on the distances to the clusters at ~99.99 per cent confidence, with {OMEGA}_DE_ = 0.86 +/- 0.21 for a non-flat {LAMBDA}CDM model. The detection of dark energy is comparable in significance to recent type Ia supernovae (SNIa) studies and represents strong, independent evidence for cosmic acceleration. Systematic scatter remains undetected in the f_gas_ data, despite a weighted mean statistical scatter in the distance measurements of only ~5 per cent. For a flat cosmology with a constant dark energy equation of state, we measure {OMEGA}_m_ = 0.28 +/- 0.06 and w = -1.14 +/- 0.31. Combining the f_gas_ data with independent constraints from cosmic microwave background and SNIa studies removes the need for priors on {OMEGA}_b_ h^2^ and H_0_ and leads to tighter constraints: {OMEGA}_m_ = 0.253 +/- 0.021 and w = -0.98 +/- 0.07 for the same constant-w model. Our most general analysis allows the equation of state to evolve with redshift. Marginalizing over possible transition redshifts 0.05 < z_t_ < 1, the combined f_gas_ + CMB + SNIa data set constrains the dark energy equation of state at late and early times to be w_0_ = -1.05 +/- 0.29 and w_et_ = -0.83 +/- 0.46, respectively, in agreement with the cosmological constant paradigm. Relaxing the assumption of flatness weakens the constraints on the equation of state by only a factor of ~2. Our analysis includes conservative allowances for systematic uncertainties associated with instrument calibration, cluster physics and data modelling. The measured small systematic scatter, tight constraint on {OMEGA}_m_ and powerful constraints on dark energy from the f_gas_ data bode well for future dark energy studies using the next generation of powerful X-ray observatories, such as Constellation-X. Key words: cosmic microwave background, cosmological parameters, cosmology: observations, dark matter, distance scale, X-rays: galaxies: clusters
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