Cosmology and Astrophysics from Relaxed Galaxy Clusters II: Cosmological Constraints

Adam B. Mantz; Steven W. Allen; R. Glenn Morris; David A. Rapetti; Douglas E. Applegate; Patrick L. Kelly; Anja von der Linden; Robert W. Schmidt

doi:10.1093/mnras/stu368

paper

Cosmology and Astrophysics from Relaxed Galaxy Clusters II: Cosmological Constraints

arXiv:1402.6212 · doi:10.1093/mnras/stu368

Abstract

We present cosmological constraints from measurements of the gas mass fraction, $f_{g a s}$ , for massive, dynamically relaxed galaxy clusters. Our data set consists of Chandra observations of 40 such clusters, identified in a comprehensive search of the Chandra archive, as well as high-quality weak gravitational lensing data for a subset of these clusters. Incorporating a robust gravitational lensing calibration of the X-ray mass estimates, and restricting our measurements to the most self-similar and accurately measured regions of clusters, significantly reduces systematic uncertainties compared to previous work. Our data for the first time constrain the intrinsic scatter in $f_{g a s}$ , $(7.4 \pm 2.3)$ % in a spherical shell at radii 0.8-1.2 $r_{2500}$ , consistent with the expected variation in gas depletion and non-thermal pressure for relaxed clusters. From the lowest-redshift data in our sample we obtain a constraint on a combination of the Hubble parameter and cosmic baryon fraction, $h^{3/2} Ω_{b} / Ω_{m} = 0.089 \pm 0.012$ , that is insensitive to the nature of dark energy. Combined with standard priors on $h$ and $Ω_{b} h^{2}$ , this provides a tight constraint on the cosmic matter density, $Ω_{m} = 0.27 \pm 0.04$ , which is similarly insensitive to dark energy. Using the entire cluster sample, extending to $z > 1$ , we obtain consistent results for $Ω_{m}$ and interesting constraints on dark energy: $Ω_{Λ} = 0.6 5_{- 0.22}^{+ 0.17}$ for non-flat $Λ$ CDM models, and $w = - 0.98 \pm 0.26$ for flat constant- $w$ models. Our results are both competitive and consistent with those from recent CMB, SNIa and BAO data. We present constraints on models of evolving dark energy from the combination of $f_{g a s}$ data with these external data sets, and comment on the possibilities for improved $f_{g a s}$ constraints using current and next-generation X-ray observatories and lensing data. (Abridged)

25 pages, 14 figures, 8 tables. Accepted by MNRAS. Code and data can be downloaded from http://www.slac.stanford.edu/~amantz/work/fgas14/ . v2: minor fix to table 1, updated bibliography

Cosmology and Astrophysics from Relaxed Galaxy Clusters II: Cosmological Constraints

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