Testing General Relativity on Cosmic Scales with the Observed Abundance of Massive Clusters

摘要

Using observations of the growth of massive, X-ray flux-selected galaxy clusters, we ob-tain tight constraints on both the growth and expansion histories of the Universe. Our data set consists of 238 cluster detections from the ROSAT All-Sky Survey (RASS), and incor-porates follow-up observations of 94 of those clusters from the Chandra X-ray Observatory and/or ROSAT. Using a new statistical framework that self-consistently produces simulta-neous constraints on cosmology and X-ray scaling relations we account for survey biases, parameter degeneracies and the impact of systematic uncertainties to obtain improved con-straints on departures from General Relativity (GR) on cosmological scales. We parametrize the linear growth rate of cosmic structure with a power law of the mean matter density to the growth index, γ. Combining the X-ray cluster growth data with cluster gas-mass fraction (f_(gas)), Type Ia supernovae (SNIa), baryon acoustic oscillations (BAO), and cosmic microwave background (CMB) data, we find a tight correlation between γ and the normalization of the matter power spectrum, σ8. Allowing γ and the dark energy equation of state parameter, w, to take any constant values, we find no evidence for departures from the standard paradigm, GR+ACDM (cosmological constant plus cold dark matter). Our results highlight the power of X-ray cluster studies to constrain cosmology.