Cosmological Implications of Galaxy Cluster Evolution and Substructure

We examined the sensitivity of the spatial morphologies of galaxy clusters, as observed in X-rays, to the cosmological parameters Ω m,0, Ω Λ , and σ 8 (rms mass fluctuations in a sphere of radius 8h-1 Mpc). Morphologies of galaxy clusters provide constraints on the dynamical state of these systems. We observed sources in a flux-limited sample of 50 nearby (i.e. 0.015≤{z}≤0.2) galaxy clusters with ROSAT and compared these with results from high-resolution N-body simulations incorporating TREESPH gas hydrodynamics. The observational sample was derived from the HIFLUGCS sample of Reiprich and Böhringer (2002) and has a lower X-ray flux limit in the 0.1-2.4 keV band of 2.0× 10-11 erg s-1 cm-2 to ensure we are in the cluster regime. Variants of the standard cold dark matter (CDM) models are considered having different spatial curvatures and normalizations: SCDM (Ω m,0 = 1, Ω Λ =0, σ 8=1), OCDM (Ω m,0 = 0.3, Ω Λ =0, σ 8=0.85), LCDM07 (Ω m,0 = 0.3, Ω Λ =0.7, σ 8=0.7) and LCDM09 (Ω m,0 = 0.3, Ω Λ =0.7, σ 8=0.9). Cluster X-ray morphologies are quantified using the power ratios (PRm) of Buote and Tsai (1996). We compared the observations and simulations at an aperture of 0.5h70-1 Mpc. The LCDM07 model, with σ 8=0.7, is indistinguishable from the SCDM model. The comparisons with observations disfavor OCDM as opposed to LCDM07 and SCDM. This indicates Ω m,0}+Ω {Λ =1, independently of the WMAP (2003) first CMB results.