Cluster Morphologies as a Test of Different Cosmological Models

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We investigate how cluster morphology is affected by the cosmological constant in low-density universes. Using high-resolution cosmological N-body/SPH simulations of flat (Ω₀ = 0.3, λ₀ = 0.7, ΛCDM) and open (Ω₀ = 0.3, λ₀ = 0, OCDM) cold dark matter universes, we calculate statistical indicators to quantify the irregularity of the cluster morphologies. We study axial ratios, center shifts, cluster clumpiness, and multipole moment power ratios as indicators for the simulated clusters at z=0 and 0.5. Some of these indicators are calculated for both the X-ray surface brightness and projected mass distributions. In ΛCDM all these indicators tend to be larger than those in OCDM at z=0. This result is consistent with the analytical prediction of Richstone, Loeb, & Turner, that is, clusters in ΛCDM are formed later than in OCDM, and have more substructure at z=0. We make a Kolmogorov-Smirnov test on each indicator for these two models. We then find that the results for the multipole moment power ratios and the center shifts for the X-ray surface brightness are under the significance level (5%). We results also show that these two cosmological models can be distinguished more clearly at z=0 than z = 0.5 by these indicators.