Sensitivity of galaxy cluster morphologies to Omega(0) and P(k)

We examine the sensitivity of the spatial morphologies of galaxy clusters to Omega(0) and P(k) using high-resolution N-body simulations with a large dynamic range. Variants of the standard cold dark matter (CDM) model are considered having different spatial curvatures, SCDM (Omega(0) = 1), OCDM (Omega(0) = 0.35), and LCDM (Omega(0) = 0.35, lambda(0) = 0.65) and different normalizations, sigma(8). We also explore critical density models with different spectral indices, n, of the scale-free power spectrum P (k) proportional to k(n). Cluster X-ray morphologies are quantified with power ratios (PRs), where we take for the X-ray emissivity j(gas) proportional to rho(DM)(2), which we argue is a suitable approximation for an analysis X-ray emissivity j(gas) proportional to rho(DM)(2), of PRs. We find that Omega(0) primarily influences the means of the PR distributions, whereas the power spectrum (n and sigma(8)) primarily affects their variances: log(10)(P-3/P-0) is the cleanest probe of Omega(0), since its mean is very sensitive to Omega(0) but very insensitive to P(k). The PR means easily distinguish the SCDM and OCDM models, while the SCDM and LCDM means show a more modest, but significant, difference (similar to 3 sigma). The OCDM and LCDM models are largely indistinguishable in terms of the PRs. Finally, we compare these models to a sample of ROSAT clusters and find that the PR means of the SCDM clusters exceed the ROSAT means with a high formal level of significance (similar to 4 sigma). Though the formal significance level of this rho(DM)(2)/X-ray comparison should be considered only approximate, we argue that taking into account the hydrodynamics and cooling will not reconcile a discrepancy this large. The PR means of the OCDM clusters are consistent, and the means of the LCDM clusters are marginally consistent, with those of the ROSAT clusters. Thus, we conclude that cluster morphologies strongly disfavour Omega = 1 CDM models while favouring low density CDM models (Omega(0) = 0.35) with or without a cosmological constant.