Measuring Omega0 using cluster evolution

Abstract

The evolution of the abundance of galaxy clusters depends sensitively on the value of the cosmological density parameter, Ω 0 . Recent ASCA data are used to quantify this evolution as measured by the cluster X-ray temperature function. A χ 2 minimisation fit to the cumulative temperature function, as well as a maximum likelihood estimate (which requires additional assumptions about cluster luminosities), lead to the estimate Ω 0 ≈ 0.45 ± 0.2 (1-σ statistical error). Various systematic uncertainties are considered, none of which enhance significantly the probability that Ω 0 = 1. These conclusions hold for models with or without a cosmological constant, i.e. with Λ 0 = 0 or 1 − Ω 0 . The statistical uncertainties are at least as large as any of the individual systematic errors that have been considered here, suggesting that additional temperature measurements of distant clusters will allow an improvement in this estimate. An alternative method that uses the highest redshift clusters to place an upper limit on Ω 0 is also presented and tentatively applied, with the result that Ω 0 = 1 can be ruled out at the 98 per cent confidence level. Whilst this method does not require a well-defined statistical sample of distant clusters, there are still modelling uncertainties that preclude a firmer conclusion at this time.

Terapixel Surveys for Cosmic Shear

“…Hence, these cosmic shear surveys mainly probe weak cosmological lensing produced by clusters of galaxies and compact groups. The constraints provided by cosmic shear are formally similar to those from cluster abundances obtained from counts of clusters in optical or X-ray surveys (Eke et al [11], Eke et al [12], Bridle et al [13]). Depending on the angular scales, the variance of the cosmological convergence writes:…”

Dark Matter in Groups and Clusters of Galaxies

“…Similarly, the comoving maximum of the galaxy power spectrum allows to measure the cosmological curvature (Broadhurst & Jaffe 1999), and prefers a Universe with Ω M = 0.4 ± 0.1. As demonstrated by Bahcall & Fan (1998) and Eke et al (1998), the rate of the evolution of cluster abundance depends strongly on the mean density of the Universe. The cluster abundance method yields for the density a value Ω M = 0.3 ± 0.1.…”

Cosmological parameters

“…But the cluster data at various redshifts are difficult to compare properly since they are rather inhomogeneous. Using just X-ray temperature data, [37] concludes that Ω m ≈ 0.45 ± 0.2, with Ω m = 1 strongly disfavored.…”