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Session 52 - Clusters & Cosmology.
Oral session, Thursday, June 12
North Main Hall C/D,
The evolution of the number density of rich clusters of galaxies provides a powerful constraint on the cosmological density parameter, omega. The evolution of high-mass (Coma-like) clusters is strong in omega=1 models (such as the standard biased CDM model with sigma 0.5, where sigma(8) is the normalization of the power-spectrum required to match the present-day cluster abundance), where the cluster number-density decreases by a factor of 10^3 from z=0 to z=0.5; the same clusters show only mild evolution in low-omega, high-sigma(8) models, where the decrease is a factor of 10. This diagnostic provides a most powerful constraint on omega. Using observations of clusters to z=0.5-1, we find only mild evolution in the observed cluster abundance. We find omega=0.3+-0.1 and sigma(8)=0.85+-0.15. The results imply, if confirmed by future surveys, that we live in a low-density, low-bias universe.
