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Session 95 - Cosmological Parameters and Large Scale Structure Formation.
Oral session, Friday, January 09
International Ballroom Center,
We use the evolution of the abundance of massive clusters of galaxies to constrain the mass density parameter of the universe, omega, and the amplitude of mass fluctuations, sigma8. By comparing the observed abundance of high-mass clusters at z \sim 0.5 - 1 with the expected abundance in different cosmologies we break the classical degeneracy between omega and sigma8 and determine each of the parameters independently. The relatively weak observed evolution of the cluster abundance with redshift suggests a universe with low-density, omega \sim 0.3 +- 0.1, and high sigma8. Models with Omega = 1 (low sigma8) are excluded by the observed high density of massive distant clusters; such models predict a very low abundance of massive clusters at z>0.5. This method places one of the strongest constraints on cosmology and suggests a low-density, nearly unbiased universe.
