Harvard-Smithsonian Center for Astrophysics Colloquium Galaxy Clusters and the Dark Universe Steve Allen November 14, 2013 Cosmological constraints from observations of galaxy clusters are obtained via two main methods. The first uses measurements of the baryonic mass fraction in the largest, dynamically relaxed clusters. This method provides tight constraints on the mean matter density and, like type Ia supernovae studies, traces the effects of dark energy on the expansion of the Universe directly. The second, independent method uses measurements of the number counts of clusters as a function of mass and redshift. It leads to tight constraints on the amplitude of matter fluctuations and powerful, complementary constraints on dark energy from its impact on the growth of cosmic structure. I will discuss new results from both methods, and outline the prospects for improvement in the near-to-mid term.

• published: 19 Nov 2013
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