Galaxy Clusters, Dark Energy and Structure Formation

Galaxy clusters have long been important tools for studying cosmology. Recent measurements of the X-ray and near infrared properties of galaxy clusters provide compelling evidence that we live in a low matter density universe. Surveys for galaxy clusters that use the X-ray emission and the distortion that hot cluster gas introduces into the spectrum of the cosmic microwave background (the Sunyaev-Zeldovich effect) further support a low matter density universe. Taken together with observations of the cosmic microwave background anisotropy, which indicate we live in a geometrically flat universe, cluster constraints on the matter density imply a dominant dark energy component, in agreement with the analyses of supernova Ia distance measurements.

A remaining problem is to determine the nature of this dark energy. Large galaxy cluster surveys provide a means of precisely measuring the equation of state of the dark energy. One such survey will be carried out with an 8m mm-wave telescope located at the South Pole. The design of this survey and the followup to obtain cluster redshifts is critical to minimizing systematic errors in measurements of the amount and nature of the dark energy. Current observations of cluster structural evolution with Chandra provide some insights into the likely success of future cluster surveys.