Importance of Cluster Structural Evolution in Using X-ray and SZE Galaxy   Cluster Surveys to Study Dark Energy
  We examine the prospects for measuring the dark energy equation of state parameter w within the context of the still uncertain redshift evolution of galaxy cluster structure. We show that for a particular X-ray survey (SZE survey) the constraints on w degrade by roughly a factor of 3 (factor of 2) when one accounts for the possibility of non--standard cluster evolution. With followup measurements of a cosmology independent, mass--like quantity it is possible to measure cluster evolution, improving constraints on cosmological parameters (like w Omega_M). We examine scenarios where 1%, 10% and 100% of detected clusters are followed up, showing that even a modest followup program can enhance the final cosmological constraints. For the case of followup measurements on 1% of the cluster sample with an uncertainty of 30% on individual cluster mass--like quantities, constraints on w are improved by a factor of 2 to 3. For the best case scenario of a zero curvature universe, these particular X-ray and SZE surveys can deliver uncertainties on w of ~4% to 6%. 
Subhabrata Majumdar and Joseph J. Mohr (University of Illinois)