A promising way of finding high-redshift clusters is to perform deep, large-scale SZE surveys, taking advantage of the redshift independence of the SZE. Such surveys will provide large catalogs of galaxy clusters, many of which will be at high redshift. The redshift evolution of the number density of galaxy clusters is critically dependent on the underlying cosmology, and in principle can be used to determine the equation of state of the "dark energy" (e.g., Haiman et al., 2001; Holder et al., 2000; Holder et al., 2001). Figure 7 illustrates the dependence of the evolution of cluster number density on cosmology (Holder et al., 2000). All three cosmologies are normalized to the local cluster abundance. Notice that for low-m cosmologies, there are a significant number of galaxy clusters with z > 1.
Figure 7. Expected number counts of galaxy clusters from an upcoming dedicated interferometric SZE survey array. The curves are very different for the three different cosmologies, having been normalized to the local cluster abundance. The two sets of curves are slightly different treatments of the mass limits. Notice that for low-m cosmologies, there are a significant number of galaxy clusters with z > 1. The cosmologies in the figure are (m, , 8): CDM (0.3, 0.7, 1.0); OCDM (0.3, 0.0, 0.6); and CDM (1.0, 0.0, 1.0). See (Holder et al., 2000) for details.
There are a number of dedicated SZE experiments under construction that will perform deep, large-scale SZE surveys. In the next few years, there are a number of interferometric approaches that should find hundreds of galaxy clusters. Bolometer array based SZE experiments should find roughly thousands of clusters just one year after the interferometric experiments. The following generation of bolometer array based SZE experiments should measure tens of thousands of galaxy clusters on a roughly five-year time scale. The possible systematics that could affect the yields of SZE surveys are presently too large to realize the full potential of a deep SZE survey covering thousands of square degrees. These systematics include, for example, the uncertainties on the survey mass detection limit owing to unknown cluster structure and cluster gas evolution. These systematics can begin to be addressed through detailed follow-up observations of a moderate-area SZE survey. High-resolution SZE, X-ray, and weak lensing observations will provide insights into the evolution and structure of the cluster gas. Numerical simulations directly compared and normalized to the SZE yields should provide the necessary improvement in our understanding of the mass function.