Constraining Dark Energy with DEEP2

Abstract

The DEEP2 survey has now completed half of its planned three-year lifespan, and we have collected approximately 50% of the data, putting us exactly on schedule. The survey plan calls for spectroscopic coverage by July of 2005 of \~60,000 galaxies over 3.5 square degrees to a limiting magnitude of R_{AB}=24.1; the great majority of these objects are at 0.7<z<1.4. We describe here one method by which DEEP2 can set constraints on the equation of state parameter of the Dark Energy, w. By counting the number of virialized groups and clusters we find in redshift space as a function of their redshift and internal velocity dispersion, we probe both the volume element and the growth of structure at z~1, each of which depends on w. Studies of early DEEP2 data indicate that the method is likely to work, and preliminary indications are that a total of ~250 small groups will be counted in the full survey, leading to a constraint δw ~ 0.1 if combined with both the velocity dispersion distribution of z~0 clusters from the Sloan Digital Sky Survey and an independent measurement of σ_8. We also provide a general description of the DEEP2 observations and target selection, including the algorithm by which galaxies are placed on slitmasks, to provide context for discussion of DEEP2 cluster samples.