Constraining Dark Energy with DEEP2

TL;DR

The DEEP2 survey aims to constrain dark energy's equation of state by analyzing galaxy groups and clusters at redshift ~1, using spectroscopic data to measure structure growth and volume changes.

Contribution

This paper introduces a method to constrain dark energy parameters by counting virialized galaxy groups and clusters in redshift space within the DEEP2 survey.

Findings

Preliminary data suggests counting ~250 small groups will constrain w to ~0.1.

The method combines group counts with SDSS data and _8 measurements.

DEEP2's approach effectively probes structure growth and volume at zrom galaxy surveys.

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 \delta w ~ 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 \sigma_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.