1. CTIO Camera Mtg - Dec ‘03 Studies of Dark Energy with Galaxy Clusters Joe Mohr Department of Astronomy Department of Physics University of Illinois

2. CTIO Camera Mtg - Dec ‘03 Dark Energy and Its Equation of State Expansion history of the universe depends on the amount and nature of dark energy Density Parameter Equation of State Parameter Expansion History

3. CTIO Camera Mtg - Dec ‘03 How Can One Study the Dark Energy? 1. Measuring (relative) distances or volumes out to z~2 2. Measuring the growth rate of cosmic structures 3. Detecting the very large scale, low contrast feature in the power spectrum of density fluctuations 4. Laboratory experiments? 5. Theoretical progress Surveys of galaxy clusters provide the first three Spergel et al 2003 Current Constraints

4. CTIO Camera Mtg - Dec ‘03 Cluster Survey Studies of the Dark Energy: Complementary and Competitive Figure to right shows self-calibrating constraints for a particular survey. With fiducial model taken from WMAP (  8 =0.84,  m =0.27  k =0) there are 29000 clusters in the 4000 deg 2 SPT survey. We assume 30% accurate masses are available for 100 clusters between z of 0.3 and 1.2 The joint constraints on the equation of state parameter and matter density are shown when letting curvature float (dashed) and fixing it at zero (solid) Marginalized w 68% uncertainty is 0.046 (flat) or 0.071 (curvature varying) Parameter degeneracies are quite complementary to those from SNAP and from WMAP (or Planck) SPT: Majumdar & Mohr SNAP: Perlmutter & Schmidt WMAP: Spergel et al

5. CTIO Camera Mtg - Dec ‘03 Cluster Redshift Distribution is Sensitive to the Dark Energy Equation of State Raising w at fixed  E : decreases volume surveyed Volume effect Growth effect decreases growth rate of density perturbations w constraints:

6. CTIO Camera Mtg - Dec ‘03 Self-calibration in Galaxy Cluster Studies of the Dark Energy High yield cluster surveys can in principle deliver percent level constraints on the equation of state of the dark energy and many other cosmological parameters of interest Haiman, Mohr & Holder 2000 Holder, Haiman & Mohr 2001 Weller et al 2001 Levine et al 2002 Hu & Kravtsov 2003 Majumdar & Mohr 2003 Hu 2003 Majumdar & Mohr 2003b Working Requirements: 1.Hierarchical structure formation theory is correct 2.A mass-observable relation exists that can be used to estimate cluster halo masses from observables like X-ray luminosity, galaxy light, weak lensing shear, SZE luminosity 3.Crude redshift estimates are available for each cluster detected in the survey The last three papers have shown that high yield cluster surveys can constrain cosmology while solving for the nature and evolution of the mass-observable relation.

7. CTIO Camera Mtg - Dec ‘03 Some Cluster Surveys SZE surveys: SPT [4000deg 2, >10 4 clusters, 90% z<1, 2007] APEX [400deg 2, >10 3 clusters, 90% z<1, 2005] X-ray surveys: XMM/Chandra serendipitous [2004+] DUO [5000+deg 2, >10 4 clusters, >95% z<1, 2008?] Large Optical Surveys extending to z~1: RCS2 [1000deg 2,>10 4 clusters, >90% z<1, 2004+] CTIO Camera [2008], LSST [2012], SNAP [2011]

8. CTIO Camera Mtg - Dec ‘03 Cluster Followup Photometric Depth Estimate r=24.5 (Vega) will detect 10 galaxies in z=1 cluster near the detection threshold of the SPT survey (M~2x10 14 M o ). Will detect more than this at lower redshift and higher mass. Adopt limits g=25, i=24.0,z=23.5 (cluster galaxies detected in r are undetected in g at z=1, but they are detected in i and z), corresponding to ~15 minute exposures Reminder: 5000 deg 2 survey with CTIO weather stats will have ~10% contingency with 2 deg 2 camera Strategy for Survey Could carry out half-depth, 4 band survey over ~3000deg 2 in a year Depth would be ~0.5mag shallower. SPT cluster science possible in 2009 Time domain astronomy (AGN/QSOs) possible with additional layer of photometry in the following years