Studies of Dark Energy with Galaxy Clusters

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Studies of Dark Energy with Galaxy Clusters
Joe Mohr Department of Astronomy Department of
Physics University of Illinois
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Dark Energy and Its Equation of State
Expansion history of the universe depends on the
amount and nature of dark energy
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How Can One Study the Dark Energy?

1. Measuring (relative) distances or volumes out to
   z2
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

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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 (s80.84, Wm0.27
  Wk0) there are 29000 clusters in the 4000 deg2
  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
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Cluster Redshift Distribution is Sensitive to the
Dark Energy Equation of State
w constraints

• Raising w at fixed WE
• decreases volume surveyed

• decreases growth rate of density perturbations

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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
• Hierarchical structure formation theory is
  correct
• 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
• 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.
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Some Cluster Surveys

• SZE surveys
• SPT 4000deg2, gt104 clusters, 90 zlt1, 2007
• APEX 400deg2, gt103 clusters, 90 zlt1, 2005
• X-ray surveys
• XMM/Chandra serendipitous 2004
• DUO 5000deg2, gt104 clusters, gt95 zlt1, 2008?
• Large Optical Surveys extending to z1
• RCS2 1000deg2,gt104 clusters, gt90 zlt1, 2004
• CTIO Camera 2008, LSST 2012, SNAP 2011

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Cluster Followup

• Photometric Depth
• Estimate r24.5 (Vega) will detect 10 galaxies in
  z1 cluster near the detection threshold of the
  SPT survey (M2x1014Mo). Will detect more than
  this at lower redshift and higher mass.
• Adopt limits g25, i24.0,z23.5 (cluster
  galaxies detected in r are undetected in g at
  z1, but they are detected in i and z),
  corresponding to 15 minute exposures
• Reminder 5000 deg2 survey with CTIO weather
  stats will have 10 contingency with 2 deg2
  camera
• Strategy for Survey
• Could carry out half-depth, 4 band survey over
  3000deg2 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