Probing Dark Energy with Cosmological Observations

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Probing Dark Energy with
Cosmological Observations

• Fan, Zuhui (Dept. of Astronomy, Peking
  University)
• Representing many colleagues in the team
• Xinmin Zhang (IHEP), Xuelei Chen(NAOC)
  ,Zonghong Zhu (BNU)
• and their fellow posdocs, and students

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• Outline
• Introduction
• Current Status
• Discussion
• Future

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• Introduction
• The development of cosmology is largely
• driven by observations

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• The accelerating expansion of the universe
• ? asks for something new
• Change the Matter content Dark Energy
• Change the theory

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• Cosmological studies on dark energy
• Global expansion of the Universe
• cosmological distances, age,
• The formation and evolution of the
• large-scale structures in the Universe

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• Cosmological observables
• SNeIa luminosity distances
  (Global)
• LSS structure formation
• BAO (angular
  diameter distances)
• CL structure formation
• volume element
  (global)

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• Weak Lensing
  structure formation
• relative
  angular diameter distances
• 
  (global)
• CMB angular
  diameter distance
• 
  (global)
• ISW
  (structure evolution)
• GRB, redshft distortion (growth
  factor)

Most of the observables contain both sides of
information
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• Current observations
• SNeIa Union 307
• (SNLSESSENCEolder ones)
• CMB WMAP5, BOOMERanG,
• CBI, VSA,ACBAR

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• LSS SDSS, 2dFGRS
• Weak Lensing CITO, CFHTLS,

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• Current constraints on EoS of dark energy
• Komatsu et al. (2008) (WMAP distance priors )

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• Xia et al. (2008) MCMC
• dark energy perturbations included (w cross
  -1)

Cosmological constant remains to be an excellent
fit Quintom models with w crossing -1
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• Discussions
• Dark energy perturbations
• The existence of DE perturbations is
  inevitable
• for dynamical dark energy models
• By allowing w to cross -1, DE perturbations
  have
• to be analyzed properly divergent terms if
  at w-1

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• Zhao et al. (2006), Xia et al. (2006)
• Dark energy perturbations are analyzed for
  two-fields
• Quintom models, and it is found that they are
  well
• behaved at the crossing point w-1
• ? develop a method and implement it into MCMC
• For (2) match (1) and (3) and the boundary and

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• Effects of DE perturbations

Notable influence on the ISW effect at small
l Zhao et al. (2006)
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• EoS of dark energy Xia et al. (2006)

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• Distance priors from CMB

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• easy to use avoid the effect of DE
  perturbations
• Caveats model dependent
• information loss (ISW)
• Li et al. (2008)

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• Li et al. (2008)
• 
  
• 
  somewhat
• 
  model
• 
  dependent
• 
  not sensitive
• 
  to DE models

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• information loss
• 
  without including
• 
  DE perturbations
• 
  ISW plays significant
• 
  roles
• 
  with DE perturbations
• 
  the DE information
• 
  is almost fully
• 
  contained in the
• 
  distance priors

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• Systematic effects
• For future high precision observations,
  systematic
• effects will become dominant source of errors.
• Thus detailed understanding are necessary.
• For example
• Weak lensing

redshift distribution of source galaxies
photo-z measurement intrinsic alignments of
source galaxies shear-ellipticity
correlation Nonlinear power spectrum
observational systematics
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• Sun et al. (2008)
• photo-z
• catastrophic errors

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• adding u-band observations
• spectroscopic calibrations
• finer bins in tomographic lensing analyses

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DETF

• Future
• The future of
• Dark is bright

Through investigations are needed