Colloquium Bonn June 2 2006

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Cosmological Weak Lensing With SKA in the Planck
era
Y. Mellier
SKA, IAP, October 27 , 2006
2
Cosmic shear propagation of light through the
cosmic web
Gpc
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Cosmological distortion field projected on the sky
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Weak gravitational lensing and cosmologyLight
propagation in inhomogeneous universes
ds2c2dt2 - a2(t) dw2 fK2(w) d?2
Deflection angle
Bartelmann Schneider 2001 Erben 2002
Power spectrum, growth rate of structure
Distances
Both depend on the dark matter and dark energy
content in the Universe
5
Properties of Dark energy in the Planck era
measuring very small effects, DE dominated era at
small z (good for WL)
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Cosmic shear surveys and dark cosmological models
exploring the power spectrum
z2
z1
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Shapes and Shear practicing WL
Mellier 1999
?
PSF anisotropy correction Derived from star
shape analysis. Image quality of primary
importance for weak lensing
?s ?i noise systematics.
d 2? (weak lensing regime)
Reliability of results depends on PSF analysis
Assume sources orientation is isotropic
Weak lensing regime ? 2? ?Shear? noise
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I. The shape and amplitude of the signal is in
very good agreement with gravitational
instability paradigm in a CDM-dominated
universe. (Blandford el al 1991, Miralda-Escudé
1991, Kaiser 1992, 1998, Bernardeau et al 1997,
Jain Seljak 1997, Schneider et al 1998)
Top-Hat Shear variance (observed)
Top-Hat Shear variance (predicted)
Map variance
Non-Linear
Non_linear
Linear
Linear
Refregier et al 2002
Bartelmann Schneider 2001 theoretical
predictions from the gravitational instability
scenario

See Bacon et al 2000 , 2001 Kaiser et al.
2000 Maoli et al. 2000 Rhodes et al
2001 Refregier et al 2002 van Waerbeke et
al. 2000 van Waerbeke et al. 2001, 2005
Wittman et al. 2000 Hammerle et al. 2001
Hoekstra et al. 2002 Brown et al. 2003
Hamana et al. 2003 Jarvis et al. 2003
Casertano et al 2003 Rhodes et al 2004
Massey et al. 2004 Heymans et al 2004
Semboloni et al 2006 Hoekstra et al 2005,
Hetterscheidt et al 2006, Schrabback et al 2006,
Fu et al 2006
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Cosmic shear and dark energy
Cosmic shear is a unique way to explore the dark
matter power spectrum P(k,z) directly

• Galaxy ellipticity
• Galaxy redshift

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Cosmic shear and dark energy
Cosmic shear is a unique way to explore the dark
matter power spectrum P(k,z) directly

• Galaxy ellipticity
• Galaxy redshift

• Power spectrum
• Bispectrum
• Decoupling geometry/P(k)
• Tomography
• Control systematics

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Cosmic shear and dark energy
Cosmic shear is a unique way to explore the dark
matter power spectrum P(k,z) directly

• Galaxy ellipticity
• Galaxy redshift

• Power spectrum
• Bispectrum
• Decoupling geometry/P(k)
• Tomography
• Control systematics

Dark energy properties
12
Cosmic shear and dark energy
Cosmic shear is a unique way to explore the dark
matter power spectrum P(k,z) directly

• Need high image quality
• Accurate PSF correction
• Accurate galaxy redshift
• Large FOV for linear power spectrum
• Large FOV for cosmic variance

• Galaxy ellipticity
• Galaxy redshift

• Power spectrum
• Bispectrum
• Decoupling geometry/P(k)
• Tomography
• Control systematics

Dark energy properties
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Errors and systematics uncertainties

• PSF corrections
• Redshift distribution
• Clustering
• Contamination by overlapping galaxies
• Intrinsic alignement
• Intrinsic foreground/backgound correlations
• Sampling variance
• Non-linear variance
• Non-linear dark matter power spectrum
• cosmic variance (survey size, survey topology,
  depth)

14
Exploring DE as function of redshift still far
from getting wa
CSLSSNLS
SNSL 5yr
CSLS 5yr DeepWide 170/170 deg2
SNLS 5yrs
Jarvis, Jain, Bernstein, Dolney 2005
15
Breaking degeneracies with tomography
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Cosmic shear non-SKA projects
KIDS CFHTLS Wide CFHTLS Deep 3 lens planes
proposed
moderate
5000?
45
VST/VISTA
2010-2015?
proposed
moderate
DUNE
21?
20000? (space)
2012-2018?
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SKA vs. others
DUNE Very Large FOV 10000 deg2 Space excellent
PSF correction No spectro-z Reasonnably good
photo-z? 109 galaxies 2017? SNAP Reasonnable
FOV 1000 deg2 Space excellent PSF correction No
spectro-z Good photo-z 5x108 galaxies gt2015? LSST
Very Large FOV 15000 deg2 Ground reassonably
good PSF correction No-spectro-z Reasonnably good
photo-z 5x109 galaxies 2014?
SKA Very Large FOV 20000 deg2 Radio Excellent
PSF correction Spectro-z 5x109 galaxies gt2020?
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SNAP cosmic shaer 300deg2
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(No Transcript)
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Merit factors
BUT this assumes systematics are controled
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Intrinsic projected ellipticity distribution of
galaxies in the optical/NIR bands
se 0.35
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Intrinsic projected ellipticity of SKA galaxies

• What is se for the SKA sample?
• How does it vary with galaxy type?
• How does it vary with environment?
• How does it vary with redshift?

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Cosmic shear with SKA

• Strong points
• Very large FOV (linear spectrum, cosmic
  variance)
• Excellent sampling of the PSF
• Excellent sampling of galaxies
• Very precise N(z) best for control of
  systematics (e.g. effects of clustering)
• Unknown
• Intrinsic ellipticity dispersion and its
  evolution with redshift
• PSF stability ?
• Weak point
• A bit far as compared to other projects (could
  be an advantage it depends on what other
  projects will find)