Probing%20the%20Dark%20Universe%20with%20Weak%20Gravitational%20Lensing

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Probing the Dark Universe with Weak Gravitational
Lensing

• Andy Taylor
• Institute for Astronomy, School of Physics,
• University of Edinburgh, Royal Observatory,
• Edinburgh, U.K.

With David Bacon, Meghan Grey, Michael Brown,
Tom Kitching, Chris Wolf, Klaus Meisenheimer,
Bhuvnesh Jain
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The Standard Model of Cosmology

• WMAP, SNIa, 2dFGRS, Sloan Digital Sky Survey
• 70 Dark Energy
• 25 Dark Matter
• 5 Baryonic Matter
• Spatially flat
• Four outstanding problems
• Dark Matter
• Dark Energy
• Inflation
• Galaxy formation

(VIRGO Consortium)
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Gravitational Lensing

• Hubble Space Telescope deep field of a galaxy
  cluster the large gravitational lens, Abell
  2218.

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Gravitational Lensing

• A simple scattering experiment

Observer
Galaxy cluster/lens
Background source
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Gravitational Lens Distortions

• Galaxy ellipticity, e
• Lensing effect
• e e 2 g
• On average ltegt 0.
• So lte gt2g.
• Shear matrix

g g1 g2

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Weak Lensing

• An observable is the shear (2-d tidal) matrix
• The 2-d lensing scalar potential, f, is
  a projected Newtonian potential, F

(Take derivatives on sky.)
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Mapping the Dark Matter

• From shear to projected density (Kaiser
  Squires, 1993)

Surface potential
Surface density
S/Sc
(Courtesy A. Refregier)
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Supercluster Abell 901/2 in COMBO-17 Survey

• z0.16
• R24.5

1/2 deg 3Mpc/h
(Gray Taylor, et al., 2002, ApJ, 568,141)
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Mass and light in Supercluster A901/2
Dark Matter contours, k. Elliptical galaxy light
shading.
Error Dk0.02 (1-contour)
(Gray Taylor, et al., 2002, ApJ, 568,141)
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Mapping the Dark Matter in 3-D

• The lens potential, f, is a radial integral over
  the 3-D
• Newtonian potential, F

Observer
Galaxy clusters/lenses
Background source
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Mapping the Dark Matter in 3-D

• With source distances this can be exactly solved
  to
• recover the 3-D Newtonian potential (Taylor
  2001)

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Is 3-D dark matter mapping practical?

• Shot-noise for 3-D dark matter potential map
• So Wiener filter in redshift
• Can now resolve clusters.
• 3-D lensing quality data already
  exists...COMB0-17 has 17 band photometric
  redshifts with Dz0.01.

(Bacon Taylor MN 2003 Taylor, et al MN 2004)
(Bacon Taylor, 2003 Hu Keeton, 2002)
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The 3-D dark matter potential field

• Potential Field
• Galaxy density

z
1.0
0.8
0.6
0.4
Y
X
(2-s threshold)
Taylor, et al, 2004 MN, in press
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The 3-D dark matter potential and galaxy number
density fields

• Potential Field
• Galaxy number density

Taylor, et al, 2004 MN, in press
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A901/2 CB1 Cluster parameters

• Cluster Redshift M (lt0.5Mpc) L(lt0.5Mpc)
  M/L
• (1013Msun) (1011Lsun)
  (Msun/Lsun)
• A901a 0.16 10.8-2
  24.7 43.7
• A901b 0.16 8.4-2
  13.6 62.2
• A902 0.16 5.1-3
  19.5 26.2
• CB1 0.48 12.0-6
  13.0 92.3

• Estimate projection-free masses of all objects.
• Erratic mass-to-light ratio non-equilibrium
  system.
• Modelling with analytic and numerical methods.

(Taylor, et al, 2004 MN, in press)
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Cosmic Shear

• Lensing by the large-scale dark matter
  distribution.
• First detected by 4 groups in 2000.

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Four random fields in COMBO-17 survey
2-D Dark Matter Maps

• Area 1 sq deg.
• Depth z 0.8.
• Scale 10 Mpc/h.

Chandra Deep Field
South Galactic Pole
S11
FDF
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Cosmic Shear Power Spectrum

• Maximum Likelihood Analysis of Cosmic Shear.
• Measured over 4 random COMBO-17 fields.

R(Mpc/h)
50 5
0.5
zm 0.85/-0.05 from photometric redshifts
(signal) (noise) (noise)
Standard LCDM model
Shear Amplitude
Multipoles
Brown, Taylor, et al, 2003, MNRAS, 341, 100
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Results from Cosmic Shear

• Combine with 2dF Galaxy Redshift Survey
  pre-WMAP CMB

s8(Wm/0.3)0.490.71/-0.09
Lewis Bridle (2002)
Percival et al (2002)
(h0.72, t0.1)
Brown, Taylor, et al, 2003, MNRAS, 341, 100
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3-D Cosmic Shear

• Shear probes the density field at different
  redshifts

Shear-shear cross-power
Observer
Redshift
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The Growth of Dark Matter Clustering

• Evolution of the matter power spectrum

1-sigma
Pm(k,z)
c2-fit to data. First detection of evolution
of Dark matter clustering. A fundamental
prediction of Cosmology.
2-sigma
LCDM
Redshift
(Bacon Taylor, et al 2004, MN)
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Geometric test of Dark Energy

• (Bhuvnesh Jain AT, 2003, Phys
  Rev Lett, 91,1302)
• Depends only on WV, w p/r (and WmWK).

Observer
Galaxy cluster/lens
z1
z2
zL
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Geometric test of Dark Energy

• Estimate parameters by minimising c2 -fit over
  all source configurations.

Observer
Galaxy cluster/lens
z1
z2
zL
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Geometric test of Dark Energy
(with Tom Kitching and David Bacon)

• Geometric test applied to A901/2 clusters.
• Dw0.8 from 3 clusters.
• Uncertainty scales as
• 1 for darkCAM on VISTA.

A901/2
WMAP
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Measuring the evolution of Dark Energy

• Measure Wv and w(a)w0wa(1-a).
• Estimate error for SNAP (zm1.5).
• 10 of sky Dw1, Dwa10

wa0
w0
wa
w0
WV
Jain Taylor, PhysRevLett, 2003
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darkCAM on VISTA

• Comparison of lensing telescopes grasp
• (area x fov) and timescales

VISTA (Visible Infrared Survey Telescope for
Astronomy)
darkCAM

• Proposal to PPARC to start in 2009.
• (PI Taylor)
• w to 1 accuracy.
• 3-D dark matter map of sky.

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Summary

• With 3-D lensing (shear redshifts) we can now
  measure the 3-D Dark Matter distribution.
• Detect the growth of Dark Matter clustering.
• And measure the equation of state of dark energy.
• Can measure dark energy properties in
• near future with darkCAM on VISTA.