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Probing the Dark Universe with Weak Gravitational Lensing

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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Probing the Dark Universe with Weak Gravitational Lensing

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  1. 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 IDM2004, September, Edinburgh

  2. 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) IDM2004, September, Edinburgh

  3. Gravitational Lensing • Hubble Space Telescope deep field of a galaxy cluster – the large gravitational lens, Abell 2218. IDM2004, September, Edinburgh

  4. Gravitational Lensing • A simple scattering experiment: Observer Galaxy cluster/lens Background source IDM2004, September, Edinburgh

  5. Shear matrix Shear matrix Gravitational Lens Distortions • Galaxy ellipticity, e: • Lensing effect: e’ = e + 2 g • On average <e> = 0. • So <e’ >=2g. • Shear matrix: g = g1 + g2 IDM2004, September, Edinburgh

  6. 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.) IDM2004, September, Edinburgh

  7. Mapping the Dark Matter • From shear to projected density (Kaiser & Squires, 1993): Surface potential Surface density = S/Sc (Courtesy A. Refregier) IDM2004, September, Edinburgh

  8. A901a A901b A902 Supercluster Abell 901/2 in COMBO-17 Survey • z=0.16 • R=24.5 1/2 deg 3Mpc/h (Gray & Taylor, et al., 2002, ApJ, 568,141) IDM2004, September, Edinburgh

  9. Mass and light in Supercluster A901/2 Dark Matter contours, k. Elliptical galaxy light shading. Error: Dk=0.02 (1-contour) (Gray & Taylor, et al., 2002, ApJ, 568,141) IDM2004, September, Edinburgh

  10. 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 IDM2004, September, Edinburgh

  11. Observer Galaxy clusters/lenses Background source Mapping the Dark Matter in 3-D • With source distances this can be exactly solved to • recover the 3-D Newtonian potential: (Taylor 2001) IDM2004, September, Edinburgh

  12. 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 Dz=0.01. (Bacon & Taylor MN 2003; Taylor, et al MN 2004) (Bacon & Taylor, 2003; Hu & Keeton, 2002) IDM2004, September, Edinburgh

  13. A901a A901a A901b CB1 A901b A902 A902 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) IDM2004, September, Edinburgh Taylor, et al, 2004 MN, in press

  14. The 3-D dark matter potential and galaxy number density fields • Potential Field: • Galaxy number density: IDM2004, September, Edinburgh Taylor, et al, 2004 MN, in press

  15. A901/2 + CB1 Cluster parameters Cluster Redshift M (<0.5Mpc) L(<0.5Mpc) 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) IDM2004, September, Edinburgh

  16. Cosmic Shear • Lensing by the large-scale dark matter distribution. • First detected by 4 groups in 2000. IDM2004, September, Edinburgh

  17. 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 IDM2004, September, Edinburgh

  18. 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) Shear Amplitude Standard LCDM model Multipoles Brown, Taylor, et al, 2003, MNRAS, 341, 100 IDM2004, September, Edinburgh

  19. CMB 2dF s8 = 0.73+/-0.05 s8 WMAP Wm= 0.27+/-0.02 GL Wm Results from Cosmic Shear • Combine with 2dF Galaxy Redshift Survey & pre-WMAP CMB s8(Wm/0.3)0.49=0.71+/-0.09 Lewis & Bridle (2002) Percival et al (2002) (h=0.72, t=0.1) Brown, Taylor, et al, 2003, MNRAS, 341, 100 IDM2004, September, Edinburgh

  20. Cosmology 3-D Cosmic Shear • Shear probes the density field at different redshifts: Shear-shear cross-power Observer Redshift IDM2004, September, Edinburgh

  21. 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 IDM2004, September, Edinburgh (Bacon & Taylor, et al 2004, MN)

  22. Geometric test of Dark Energy (Bhuvnesh Jain & AT, 2003, Phys Rev Lett, 91,1302) • Depends only on WV, w = p/r (and Wm+WK). Observer Galaxy cluster/lens z1 zL z2 IDM2004, September, Edinburgh

  23. Geometric test of Dark Energy • Estimate parameters by minimising c2 -fit over all source configurations. Observer Galaxy cluster/lens z1 zL z2 IDM2004, September, Edinburgh

  24. w WV Geometric test of Dark Energy (with Tom Kitching and David Bacon) • Geometric test applied to A901/2 clusters. • Dw~0.8 from 3 clusters. • Uncertainty scales as: • ~1% for darkCAM on VISTA. A901/2 WMAP IDM2004, September, Edinburgh

  25. Measuring the evolution of Dark Energy • Measure Wvand w(a)=w0+wa(1-a). • Estimate error for SNAP (zm=1.5). • 10% of sky: Dw=~1%, Dwa=~10% wa=0 w0 wa w0 WV IDM2004, September, Edinburgh Jain & Taylor, PhysRevLett, 2003

  26. 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. IDM2004, September, Edinburgh

  27. 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. IDM2004, September, Edinburgh

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