1. Cosmological Weak Lensing With SKA in the Planck era Y. Mellier SKA, IAP, October 27, 2006

2. ~ Gpc Cosmic shear : propagation of light through the cosmic web

3. Cosmological distortion field projected on the sky

4. Weak gravitational lensing and cosmology: Light propagation in inhomogeneous universes Bartelmann & Schneider 2001; Erben 2002 ds 2 =c 2 dt 2 - a 2 (t) [dw 2 + f K 2 (w) d  2 ] Distances Power spectrum, growth rate of structure Both depend on the dark matter and dark energy content in the Universe Deflection angle:

5. Properties of Dark energy in the Planck era: measuring very small effects, DE dominated era at small z (good for WL)

6. Cosmic shear surveys and dark cosmological models : exploring the power spectrum z=1 z=2

7. Shapes and Shear: practicing WL PSF anisotropy correction Derived from star shape analysis. Image quality of primary importance for weak lensing =  s +  i + noise + systematics …. Weak lensing regime :  ~ 2  = ‹  S hear ›  + noise Assume sources orientation is isotropic : Mellier 1999 δ ~ 2γ (weak lensing regime) Reliability of results: depends on PSF analysis κ

8. Bartelmann & Schneider 2001 : theoretical predictions from the gravitational instability scenario 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) M ap variance Top-Hat Shear variance (predicted) 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 Refregier et al 2002 Linear Non-Linear Non_linear Linear Top-Hat Shear variance (observed)

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

10. Galaxy ellipticity Galaxy redshift Power spectrum Bispectrum Decoupling geometry/P(k) Tomography Control systematics Cosmic shear and dark energy Cosmic shear is a unique way to explore the dark matter power spectrum P(k,z) directly

11. Galaxy ellipticity Galaxy redshift Power spectrum Bispectrum Decoupling geometry/P(k) Tomography Control systematics Dark energy properties Cosmic shear and dark energy Cosmic shear is a unique way to explore the dark matter power spectrum P(k,z) directly

12. Galaxy ellipticity Galaxy redshift Power spectrum Bispectrum Decoupling geometry/P(k) Tomography Control systematics Dark energy properties Need high image quality Accurate PSF correction Accurate galaxy redshift Large FOV for linear power spectrum Large FOV for cosmic variance Cosmic shear and dark energy Cosmic shear is a unique way to explore the dark matter power spectrum P(k,z) directly

13. 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 w a CSLS 5yr Deep+Wide 170/170 deg 2 SNSL 5yr SNLS 5yrs CSLS+SNLS Jarvis, Jain, Bernstein, Dolney 2005

15. Breaking degeneracies with tomography

16. Cosmic shear: non-SKA projects Survey Sq. Degrees FiltersDepthDatesStatus CTIO751shallowpublished VIRMOS91moderatepublished COSMOS2 (space)1moderatecomplete DLS (NOAO) 364deepcomplete Subaru30?1?deep 2005? observing CFH Legacy 1705moderate 2004-2008 observing RCS2 (CFH) 8303shallow 2005-2007 approved VST/KIDS/ VISTA/VIKING 17004+5moderate 2007-2010? 50%approved DES (NOAO) 50004moderate 2008-2012? proposed Pan-STARRS ~10,000?5?moderate 2006-2012? ~funded LSST15,000?5?deep 2014-2024? proposed JDEM/SNAP 1000+ (space) 9deep 2013-2018? proposed VST/VISTA DUNE 5000? 2010-2015? moderate 4+5 proposed 20000? (space) 2+1? moderate 2012-2018? proposed KIDS + CFHTLS Wide + CFHTLS Deep: 3 lens planes

17. SKA vs. others DUNE: Very Large FOV: 10000 deg2 Space: excellent PSF correction No spectro-z Reasonnably good photo-z? 10 9 galaxies 2017? SNAP: Reasonnable FOV: 1000 deg2 Space: excellent PSF correction No spectro-z Good photo-z 5x10 8 galaxies >2015? LSST: Very Large FOV: 15000 deg2 Ground: reassonably good PSF correction No-spectro-z Reasonnably good photo-z 5x10 9 galaxies 2014? SKA: Very Large FOV: 20000 deg2 Radio: Excellent PSF correction Spectro-z 5x10 9 galaxies >2020?

18. SNAP cosmic shaer: 300deg 2

20. Merit factors BUT: this assumes systematics are controled

21. Intrinsic projected ellipticity distribution of galaxies in the optical/NIR bands σ ε =0.35

22. Intrinsic projected ellipticity of SKA galaxies What is σ ε for the SKA sample? How does it vary with galaxy type? How does it vary with environment? How does it vary with redshift?

23. 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…)