1. Berkeley, 16 th – 18 th May 2004Wide-Field Imaging from Space Weak lensing with GEMS Galaxy Evolution from Morphologies and SEDS Catherine Heymans Max-Planck-Institute for Astronomy, Heidelberg & the GEMS collaboration: Michael Brown, Marco Barden, John Caldwell, Boris Haussler, Knud Jahnke, Hans-Walter Rix (PI), Steve Beckwith, Eric Bell, Andrea Borch, Sharda Jogee, Dan McIntosh, Klaus Meisenheimer, Chien Peng, Sebastian Sanchez, Rachel Somerville, Andy Taylor, Lutz Wisotski, Chris Wolf.

2. Berkeley, 16 th – 18 th May 2004Wide-Field Imaging from Space GEMS: HST’s largest colour mosaic GEMS two-colour imaging. m AB (F606W) = 28.3 m AB (F850LP) = 27.1 (5σ depths for compact sources). (Rix et al. 2004) z = F850LP V = F606W GOODS imaging. Area ~ 28 x 28 arcmins centred on the Chandra Deep Field South ~ 150 HDF HST imaging: resolve morphology, mergers and structural properties. A large sample ~10,000 galaxies (R vega < 24) have redshifts accurate to 2%, and rest frame luminosities from COMBO-17 (Wolf et al. 2004)

3. Berkeley, 16 th – 18 th May 2004Wide-Field Imaging from Space GEMS: www.mpia.de/GEMS/gems.htm SkyWalker: www.aip.de/~ssa/gems/swwww.mpia.de/GEMS/gems.htmwww.aip.de/~ssa/gems/sw

4. Berkeley, 16 th – 18 th May 2004Wide-Field Imaging from Space GEMS science goals : galaxy evolution since z~1 Analyse the frequency of galaxies as a function of multi-parameter space (z,L,r,morphology,M,SED….) Bulges and spheroids Disk galaxies Interactions and mergers Bell et al. 2004, McIntosh et al. 2004, Barden et al. 2004, Wolf et al. 2004, Jogee et al. 2004, Jahnke et al. 2004; Sánchez et al. 2004 GEMS is perfect test data for future space-based weak lensing surveys Weak gravitational lensing studies: –Cosmic shear (Heymans et al. 2004) –Galaxy-galaxy lensing –3D lensing incorporating COMBO-17 redshifts

5. Berkeley, 16 th – 18 th May 2004Wide-Field Imaging from Space The ACS camera imaging properties 1.Geometric distortions Tilted focal surface of ACS wrt optical axis yields strong geometric distortions Additional small corrections required for the effect of differential velocity aberration. During frame combination with multidrizzle, images are reinterpolated onto a regular grid Residual distortions < 0.01% Meurer et al. 2002

6. Berkeley, 16 th – 18 th May 2004Wide-Field Imaging from Space The PSF is strongly non-Gaussian and varies for different filters Kaiser Squires & Broadhurst 1995 (KSB) PSF correction is applied as a function of galaxy size V band z band Jahnke et al. 2004 The ACS point spread function distortion

7. Berkeley, 16 th – 18 th May 2004Wide-Field Imaging from Space PSF anisotropy 95% of GEMS imaging taken within the space of 20 days → stable PSF Wide-field ~1000 stars map anisotropy of PSF consistenty within data set without relying on models (Tiny-Tim) or archived stellar cluster imaging Distortions ~ 5% After correction < 0.1% Before PSF correction After PSF correction PSF for GOODS & GEMS differ in magnitude and direction ~2% due to different dithering patterns and time variation in the PSF. CTE signature not seen.

8. Berkeley, 16 th – 18 th May 2004Wide-Field Imaging from Space E/B mode decomposition E/B correlators Crittenden et al. 2001 Schneider et al. 2002 B-mode = Noise + systematics EB E-mode = Lensing signal + noise + systematics

9. Berkeley, 16 th – 18 th May 2004Wide-Field Imaging from Space Cosmic Shear analysis of GEMS Weak lensing by large scale structure distorts background images, inducing correlations in the observed ellipticities of galaxies.

10. Berkeley, 16 th – 18 th May 2004Wide-Field Imaging from Space Cosmological parameter estimation σ 8 (Ω m /0.27) 0.67 = 0.74 ± 0.17 Note this does not include cosmic variance! CDFS is a factor of 2 underdense in massive galaxies. Marginalised over z m =0.95 ± 0.1. We assume WMAP priors on H 0, Ω m + Ω Λ = 1, and a Smith et al. 03 non-linearity correction

11. Berkeley, 16 th – 18 th May 2004Wide-Field Imaging from Space Space-based imaging vs ground Space-based imaging has a significantly higher surface density of resolved sources, which can probe the matter density power spectrum at higher redshifts than will ever be feasible from the ground. GEMSCOMBO-17 (Brown et al. 2003) ~ 100 galaxies per sq arcmin~ 35 galaxies per sq arcmin

12. Berkeley, 16 th – 18 th May 2004Wide-Field Imaging from Space Galaxy ellipticity measured in COMBO-17 and GEMS e 1, e 2 COMBO-17 & GEMS KSB shape determination from space-based data is less noisy Lower redshift sub-sample of galaxies imaged by GEMS and resolved in COMBO-17

13. Berkeley, 16 th – 18 th May 2004Wide-Field Imaging from Space Conclusions HST ACS is an excellent instrument for weak lensing studies But the ACS PSF varies with time – GOODS and GEMS have different PSF patterns – important for COSMOS to model time variation This anaylsis has used KSB. A wealth of shape information is avaliable with space based data – future analysis will take full advantage of our high resolution imaging using shapelets (Refregier & Bacon 2003) and maximum likelihood model fitting ( Miller, Heymans & Heavens 2004). GEMS combined with COMBO-17 is a great test case to compare ground and space-based imaging for weak lensing studies We find a higher S/N estimates of the shear correlation function from a subsample of COMBO-17 resolved galaxies when the galaxy shapes are determined from space based imaging. Cosmic shear has been detected from ¼ sq degree HST mosaic and used place joint constraints on σ 8 and Ω m.

14. Berkeley, 16 th – 18 th May 2004Wide-Field Imaging from Space

15. Berkeley, 16 th – 18 th May 2004Wide-Field Imaging from Space

16. Berkeley, 16 th – 18 th May 2004Wide-Field Imaging from Space E/B mode decomposition Crittenden et al. 2001 Schneider et al. 2002 E-mode = Lensing signal + noise + systematics B-mode = Noise + systematics EB

17. Berkeley, 16 th – 18 th May 2004Wide-Field Imaging from Space Ω m = 0.3

18. Berkeley, 16 th – 18 th May 2004Wide-Field Imaging from Space Mimicking weak lensing 1.PSF distortions 2.Geometric distortions 3.CTE degradation 4.Object selection bias – tested with simulations 5.Intrinsic galaxy alignments <2% (Heymans et al. 2004) Good agreement between galaxy ellipticity parameters measured in the z and V band images

19. Berkeley, 16 th – 18 th May 2004Wide-Field Imaging from Space Space-based imaging vs ground COMBO-17 GEMS

20. Berkeley, 16 th – 18 th May 2004Wide-Field Imaging from Space Space-based imaging vs ground COMBO-17 GEMS

21. Berkeley, 16 th – 18 th May 2004Wide-Field Imaging from Space E/S0 Sa-Sm Peculiar/ Interacting Weak Interg/ Compact Barden et al. 2004 Surface brightness dimming of disk galaxies with cosmic time Bell et al. 2004 Galaxies have a bi-modal colour distribution to z~1, and are also roughly bi-modal by morphology