Weak lensing with GEMS G alaxy E volution from M orphologies and S EDS

1. Weak lensing with GEMSGalaxy 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. Wide-Field Imaging from Space

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

3. GEMS: www.mpia.de/GEMS/gems.htm SkyWalker: www.aip.de/~ssa/gems/sw Wide-Field Imaging from Space

4. 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 Wide-Field Imaging from Space

5. The ACS camera imaging properties • 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 Wide-Field Imaging from Space

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

7. PSF anisotropy Before PSF correction • 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% 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. Wide-Field Imaging from Space

8. E/B mode decomposition E B E-mode = Lensing signal + noise + systematics B-mode = Noise + systematics E/B correlators Crittenden et al. 2001 Schneider et al. 2002 Wide-Field Imaging from Space

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

10. Cosmological parameter estimation Marginalised over zm=0.95 ± 0.1. We assume WMAP priors on H0, Ωm + ΩΛ= 1, and a Smith et al. 03 non-linearity correction σ8(Ωm/0.27)0.67 = 0.74 ± 0.17 Note thisdoes not include cosmic variance! CDFS is a factor of 2 underdense in massive galaxies. Wide-Field Imaging from Space

11. Space-based imaging vs ground GEMS COMBO-17 (Brown et al. 2003) • 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. ~ 100 galaxies per sq arcmin ~ 35 galaxies per sq arcmin Wide-Field Imaging from Space

12. e1, e2 COMBO-17 & GEMS Galaxy ellipticity measured in COMBO-17 and GEMS Lower redshift sub-sample of galaxies imaged by GEMS and resolved in COMBO-17 KSB shape determination from space-based data is less noisy Wide-Field Imaging from Space

13. 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 σ8 and Ωm. Wide-Field Imaging from Space

14. Wide-Field Imaging from Space

15. Wide-Field Imaging from Space

16. E/B mode decomposition E-mode = Lensing signal + noise + systematics B-mode = Noise + systematics Crittenden et al. 2001 Schneider et al. 2002 E B Wide-Field Imaging from Space

17. Ωm = 0.3 Wide-Field Imaging from Space

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

19. Space-based imaging vs ground COMBO-17 GEMS Wide-Field Imaging from Space

20. Space-based imaging vs ground GEMS COMBO-17 Wide-Field Imaging from Space

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