Berkeley, 16 th – 18 th May 2004 Wide-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.
Transcript
Berkeley, 16th – 18th May 2004 Wide-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.
Wide-Field Imaging from SpaceBerkeley, 16th – 18th May 2004
GEMS: HST’s largest colour mosaic
GEMS two-colour imaging.
mAB(F606W) = 28.3
mAB(F850LP) = 27.1
(5σ depths for compact sources).(Rix et al. 2004)
z = F850LPV = 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 (Rvega< 24) have redshifts accurate to 2%, and rest frame luminosities from COMBO-17 (Wolf et al. 2004)
Wide-Field Imaging from SpaceBerkeley, 16th – 18th May 2004GEMS: www.mpia.de/GEMS/gems.htm SkyWalker: www.aip.de/~ssa/gems/sw
Wide-Field Imaging from SpaceBerkeley, 16th – 18th May 2004
GEMS science goals : galaxy evolution since z~1Analyse 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 SpaceBerkeley, 16th – 18th May 2004
• 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 SpaceBerkeley, 16th – 18th May 2004
• 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
Wide-Field Imaging from SpaceBerkeley, 16th – 18th May 2004
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.
Wide-Field Imaging from SpaceBerkeley, 16th – 18th May 2004
E/B mode decomposition
E/B correlators
Crittenden et al. 2001 Schneider et al. 2002
B-mode = Noise + systematics
E B
E-mode = Lensing signal + noise + systematics
Wide-Field Imaging from SpaceBerkeley, 16th – 18th May 2004
Cosmic Shear analysis of GEMSWeak lensing by large scale structure distorts background images, inducing correlations in the observed ellipticities of galaxies.
Wide-Field Imaging from SpaceBerkeley, 16th – 18th May 2004
Cosmological parameter estimation
σ8(Ωm/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 zm=0.95 ± 0.1. We assume WMAP priors on H0, Ωm + ΩΛ
= 1, and a Smith et al. 03 non-linearity correction
Wide-Field Imaging from SpaceBerkeley, 16th – 18th May 2004
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.
GEMS COMBO-17 (Brown et al. 2003)
~ 100 galaxies per sq arcmin ~ 35 galaxies per sq arcmin
Wide-Field Imaging from SpaceBerkeley, 16th – 18th May 2004
Galaxy ellipticity measured in COMBO-17 and GEMS
e1, e2 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
Wide-Field Imaging from SpaceBerkeley, 16th – 18th May 2004
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 SpaceBerkeley, 16th – 18th May 2004
Wide-Field Imaging from SpaceBerkeley, 16th – 18th May 2004
Wide-Field Imaging from SpaceBerkeley, 16th – 18th May 2004
E/B mode decomposition
Crittenden et al. 2001 Schneider et al. 2002
E-mode = Lensing signal + noise + systematics
B-mode = Noise + systematics
E B
Wide-Field Imaging from SpaceBerkeley, 16th – 18th May 2004
Ωm = 0.3
Wide-Field Imaging from SpaceBerkeley, 16th – 18th May 2004
Mimicking weak lensing1. 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
Wide-Field Imaging from SpaceBerkeley, 16th – 18th May 2004
Space-based imaging vs groundCOMBO-17GEMS
Wide-Field Imaging from SpaceBerkeley, 16th – 18th May 2004
Space-based imaging vs groundCOMBO-17GEMS
Wide-Field Imaging from SpaceBerkeley, 16th – 18th May 2004
E/S0Sa-SmPeculiar/InteractingWeak 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
