cosmic shear with hst jason rhodes, jpl galaxies and structures through cosmic times venice italy...
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Cosmic Shear with HSTJason Rhodes, JPL
Galaxies and Structures Through Cosmic TimesVenice Italy
March 27, 2006
with Richard Massey, Catherine Heymans & Alexie Leauthaud
The COSMOS Lensing Team: Jean-Paul Kneib, Justin Albert, David Bacon, Joel Berge, Richard Ellis, Cécile Faure, Anton Koekemoer, Yannick Mellier,
Satoshi Miyazaki, John Peacock, Alexandre Refregier, Nick Scoville, Elisabetta Semboloni, Lidia Tasca, James Taylor, Ludovic Van Waerbeke
The ACS Parallel team: Jon Gardner & Nicholas Collins
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If there is any intervening large-scale structure, light follows the distorted path (exaggerated). Background images are magnified and sheared by ~2%, mapping a circle into an ellipse. Lensing is most effective for mass structures half way between the source and the observer.
zobserver=0
zgalaxy≈1
zlens≈0.3–0.5
Weak lensing effect cannot be measured from any individual galaxy.
Must be measured statistically over many galaxies
Weak Gravitational Lensing
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How Gravitational Lensing WorksHow Gravitational Lensing Works
Two component ellipticity
Positive Negative
e1
e2
•Statistical measurement on many galaxies•Lensing induced ellipticities 1-2%•Telescope Point Spread Function (PSF) is the primary systematic concern –it changes e!
•Assume galaxy shears are intrinsically uncorrelated•Need to measure shear quite accurately
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Patterns in a shear field
Clusters are patterns in a shear field:
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HST Surveys With ACS
GEMS UDF
GOODS
COSMOS
ACS Parallel Survey
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COSMOS For WL•2 square degrees•Single orbit F814(I) ACS images•~80 resolved galaxies per square arcmin•versus ~30 from the ground•Redshifts for lenses galaxies•Unique combination of area, depth and resolution•Opens door for unprecedented dark matter maps and statistics at small angular scales
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The PSF Problems
•PSF time variability•CTE degradation
See Rhodes et al 2006, astro-ph/0512170
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TinyTim- The PSF Solution
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Parametric CTE Correction
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Shear-shear correlation functions
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E-B mode split
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Redshift tomography
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Redshift tomography
0.4<z<0.8
0.8<z<1.1
1.1<z<1.5
z>1.5
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Cosmological parameter constraints
Courtesy Joel Bergé
8
Ωm
ww
-3.0 -2.5 -2.0 -1.5 -1.0 -0.5 0.0
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Combined Errors
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Complementary Error bars