Cosmic Shear with HST

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• Cosmic Shear with HST
• Jason Rhodes, JPL
• Galaxies and Structures Through Cosmic Times
• Venice 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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Weak Gravitational Lensing
Weak lensing effect cannot be measured from any
individual galaxy. Must be measured
statistically over many galaxies
zgalaxy1
zobserver0
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.
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How Gravitational Lensing Works

• 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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E and B modes
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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
ACS Parallel Survey
COSMOS
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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
zgt1.5
1.1ltzlt1.5
0.8ltzlt1.1
0.4ltzlt0.8
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Cosmological parameter constraints
?8
-3.0 -2.5 -2.0 -1.5
-1.0 -0.5 0.0
w
w
?m
Courtesy Joel Bergé
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Combined Errors
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Complementary Error bars