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

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

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

Patterns in a shear field

Clusters are patterns in a shear field:

HST Surveys With ACS

GEMS UDF

GOODS

COSMOS

ACS Parallel Survey

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

The PSF Problems

•PSF time variability•CTE degradation

See Rhodes et al 2006, astro-ph/0512170

TinyTim- The PSF Solution

Parametric CTE Correction

Shear-shear correlation functions

E-B mode split

Redshift tomography

Redshift tomography

0.4<z<0.8

0.8<z<1.1

1.1<z<1.5

z>1.5

Cosmological parameter constraints

Courtesy Joel Bergé

8

Ωm

ww

-3.0 -2.5 -2.0 -1.5 -1.0 -0.5 0.0

Combined Errors

Complementary Error bars