Shapelets analysis of weak lensing surveys

Shapelets analysis of weak lensing surveys

Joel Bergé (CEA Saclay)with

Richard Massey (Caltech)

Alexandre Refregier (CEA Saclay)

Joel Bergé (CEA Saclay)with

Richard Massey (Caltech)

Alexandre Refregier (CEA Saclay)

Joel Bergé - 03-22-2006 - Rencontres de Moriond

Observation of cosmic shearObservation of cosmic shear

Distant galaxiesLensed galaxies Dark matter distributionand map of shear

The shear measurement challenge

Shear measurement error is one predominant systematic

Intrinsic ellipticities

PSF (response of the telescope)

Pixelization

Noise

8

-8

-6

-4

-2

6

4

2

0

ShapeletsShapelets

n

m

0 1 2 3 4 5 6 7 8

Complete orthogonal basis functions

Capture all shape information of an object

Simple and analytic form for convolution and shear

Adapted to cosmic shear

n,m

Refregier 2003, Refregier & Bacon 2003, Massey & Refregier 2005

nmax

Shapelets pipelineShapelets pipelineLeast-square fitting of an analytical model (pixelized and convolved with the PSF) to observed data.

Galaxy to be fitted

Shapelet model of the PSF

Shapelet model of the observed galaxy

Residuals

Shapelet model of the galaxy, deconvolved from the PSF

Convolution in shapelets space

Shear estimator

PSF modelPSF modelStars selected then decomposed into shapelets, the order of decomposition depending on data

nmax=28

nmax=10Subaru

CFHT

FWHM ~0.5 arcsec

FWHM ~0.7 arcsec

Wing

PSF interpolationPSF interpolation

Measured PSF

Residuals

Model

CFHT/Megacam D1 field

CFHT/Megacam D1 field

Scale : 8%

Model created by interpolating shapelet

coefficients of stars with a polynomial

Blind test with simulations : STEP (Shear TEsting Programme)

Blind test with simulations : STEP (Shear TEsting Programme)

Heymans et al, 2006Massey et al, 2006, in preparation

Simulation Real image

Aims at comparing and improving existing cosmic shear measurement techniques.Realistic cosmic shear simulations, of ground based weak lensing surveys.

Shapelets STEP resultsShapelets STEP results

1 PSF, 64 input shears

Input shear

Mea

sure

d sh

ear

CFHT/MegacamCFHT/MegacamJ. Bergé, A. Refregier et al

E mode B mode

Mass inversion using wavelets (Starck, Pires & Refregier 2005), cf S. Pires’ poster

SubaruSubaru

QuickTime™ et undécompresseur TIFF (LZW)

sont requis pour visionner cette image.

-3.0

-3.5

-4.0

-4.5

-5.0 37 35.536.036.5

KSB (S. Miyazaki)

S. Miyazaki, R. Massey, J. Bergé, A. Refregier, T. Hamana, R. Ellis

Shapelets (Megacam)

C2

C3

ConclusionsConclusionsShapelets are now reliable for weak lensing high precision measurement

Already used (preliminary results) on Subaru and CFHTLS Deep data

Will be used to analyse current Subaru survey and CFHTLS Wide data

Potential comparison Subaru-CFHT-COSMOS

http://www.astro.caltech.edu/~rjm/shapelets/

http://www.astro.caltech.edu/~jberge/shapelets/

Software package and documentation