|Impact of Gravitational Lensing on Cosmology|
Shapelets “Multiple Multipole” Shear Measurement
|Richard Massey a1, Alexandre Refregier a2 and David Bacon a3|
a1 California Institute of Technology, 1200 E. California Blvd., Pasadena, CA 91125, U.S.A. email: [email protected]
a2 Service d'Astrophysique, Bât. 709, CEA Saclay, F-9119 Gif sur Yvette,France
a3 Institute for Astronomy, Blackford Hill, Edinburgh EH9 3HJ, U.K.
The measurement of weak gravitational lensing is currently limited to a precision of $\sim$10% by instabilities in galaxy shape measurement techniques and uncertainties in their calibration. The potential of large, on-going and future cosmic shear surveys will only be realised with the development of more accurate image analysis methods. We present a description of several possible shear measurement methods using the linear “shapelets” decomposition. Shapelets provides a complete reconstruction of any galaxy image, including higher-order shape moments that can be used to generalise the KSB method to arbitrary order. Many independent shear estimators can then be formed for each object, using linear combinations of shapelet coefficients. These estimators can be treated separately, to improve their overall calibration; or combined in more sophisticated ways, to eliminate various instabilities and a calibration bias. We apply several methods to simulated astronomical images containing a known input shear, and demonstrate the dramatic improvement in shear recovery using shapelets. A complete IDL software package to perform image analysis and manipulation in shapelet space can be downloaded from www.astro.caltech.edu/~rjm/shapelets/.
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