Shapelets: A New Method to Measure Galaxy Shapes

Abstract

We present a new approach to measure the shapes of galaxies, a fundamental task in observational astronomy. This approach is based on the decomposition of a galaxy image into a series of orthogonal basis functions, or `shapelets'. Our choice of basis functions, namely the Gauss-Hermite series, has a number of remarkable properties under distortions, convolutions and noise, which makes them particularly well suited for astrophysical applications. In particular, we describe how they can be used to measure the shear induced by weak gravitational lensing, with the precision required for upcoming surveys. We also show how shapelets can be used to reconstruct images from interferometric observations. Other application of shapelets, such as image compression, PSF deconvolution, de-projection and the study of galaxy morphology, are also briefly discussed.