Weak weak lensing: correcting weak shear measurements accurately for PSF anisotropy

Abstract

We have developed a new technique for weak lensing analysis, with which the effect of the point spread function (PSF) on small galaxy images can be corrected for accurately. Rather than relying on weighted second moments of detected images, which we show can leave residuals at the level of a percent in the shear, we directly fit (stacked or individual) galaxy images as PSF-convolved, sheared circular sources. We show by means of simulations that this technique is able to recover shears well below the percent level for a variety of PSF shapes, and that its noise properties are similar to existing methods.