IM3SHAPE: A maximum-likelihood galaxy shear measurement code for cosmic gravitational lensing

Understand

We present and describe im3shape, a new publicly available galaxy shape measurement code for weak gravitational lensing shear.

• im3shape performs a maximum likelihood fit of a bulge-plus-disc galaxy model to noisy images, incorporating an applied point spread function.
• We detail challenges faced and choices made in its design and implementation, and then discuss various limitations that affect this and other maximum likelihood methods.
• We assess the bias arising from fitting an incorrect galaxy model using simple noise-free images and find that it should not be a concern for current cosmic shear surveys.