GalSim: The modular galaxy image simulation toolkit

GALSIM is a collaborative, open-source project aimed at providing an image simulation tool of enduring benefit to the astronomi cal community. It provides a software library for generating images of astronomical objects such as stars and galaxies in a variety of ways, efficiently handling image transformations and opera tions such as convolution and rendering at high precision. We describe the GALSIM software and its capabilities, including necessary theore tical background. We demonstrate that the performance of GALSIM meets the stringent requirements of high precision image analysis applications such as weak gravitational lensing, fo r current datasets and for the Stage IV dark energy surveys of the Large Synoptic Survey Telescope, ESA’s Euclid mission, and NASA’s WFIRST-AFTAmission. The GALSIM project repository is public and includes the full code hist ory, all open and closed issues, installation instructions, documentation, and wi ki pages (including a Frequently Asked Questions section). The GALSIM repository can be found at https://github.com/GalSim-developers/GalSim.