An Ultra Fast Image Generator (UFig) for wide-field astronomy

Simulated wide-field images are becoming an important part of observational astronomy, either to prepare for new surveys or to test measurement methods. In order to efficiently explore vast parameter spaces, the computational speed of simulation codes is a central requirement to their implementation. We introduce the Ultra Fast Image Generator (UFig) which aims to bring wide-field imaging simulations to the current limits of computational capabilities. We achieve this goal through: (1) models of galaxies, stars and observational conditions, which, while simple, capture the key features necessary for realistic simulations, and (2) state-of-the-art computational and implementation optimizations. We present the performances of UFig and show that it is faster than existing public simulation codes by several orders of magnitude. It allows us to produce images more quickly than SExtractor needs to analyze them. For instance, it can simulate a typical 0.25 deg^2 Subaru SuprimeCam image (10k x 8k pixels) with a 5-sigma limiting magnitude of R=26 in 30 seconds on a laptop, yielding an average simulation time for a galaxy of 30 microseconds. This code is complementary to end-to-end simulation codes and can be used as a fast, central component of observational methods relying on simulations.