Realistic simulations of gravitational lensing by galaxy clusters: extracting arc parameters from mock DUNE images

Aims. We present a newly developed code that allows simulations of optical observations of galaxy fields with a variety of instruments. The code incorporates gravitational lensing effects and is targeted at simulating lensing by galaxy clusters. Our goal is to create the tools required for comparing theoretical expectations with observations to better understand of how observational noise affects lensing applications such as mass estimates, studies of the internal properties of galaxy clusters and arc statistics. Methods. Starting from a set of input parameters, characterizing both the instruments and the observational conditions, the simulator provides a virtual observation of a patch of the sky. It includes several sources of noise such as photon-noise, sky background, seeing, and instrumental noise. Ray tracing through simulated mass distributions accounts for gravitational lensing. Source morphologies are realistically simulated based on shapelet decompositions of galaxy images retrieved from the GOODS-ACS archive. According to their morphological class, spectral-energy-distributions are assigned to the source galaxies to reproduce observations of each galaxy in arbitrary photometric bands. Results. We illustrate our techniques showing virtual observations of a galaxy-cluster core as it would be observed with the space telescope DUNE, which was recently proposed to ESA within its "Cosmic vision" program. We analyze the simulated images using methods applicable to real observations and measure the properties of gravitational arcs. In particular, we focus on the determination of their length, width, and curvature radius. Conclusions. We find that arc properties strongly depend on several properties of the sources. In particular, our results show that compact, faint, or low surface-brightness galaxies that are barely detectable are more easily distorted as arcs with large length-to-width ratios. We conclude that realistic lensing simulations can be obtained with the method proposed here. They will be essential for evaluating and improving the analysis techniques currently used for cosmological interpretations of cluster lensing.