Automatic detection of gravitational arcs in wide-area survey data, comparison of the observed and the theoretically expected arc abundance

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The abundance of distant galaxies which are strongly distorted by the gravitational lensing effect of galaxy clusters, so-called arcs, is a potentially very powerful measure for non-linear cosmological structure formation at the highest mass scales. Up to now, it is observationally poorly known because of the small area surveyed and statistical inhomogeneity of the sample. To improve this situation, we have developed the fast “arcfinder” software for the automatic detection of arcs in large images. Equipped with an efficient filter for spurious detections, the arcfinder is now ready to be applied to existing and upcoming wide-area survey data, in particular the CFHTLS-wide and the Pan-STARRS PS 1 surveys. We are proposing a project in which the arcfinder will be applied to these and possible other data sets. Calibration runs will be carried out to determine the efficiency and the selection function of the arc detections. Existing software will be used to model the mass distributions of the lenses producing the arcs detected. In parallel, we shall improve theoretical predictions of the arc abundance with an emphasis on understanding the systematic uncertainties involved and the magnitude of the sample variance. We expect this project to result in a substantially improved understanding of whether the abundance of arcs is in fact in conflict with the predictions of the standard cosmological model, as many studies suggest.