Shear-selection of galaxy clusters in the KIDS survey.

Gravitational lensing is an excellent tool for studying the mass distribution in the Universe, because it does not make assumptions about the nature or the dynamical state of the gravitating matter. In particular, lensing does not discriminate between the luminous and dark matter, and is thus a unique tool for studying the latter which otherwise evades observations. This aspect is very important for an analysis of the massive structures in the Universe, since dark matter dominates their state and evolutio n, starting from largest known objects, superclusters of galaxies, down to individual galaxies. Gravitational lensing manifests itself in distortions of the images of background galaxies, whose light bundles get sheared when passing through the tidal gra vitational field of an intervening mass concentration. This effect is very small and only statistically measurable on a large number of background galaxies; it is also referred to as weak lensing. Very deep exposures taken under excellent observing condit ions are essential to measure this effect. Great care has to be taken in the data reduction process to avoid the introduction of systematic effects. In order to exploit weak lensing as a cosmological probe, a very large observational data base is needed. The Kilo Degree Survey (KIDS) is one such observational campaign, led by the international Astrowise Consortium. The duty station of my PhD would be at Bonn University, one out of the five Astrowise Centres. Therein, I will work together with the gravita tional lensing group of Peter Schneider, establishing a large sample of shear-selected galaxy clusters. Since I already gained substantial experience with data reduction and weak lensing during my Master Thesis, I am optimally prepared for this PhD. The international context of this challenging project and its status at the very front of modern observational cosmology make it an optimal starting point for my future work as a scientist.