A detailed mass-calibration study of intermediate and high-redshift galaxy clusters with Gravitational Lensing and X-ray techniques

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The first precise determination of the fundamental cosmological parameters with high precision has been undertaken with studies of the Cosmic Microwave Background (CMB). Going beyond those large-scale, primordial relics of the Big Bang, we can test cosmological models and determine the fundamental ingredients, the dynamics and the geometry of our Universe also with galaxy clusters as non-linear tracers of the Cosmic Web. They represent the largest dark matter haloes in our Universe and they formed only relatively recently. Therefore, cosmological studies based on galaxy clusters are complementary to CMB results and they allow important consistency checks. To use galaxy clusters for cosmological studies has two obvious prerequisites: First, we need large, well defined cluster samples with a profound understanding of the underlying selection functions. Second, we need to be able to precisely determine and to calibrate the masses of our cluster sample. Our group is leading several observational opportunities whose scientific objective is the thorough mass analysis of large samples of galaxy clusters at different epochs. This proposal focuses on the second prerequisite mentioned above: The precise calibration of cluster masses. The primary goal is to perform a precise mass calibration study on a sample of five medium-to-high redshift (z = 0.3 − 0.55) galaxy clusters. For all clusters we have high-quality optical space-based mosaic data from ACS@HST and supplementary multi-colour observations from the ground for gravitational lensing studies. Independent, and complementary mass estimates will come from X-ray studies using already existing Chandra and XMM data. The combined X-ray and lensing study will allow us to gain profound insight in the mass distribution of these systems. Our group can build on significant expertise which we gained in a first pilot program on the most luminous X-ray cluster RXJ1347−1145.