Abstract

We use a large, statistically very well characterised X-ray flux-limited sample of galaxy clusters to study the large-scale structure of the Universe out to redshifts of ~0.4. Testing cosmological models by means of the cluster X-ray luminosity function we obtain tight constraints on the matter density and amplitude parameter of the density fluctuation power spectrum. We find some tension in the resulting density fluctuation amplitude with the prediction from the Planck results in the frame of the standard Lambda-CDM cosmological model. The tension implies a less pronounced fluctuation amplitude of nearby large-scale structure a compared to the predictions. The results can be reconciled, however, by for example introducing massive neutrinos.

We also use the cluster sample to study superclusters and the matter distribution in the local Universe. One of the findings of this research is a locally underdense region in the Southern Galactic Cap region, with interesting consequences for local measurements of cosmological parameters, like the Hubble constant.