Cosmology and Cosmography with X-ray Galaxy Clusters  / Dr Hans Boehringer (Max Planck Institute for Extraterrestrial Physics)

Galaxy clusters as the largest clearly defined astronomical
objects are powerful probes to characterise the large-scale
structure of our Universe. In this way observations of the
galaxy cluster population constitutes one of the few reliable
probes that allow us to test cosmological models.
Based on our large redshift survey of galaxy clusters detected
in X-rays with the ROSAT satellite we obtain constraints of
cosmological parameters in particular the mean matter density
of the Universe and the amplitude parameter of the large-scale
density fluctuations. In the talk these results will be discussed
in the light of the general status of characterising the cosmological
model that describes our Universe.
We find in particular some tension between our results and those
obtained through observations of the cosmic microwave background
observed by Planck, if the data are interpretated within the
standard Lambda-CMD model. This apparent discrepancy may hint
at the influence of massive neutrinos allowing us to put
constraints on the neutrino masses. We also use the cluster
sample to study the matter distribution in the local Universe
in a cosmographical fashion. One of the findings of this research
is a locally underdense region in the Southern Sky, with interesting
consequences for local measurements of the Hubble constant.