Special Cosmology Seminar, Gayoung Chon "Cosmological studies with the REFLEX cluster survey"

Tue, Sep 1, 2015, 2:00 pm to 3:30 pm
Joseph Henry Room
We use a large, statistically well characterised X-ray flux-limited sample of galaxy clusters in the southern hemisphere to study the large-scale structure of the Universe and to probe cosmology out to redshifts of ~ 0.4. We study X-ray superclusters constructed with a strict definition such that they will collapse in the future given by a density threshold or infall velocity criterion. We show with N-body simulations that these two criteria are practically equivalent. With the cluster mass function we obtain tight constraints on the matter density and amplitude parameter of the density fluctuation power spectrum. There is some tension between our results and those from PLANCK in the frame of the standard Lambda-CDM cosmological model. The results can be reconciled by, for example, introducing massive neutrinos, or much larger hydrostatic mass bias. We also use the cluster sample to study the matter distribution in the local Universe in a cosmographical fashion. One of the findings is a locally underdense region in the Southern Galactic Cap region, with interesting consequences for local measurements of cosmological parameters, like the Hubble constant.