Clusters of Galaxies

Clusters of galaxies can be used as powerful cosmological probes with which to measure the fundamental properties of our Universe. In order to do this effectively, their masses must be measured. This is an observational challenge as clusters are dominated by dark matter, and we must estimate their masses from our observations of their luminous matter. By combining observations of the hot gas in clusters made with X-ray observatories (such as XMM and Chandra), with measurements of the Sunyaev-Zel'dovich effect (from experiments such as Planck, OCRA and AMiBA), measurements of the gravitational lensing effect of clusters, and the velocities of the galaxies within clusters (both using data from optical telescopes), we are attempting to measure the most accurate masses possible for a large number of galaxy clusters.

Distant galaxy clusters

We are also using X-ray observations to measure the temperatures of a sample of very distant galaxy clusters. The numbers of distant galaxy clusters of different temperatures and the evolution of this distribution relative to nearby clusters is very sensitive to underlying cosmological parameters. By comparing our observations with the predictions of different cosmological models we will gain new insight into the values of the parameters which describe the Universe.

Fig.1 shows the early stages of a merger between two massive subclusters (the two large, bright components in the centre) at a redshift of z=0.83. The cluster is part of a larger scale structure comprising at least two galaxy groups (fainter components towards the top right and bottom left). Many of the smaller sources in this image are active galactic nuclei in galaxies in the cluster, or in the foreground or background.

Advanced statistical modelling

We use advanced statistical techniques to model large populations of galaxy clusters to investigate the way that astrophysical processes have altered the relationships between their properties. Detailed analysis is required to model the biases that are introduced by the selection of clusters to study. We also work on developing new statistical techniques to detect galaxy clusters in large, multi-wavelength survey datasets.

Fig.1 X-ray observation of a distant galaxy cluster ClJ0152.7-1357
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