We study all the main components of galaxy clusters: the hot gas (which emits X-rays), the dark matter (which is inferred from its gravitational effects) and the galaxies.

Current research areas include:

• Merging clusters - we are investigating the effects of merging on clusters through a programme of XMM observations, and also studying the effects of merging on star formation, through multi object spectroscopy of cluster galaxies.
• Distribution of matter - 3-dimensional models of the distribution of gas within clusters are fitted to X-ray spectral images from the ROSAT, ASCA and Chandra observatories, to determine the distribution of gas density and temperature, and hence the dark matter distribution.
• Birmingham-CfA cluster scaling project - assembling X-ray derived results for the distribution of gas and dark matter in clusters, together with optical profiles, this project is studying the way in which the properties of virialised systems scale from individual elliptical galaxies up to rich clusters.
• Cosmological constraints from clusters - important constraints on the fundamental properties of the Universe can be derived from the baryon fractions and mass-to-light ratios we derive for nearby clusters. We are also using samples of high redshift clusters from the WARPS survey, followed up with deep Chandra and XMM studies, to constrain key cosmological parameters.
• Colour magnitude relations for cluster galaxies - the CMR can be used as a powerful tool to explore the environmental dependence of galaxy evolution in clusters compared to less rich environments.
• Ages and metallicities of cluster galaxies - Spectroscopic techniques to measure the ages and metallicities of cluster galaxies confirm that the CMR traces a sequence in galaxy metallicity, while departures from the CMR are related to differences in galaxy age.
• Dynamics of galaxies in clusters - the dynamics of galaxy orbits within clusters can be investigated by combining observations of galaxy redshifts as a function of radius, with the cluster mass models derived by other means, for example x-ray observations or gravitational lensing. The anisotropy of the galaxy orbits is related to the processes of cluster formation and evolution.
• Galaxy wakes - hydrodynamical modelling of the process of formation of wakes as galaxies move through the cluster environment will be coupled with observations from ROSAT, Chandra and XMM. This can constrain the properties and the dynamics of cluster galaxies.
• Hydrodynamic simulations of clusters - we have developed a 1-dimensional hydrocode which follows the evolution of the gas within a deepening cluster potential well, allowing for the effects of galaxy winds, or of preheating of the gas.

Researchers: Alastair Sanderson, Trevor Ponman, Somak Raychaudhury, Laurence Jones

The image on the left shows an X-ray image of the rich galaxy cluster Abell 2142, taken with the Chandra Observatory. This cluster is clearly elongated, and is believed to be the result of a recent merger between two clusters which have fallen together along the long axis. The high resolution of Chandra shows the existence of two sharp edges in the X-ray emission, to the northwest (top right), and also to the south (bottom) of the bright central region. These "steps" in the X-ray brightness can be seen more clearly as a bunching of the contours in the smoothed image on the right. They may be the leading edges of the two clusters which have merged.