Research: Galaxy Clusters & Superclusters
Clusters of galaxies are the most massive objects (typically 1015 times the mass of the Sun) in the known universe, and well established probes of cosmology, dating back to Zwicky and Smith's seminal observations of the Coma and Virgo clusters in the 1930s. Like all cosmological probes, the astrophysics of galaxy clusters must be well understood in order to derive robust constraints on cosmology. Galaxy cluster research is therefore a challenging and exciting field, that is relevant to many of the big open questions of astrophysics and cosmology, for example: what is the nature of dark matter and dark energy that dominate the mass-energy content of the universe? how does the energy injected into clusters by cluster-cluster mergers and AGN influence their internal structure and global properties?
In addition to the dark matter that dominates their gravitational potential, clusters of galaxies possess a hot gaseous atmosphere, and host a significant population of galaxies. In Birmingham we use a wide range of observing facilities to probe the physical distribution and properties of these components of clusters. Key areas of expertise include:
- High resolution optical imaging (e.g. with Subaru and HST) to measure the gravitational lensing signal from clusters, and thus to measure the distribution of dark matter in clusters.
- X-ray observations with Chandra and XMM-Newton, aiming to measure the thermodynamics of the intracluster gas, specifically the temperature, entropy, and metallicity structure of the gas.
- Infrared observations, most recently with Herschel, to identify star-forming galaxies in clusters, and constrain the physical processes responsible for triggering and quenching star formation in cluster galaxies.
- Low frequency radio observations of synchrotron emission from relativstic electrons in "radio halos" and "radio relics", with GMRT and LOFAR.
A particular strength of our programme is the close collaboration between colleagues who work on each of these areas. For example, measuring the scaling relations between galaxy cluster mass (obtained from lensing observations) and the X-ray properties of clusters is a very active area of research. (Also see our cosmology page.)
Much of our research is performed as part of large international collaborations. For example, the Local Cluster Substructure Survey (LoCuSS), the Ultimate XMM Extragalactic Survey (XXL), the Arizona Cluster Redshift Survey (ACReS), the Representative XMM-Newton Cluster Structure Survey (REXCESS). We also collaborate closely with colleagues in the Sunyaev-Zeldovich Array (SZA, latterly part of CARMA), Massive Cluster Survey (MACS), and Herschel Lens Survey (HLS) teams. Our efforts will also turn increasingly towards cluster science with Euclid as launch approaches.
Our work on galaxy clusters is led by Dr Graham Smith (lensing, cosmology, LoCuSS, XXL, Euclid), Prof. Trevor Ponman (X-rays, astrophysics, XXL), and Dr Somak Raychaudhury (radio, superclusters, galaxies).
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