X-Ray Surveys: WARPS - An X-ray survey of distant Clusters of Galaxies

A false colour XMM-Newton X-ray image of a distant cluster of galaxies caught in the act of formation. Within the circle are two major subclumps of emission from hot gas, a third, fainter (probably infalling) group to the left, several point-like sources, and a filamentary feature to the upper right. Infalling groups and gas along filaments are predicted by simulations of cluster formation.

Besides their component galaxies, clusters of galaxies contain a hot (50 million K) plasma emitting X-rays. By searching for resolved X-ray sources detected serendipitously in ROSAT X-ray images, we have been able to compile a sample of 150 clusters of galaxies which includes many very distant clusters. The cluster shown above, at a redshift of z=0.83, is among the most distant and massive X-ray clusters known. It has several components, probably in the process of merging. By comparing the properties of the distant clusters (such as space density, X-ray luminosity & temperature) with nearby clusters, we learn how structure in the Universe, exemplified by the clusters, has grown over a large fraction of the age of the Universe. Models predict that the rate of growth of structure on the large scales of clusters is particularly sensitive to the value of Omega, the mean density of mass in the Universe, and thus these observations can accurately measure Omega.

Ongoing observations with the XMM-Newton and Chandra X-ray Observatories and optical/NIR observations with UKIRT, Gemini and HST (to measure galaxy properties), are giving very detailed information on the formation and evolution of clusters and their constituent galaxies at high redshifts.

Researchers: Laurence Jones, Ben Maughan