Galaxy Systems: Groups



Contours of soft X-ray emission are shown superimposed on an optical plate of the galaxy group HCG97. This compact group contains only five galaxies (marked with crosses) in a very close configuration. The X-ray emission arises from hot (~10 million K) gas trapped in the gravitational potential well of the group. As can be seen, this gas extends well beyond the optical confines of the group, and it can be used to infer the existence of a large amount of dark matter, which is similarly extended.

The majority of galaxies in the Universe, including our own, appear to reside in groups. Most galaxy groups are "loose groups", in which the galaxies are separated by distances of several hundred kiloparsecs, however "compact groups" such as HCG97 are much easier to identify optically.

The study of groups and their galaxies is a special interest of the group at Birmingham. Groups are especially important since:

Click below for information about some of our main projects involving galaxy groups.

Group evolution Hot gas in groups Fossil groups

Researchers: Trevor Ponman, Laurence Jones, Ale Terlevich, Steve Helsdon, Ed Lloyd-Davies, Ewan O'Sullivan, David Acreman, Alastair Sanderson and John Osmond.

This page was written by Trevor Ponman, and last updated on