Groups: Evolution

Galaxy groups are evolving structures, and this evolving environment can have  a profound effect on the evolution of the galaxies they contain. For example, the high densities and low relative velocities found within evolved groups, make them the most likely places to find galaxies merging. The evolution of galaxy groups is not well understood, and at Birmingham, we are attempting to improve this situation in a number of ways:-

  • Groups are observed to have very diverse properties, and it is very likely that these are related to their evolutionary status. For example, the Local Group in which our own Galaxy is located, is a low density group, dominated by spiral galaxies, which has yet to finish collapsing out of the expanding Hubble flow. It is very different from typical X-ray bright groups. To understand the relationship between the properties and evolution of groups, we are engaged in two major multiwavelength surveys of group properties:
    • The XI (XMM-IMACS) project - a collaboration between Birmingham and the Carnegie Institute in Pasadena to study the galaxy dynamics and hot intergalactic gas in a statistical sample of optically selected groups
  • As part of the XMM-LSS project, we are assembling and studying an X-ray selected sample of galaxy groups at a redshift z~0.3-0.5, whose properties we will compare with local groups, to probe evolutionary differences directly.
  • Fossil groups are believed to be the end-point of group evolution, when all the major galaxies have merged into a single large central elliptical galaxy. we have an active programme investigating the properties of these important cosmic structures.
  • Comparison of our group observations with the results of cosmological simulations are being carried out as part of the Millennium simulation project , in collaboration with members of the VIRGO consortium.

Researchers: Trevor Ponman, Somak Raychaudhury, Abdulmonem Alshino, Alastair Sanderson, Ali Dariush, Ria Johnson, Smriti Mahajan, Nathan Slack, Graham Smith


A strongly evolving group - this X-ray image of the galaxy group centred on the galaxy NGC 5171, taken with the XMM-Newton observatory, shows a highly disturbed distribution of hot gas. This results from a merger between two galaxy groups which is currently underway in this system.