Date: 19 Jan 2010
Satellite: XMM-Newton
Depicts: X-ray emission in a COSMOS group of galaxies
Copyright: ESA

This image shows how X-ray emission is used to determine which galaxy in a group of galaxies lies at the centre of the group. This is important in studies using weak gravitational lensing to measure the total mass (including dark matter) of groups and clusters of galaxies.

The colour (background) image was obtained with the Subaru telescope. Yellow contours show the X-ray emission as determined from XMM-Newton observations. The large galaxy at the centre of the image is the central galaxy of the group. This galaxy (COSMOS-XCL095951+014049) is at a redshift of 0.372 and is located at RA: 149.96413, Dec: 1.68033 (J2000).

The Cosmic Evolution Survey (COSMOS) is an astronomical survey designed to probe the formation and evolution of galaxies as a function of cosmic time (redshift) and large scale structure environment. The survey covers a 2 square degree equatorial field with imaging by mosey of the major space-based telescopes (including Hubble and XMM-Newton) and a number of ground-based telescopes.