Intracluster Medium
Intracluster Medium
| Topics: |  Intergalactic Medium Galaxies |
Properties of the Intracluster Medium
The intracluster medium (ICM) is a hot ionized gas which fills the space between the galaxies in Galaxy Clusters (See Figure 1). The ICM is composed of gas which fell into the cluster and gas which has been removed from cluster galaxies. The gas expelled from galaxies has been enriched by elements produced inside stars, and the resulting metalicity of the ICM is about 1/3 that of our sun. The gas is removed from the galaxies either by galaxy scale winds powered by supernovae or by stripping due to the pressure of the ICM as the galaxies move through the cluster. About 2/3 of the baryonic matter in a cluster of galaxies is in the hot gas in the ICM and the rest is in the galaxies. The density is in the range 10-3 to 10-4 particles/cm3, and the temperature is roughly tenmillion degrees. This is hot enough that the gas emits X-rays via thermal Bremstrahlung radiation. There is also line emission due to the heavy elements in the gas.
Figure 1. Comparison of X-ray and optical images of the Cluster of Galaxies Abell 2029. The X-ray emission from the ICM is much smoother than the light from the galaxies. (Source/Credit: Chandra.)
Cooling Flows
Figure 2. Chandra X-ray image of the central region of the Perseus cluster of galaxies. The image shows bubbles and shock waves driven by the central Radio Galaxy. (Source/Credit: NASA/CXC/IoA/A.Fabian et al.)
In the central parts of the cluster, the gas is able to radiate enough of its energy that it should cool and drop out of the hot phase at rates ofabout 10-100 times the mass of our sun per year.It appears that much of the energy radiated by the gas is replaced by some form of energy input into the gas. Currently it is thought that the energy input is due to Radio Galaxies produced by the massive central galaxy.
(See Figure 2).
Preview Image
This optical and X-ray composite image shows Abell 2029, one of 26 galaxy clusters studied by Chandra, located one billion light years away. Visit "Chandra Discovery Sheds Light on Dark Energy" for full size version. Credit: Optical: National Optical Astronomy Observatory/Kitt Peak, X-ray: NASA/Chandra X-ray Center/IoA.
Citation
O'Dea, Christopher, Ph.D. (Contributing Author); Bernard Haisch (Topic Editor). 2008. "Intracluster Medium." In: Encyclopedia of the Cosmos. Eds. Bernard Haisch and Joakim F. Lindblom (Redwood City, CA: Digital Universe Foundation). [First published December 16, 2007].
<http://www.cosmosportal.org/articles/view/135766/>
Contact Us
Send to a Friend
Comments
There are no comments.