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Session 95 - X-Ray Galaxies and Clusters.
Oral session, Wednesday, January 17
La Condesa, Hilton
The central regions of clusters of galaxies are extremely active environments containing X-ray emitting cooling gas, very large cD galaxies, radio galaxies, optical emission line filaments, and regions of blue continuum light due to young stars and/or scattered radiation from an AGN. We have analyzed recent ROSAT HRI X-ray images of a number of cooling flow clusters. The primary focus of this study is the structure of the X-ray emission in the central parts of the clusters and its connection with other components of the systems. We find that the central X-ray emission structures in these clusters are generally complex. For example, in the Hercules cluster (A2151), the X-ray emission divides into two components which corresponds to two gravitational potential wells in the central subcluster. In this cluster, one finds evidence for a cooling flow, ram pressure stripping of interstellar gas from galaxies, subcluster mergers, and the interaction between a radio source and the ambient gas.
We particularly studied a sample of cooling flow clusters with central radio sources. Morphologically, they seem to divide into two groups. Most of the radio sources have well-defined radio lobes with strong radio jets. They are highly polarized, but have high Faraday rotations due to the ambient cooling flow gas. The radio lobes are usually in weak regions of X-ray emission, and have comparable pressures between the X-ray gas and the radio plasma. This anticorrelation between the radio and X-ray suggest that the radio jets in these sources inflate distinct radio lobes, which displace but are confined by the ambient X-ray gas. In a few cases, the radio sources are quite amorphous, with little evidence for strong radio jets. They are unpolarized, probably by differential Faraday rotation along the line of sight through the sources. The radio sources are correlated with the X-ray emissions but have a much weak radio pressure than the X-ray gas pressure in the region. These suggest that the radio and X-ray emitting plasmas in these amorphous sources are mixed.
Program listing for Wednesday