Active Galaxies and Clusters of Galaxies

摘要

X-ray observations of clusters of galaxies have shown that the entropy of the intracluster medium (ICM), is higher than that expected from gravitational processes. This is believed to be the result of nongravitational processes. We discuss the role of active galaxies in clusters in changing the entropy of the ICM. A central AGN can inject buoyant bubbles into the ICM, and heat it up by doing pdV work as they rise and expand. Energetic particles from AGN can also increase the entropy by coulomb interaction with the ICM, and this process can also explain the abundance of 6Li in halo metal poor stars. We then discuss the implications of a recent radio obser vation of four poor clusters with enhanced entropy. The upper limit on the emission at low frequency supports the pre-heating scenario in which ICM is heated before the assembly of galaxy cluster.