AGNS in clusters of galaxies and the bootes void

Abstract

Recent evidence suggests that about 30% of high power sources may be triggered by galaxy mergers (Heckman et al., 1986). However, for sources below the break in the radio luminosity function, galaxy radio emission has a variety of causes. The abundance of gas within a galaxy and the evolutionary state of a galaxy can apparently determine if a weak radio source will “turn-on”. This is often seen to be true from rich cluster sources to the Bootes void emission-line objects. External stimulation is not always required. However, there is a prominent subset of galaxies where interaction with companions has helped to generate a radio source. Such interaction appears to greatly enhance the probability that a galaxy will become active. Finally, the global environment seems to have little effect on generating radio galaxies. Weak sources are found to exist within rich clusters and cosmic voids. The exceptions are dominant galaxies that lie at the centers of clusters. These galaxies are 5 times more likely to be radio sources than typical ellipticals. The cooling flows in some clusters may help to stimulate the production of radio sources, but also suppress extended structure.