Radio-Loud AGN Heating in Elliptical Galaxies and Clusters

Summary

The role of radio-loud active galactic nuclei (AGN) in continually re-heating the cooling gas in the haloes surrounding elliptical galaxies, and in clusters of galaxies, is investigated. The prevalence of radio-loud AGN activity amongst elliptical galaxies is found to scale strongly with the mass of the central black hole (as M^1.6 _BH). Combining this result with estimates of the mechanical energy output of these radio sources, the time-averaged energy output associated with recurrent radio source activity is derived: for elliptical galaxies of all masses, this is shown to balance the radiative energy losses from the hot gas surrounding the galaxy. Recurrent radio-loud AGN activity may therefore provide a self-regulating feedback mechanism capable of controlling the rate of growth of galaxies. The prevalence of radio-loud AGN activity amongst brightest cluster galaxies, and other cluster members is also determined, to investigate AGN feedback in galaxy clusters. Unless the efficiency of converting AGN mechanical energy into heating increases by 2–3 orders of magnitude between groups and rich clusters, radio–mode heating will not balance radiative cooling in systems of all masses.