AGN feedback from a radio galaxy perspective
The relationship between black hole mass and bulge mass (Magorrian et al. 1998; Gebhardt et al. 2000a) indicates a symbiotic relationship between the formation of supermassive black holes and galaxy formation. Silk and Rees (1998) indicated how an isotropic wind from a black hole may interact with the infalling gas in a forming galaxy to provide a natural relationship between black hole mass and bulge mass. Saxton et al. (2005) also showed that jets propagating through an inhomogeneous interstellar medium generate an energy-driven, more or less spherical bubble, different from the bipolar structure that is usually associated with classical radio galaxies. Thus, from our viewpoint, when we consider the interaction between jets and the interstellar medium we naturally think of gigahertz peak spectrum (GPS) and compact steep spectrum (CSS) radio galaxies as well as high redshift radio galaxies. These sources appear to be radio galaxies in the early stages of their evolution in which there is abundant evidence for strong jet–ISM interaction in the form of shock-excited emission lines and anomalous gas velocities. Given that jet power and momentum can be isotropically distributed by an inhomogeneous medium, an important issue to address is the detailed interaction between clouds and outflows in such a medium. The nature of this interaction and in particular the momentum imparted to the gas surrounding the active nucleus is going to be quite different from that envisaged by Silk and Rees (1998) and many other papers since.