Evolution of Extragalactic Radio Sources

Abstract

I review the current paradigm for extragalactic radio sources including their classification, relationship to their host galaxies, their environments, their propagation, and their lifetimes. I emphasize recent progress in our understanding of radio source evolution and I discuss the current open questions. In spite of the many outstanding questions, there remains the following "working" paradigm. Massive BHs are present in many (all?) bright galaxies. Activity is triggered when gas reaches the central accretion disk - possibly with the assistance of an interaction. The type of resultant activity depends on the fueling rate and BH properties (Mass and Spin) which in turn may be related to the host galaxy and its immediate environment. The radio jets in the classical doubles power an over-pressured cocoon which propagates through the ISM/ICM in a roughly self-similar way. The GPS and CSS sources are likely to be the young progenitors of the powerful large-scale radio sources and if so can be used to constrain their evolution. Current constraints imply that sources evolve with roughly constant expansion speed and decline in radio power with linear size as P ∝ l^-0.5. Lifetimes of canonical powerful radio sources are in the range l0^6-8 yr (with the less powerful oncs living longer). Finally, activity may be repetitive.