Evolution of Extragalactic Radio Sources

Abstract

I review the current paradigm for extragalactic radio sourcesincluding their classification, relationship to their host galaxies, theirenvironments, their propagation, and their lifetimes. I emphasize recentprogress in our understanding of radio source evolution and I discussthe current open questions. In spite of the many outstandingquestions, there remains the following "working" paradigm. MassiveBHs are present in many (all?) bright galaxies. Activity is triggeredwhen gas reaches the central accretion disk - possibly with the assistanceof an interaction. The type of resultant activity depends on thefueling rate and BH properties (Mass and Spin) which in turn may berelated to the host galaxy and its immediate environment. The radiojets in the classical doubles power an over-pressured cocoon whichpropagates through the ISM/ICM in a roughly self-similar way. TheGPS and CSS sources are likely to be the young progenitors of the powerfullarge-scale radio sources and if so can be used to constrain theirevolution. Current constraints imply that sources evolve with roughlyconstant expansion speed and decline in radio power with linear sizeas P ∝ l^-0.5. Lifetimes of canonical powerful radio sources are in therange l0^6-8 yr (with the less powerful oncs living longer). Finally,activity may be repetitive.