A SELF-SIMILAR MODEL FOR EXTRAGALACTIC RADIO-SOURCES

An analytical model for extragalactic radio sources with pressure-conf ined jets is presented. We show that the properties of the bow shock a nd of the gas surrounding these objects force the sources to grow in a self-similar way provided the density in the external atmosphere fall s less steeply than 1/d(2). Results from observations and numerical si mulations are used to develop a self-consistent model for the large-sc ale structure of FRII objects. The jets in these sources are shown to be stable against turbulence for the observed properties of FRIIs and the divide between FRI and FRII objects in jet power is reproduced. Th e overall dynamics of a source are derived as a function of time and d epend on the external density, the jet power and the scaleheight of th e external atmosphere. Derived dynamical ages are consistent with obse rved spectral ages.