The Evolution of Compact Steep Spectrum Sources

Time-dependent numerical simulations of jets associated with compact steep spectrum (CSS) and possibly the gigahertz peaked spectrum (GPS) sources have been made. The goal is to determine if these objects can be permanently confined by a dense ISM in the core of an active galaxy. Propagation into both a homogeneous ISM with and without density gradients and a more realistic two-phase ISM, populated with cold, dense clouds has been calculated. In general, CSS sources of low and intermediate luminosity can be confined by an ISM of average density 10 times that of the Galaxy. Confinement of the highest luminosity sources requires an ISM of unrealistic density and total mass. The population as a whole can be confined if the jets are intrinsically more efficient, by factors of 10 or more, than is commonly assumed for "normal" radio sources. Stability of the interface between the dense ISM and the rarefied jet material is examined. Magnetic fields can provide stabilization against the Rayleigh-Taylor instability, but the more realistic two-phase ISM simulations show that stabilization is not an issue because no well-defined interface occurs. Subject headings galaxies: ISM - galaxies: jets - MHD - radio continuum: galaxies