Compact steep spectrum radio sources and the nuclear environment

Abstract

Compact steep Spectrum (CSS) radio sources occur in galaxies at redshifts greater than about 0.2. It has been speculated that these small double sources are either young radio sources which will grow into ‘‘standard’’ radio sources or that they are in fact older but intermittent, with more extended weak relic radiation, and that the intermittency may be due to ‘‘smothering’’ of the source by infall of a very dense ISM near the AGN nucleus. Calculations of the evolution of these objects will be shown, and these indicate that the near nuclear environment has an average number density of about 1.0 particle/cc within the inner few kpc. In addition these calculations indicate that these objects are probably ‘‘young’’ radio sources. ISM number densities much in excess of the above number produce small sources with spectra which do not agree with observations, and less dense nuclear regions cannot confine the sources long enough to provide the observed spectral index—linear size relation.