On the evolution of young radio-loud AGN

This paper describes an investigation of the early evolution of extragalacticradio sources using samples of faint and bright Gigahertz Peaked Spectrum (GPS)and Compact Steep Spectrum (CSS) radio galaxies. Correlations found betweentheir peak frequency, peak flux density and angular size provide strongevidence that synchrotron self absorption is the cause of the spectralturnovers, and indicate that young radio sources evolve in a self-similar way.In addition, the data seem to suggest that the sources are in equipartitionwhile they evolve. If GPS sources evolve to large size radio sources, theirredshift dependent birth-functions should be the same. Therefore, since thelifetimes of radio sources are thought to be short compared to the Hubble time,the observed difference in redshift distribution between GPS and large sizesources must be due to a difference in slope of their luminosity functions. Weargue that this slope is strongly affected by the luminosity evolution of theindividual sources. A scenario for the luminosity evolution is proposed inwhich GPS sources increase in luminosity and large scale radio sources decreasein luminosity with time. This evolution scenario is expected for a ram-pressureconfined radio source in a surrounding medium with a King profile density. Inthe inner parts of the King profile, the density of the medium is constant andthe radio source builds up its luminosity, but after it grows large enough thedensity of th e surrounding medium declines and the luminosity of the radiosource decreases. A comparison of the local luminosity function (LLF) of GPSgalaxies with that of extended sources is a good test for this evolutionscenario [abridged]