Constraints on Evolutionary Properties of GHz Peaked Spectrum Galaxies
  We have used the available samples of Gigahertz Peaked Spectrum (GPS) galaxies to investigate their evolution properties in the framework of the ``youth'' scenario. Care was taken to properly allow for the different selection criteria used to define the samples. We find that the observed redshift and peak frequency distributions can be satisfactorily accounted for in terms of simple luminosity evolution of individual sources, along the lines discussed by Fanti et al. (1995) and Begelman (1996, 1999), although the derived parameter values have large uncertainties due to ambiguities in the selection of GPS sources and to the incompleteness of redshift measurements. However the simplest self-similar model, whereby the evolution is controlled only by the radial profile of the density of the ambient medium is not good enough and one additional parameter needs to be introduced. The fit requires a decrease of the emitted power and of the peak luminosity with source age or with decreasing peak frequency, at variance with the Snellen et al. (2000) model. On the other hand, our analysis confirms the rather flat slope of the luminosity function, found by Snellen et al. (2000) who also report indications of a high luminosity break, not required by the data sets we have used. Our results suggest that the GPS galaxies are the precursors of extended radio sources with luminosities below the break of the luminosity function. No cosmological evolution of the GPS galaxy population is required by presently available data. 
S. Tinti and G. De Zotti