Constraints on evolutionary properties of GHz Peaked Spectrum galaxies

Abstract

\n We have used the available samples of Gigahertz Peaked\nSpectrum (GPS) galaxies to investigate their evolution properties\nin the framework of the “youth” scenario. Care was taken to\nproperly allow for the different selection criteria used to define\nthe samples. We find that the observed redshift and peak frequency\ndistributions can be satisfactorily accounted for in terms of\nsimple luminosity evolution of individual sources, along the lines\ndiscussed by Fanti et al. (1995, A&A, 302, 317) and Begelman (1996, in Proc. Cygnus A, Study of Radio Galaxy; 1999, in Proc. of KNAW Colloq.),\nalthough the derived parameter values have large uncertainties due\nto ambiguities in the selection of GPS sources and to the\nincompleteness of redshift measurements. However the simplest\nself-similar model, whereby the evolution is controlled only by\nthe radial profile of the density of the ambient medium is not\ngood enough and one additional parameter needs to be introduced.\nThe fit requires a decrease of the emitted power and of the peak\nluminosity with source age or with decreasing peak frequency, at\nvariance with the Snellen et al. (2000, MNRAS, 319, 445) model. On the other hand,\nour analysis confirms the rather flat slope of the luminosity\nfunction, found by Snellen et al. (2000) who also report\nindications of a high luminosity break, not required by the data\nsets we have used. Our results suggest that the GPS galaxies are\nthe precursors of extended radio sources with luminosities below\nthe break of the luminosity function. No cosmological evolution of\nthe GPS galaxy population is required by presently available data.\n \n \n