Hosts of powerful radio galaxies in the near-infrared: Implications for radio source evolution

By means of KPNO 2.1 m J-, H-, and K-band data on samples of gigahertz peaked spectrum (GPS, radio size <1 kpc), compact steep spectrum (CSS, 1-20 kpc), and 3CR classical doubles (>20 kpc), we have constructed mean broadband spectral energy distributions (SEDs) for each of the object classes and compared these with synthetic SEDs. The host galaxies of the compact and extended radio sources appear to have similar near-IR broadband SEDs, implying similar stellar populations and active galactic nuclei (AGNs). These SEDs are best fitted with a mean metallicity similar to solar and fairly old stellar populations implying formation redshifts of greater than or similar to 5. Redshift evolution of the sources is consistent with a passive evolutionary model. In addition, an extra IR component is needed that can be modeled by emission from dust at a temperature of 900-1300 K, perhaps produced by the putative obscuring torus. All of our results are consistent with the hypothesis that the GPS and CSS are the progenitors of the large-scale 3CR radio galaxies.