Near IR Observations of Powerful Radio Galaxies

The Optical to mid IR band is critical to our understanding of the properties of the host galaxies and AGN in powerful radio galaxies. These wavelengths probe the stellar populations, the alignment effect, the bolometric luminosity of the AGN, and the circumnuclear obscuring torus. We have begun a program to determine the spectral energy distribution of a sample of powerful radio galaxies whose radio sources range in size from tens of pc to hundreds of kpc. These objects span the distribution of observed sizes and should consist of objects at all stages of evolution. The sample was constructed in such a way that we have roughly equal numbers of sources within each size class: Gigahertz peaked spectrum (GPS) (<1 kpc), compact steep spectrum (CSS) (between 1 and 20 kpc) and 3CR FR II radio galaxies (3CR) (> 20 kpc). Using our groundbased R,J,H and K-band we have are constructed a mean broadband SED for each of our subsamples and compared it with the synthetic SED constructed with the GISSEL96 code of Bruzual and Charlot. The GPS, CSS and 3CR have similar broadband spectra in the near IR, consistent with them having similar stellar populations and AGN. The SED is best fit with metallicity which is 20-40% of solar and fairly old stellar populations implying formation redshifts in the range 5-10. In addition, an extra IR component is needed which can be modeled by emission from dust at a temperature of 800-1200 K. If this is the correct interpretation, this may be produced by the putative obscuring torus.