The Extragalactic Gamma-Ray Background from Core Dominated Radio Galaxies

Recent radio surveys have discovered a large number of low luminosity core dominated radio galaxies that are much more abundant than those at higher luminosities. These objects will be too faint in \grays to be detected individually by {\it Fermi}. Nevertheless, they may contribute significantly to the unresolved extragalactic \gray background. We consider here the possible contribution of these core dominated radio galaxies to the diffuse extragalactic \gray background. Using published data available for all 45 of the radiogalaxies listed as detected counterparts in the {\it Fermi} FL8Y source list update to the 3FGL catalog, we have searched for radio maps which can resolve the core flux from the total source flux. Using high resolution radio maps we were able to obtain core fluxes for virtually every source. We then derived a relation between core radio flux and \gray flux that we extrapolated to sources with low radio luminosities that are known to be highly core dominated. We then employed a very recent determination of the luminosity function for core dominated radio galaxies in order to obtain the contribution of all possible \gray emitting radio galaxies to the unresolved extragalactic \gray background. We find this contribution to be a possibly non-negligible, 4\% - 18\% of the background.