Radio morphology of gamma-ray sources. II. giant radio galaxies

Abstract

Giant radio sources, including galaxies and quasars (hereafter GRSs), are active galactic nuclei (AGN) hosting relativistic jets with source sizes exceeding a projected length of 0.7 Mpc. They are crucial to understanding the evolution of radio sources and their interaction with the surrounding environment. Some of these enigmatic objects, e.g., NGC 315, have also been reported as γ-ray emitters. Since GRSs are thought to be aligned close to the plane of the sky, they are invaluable targets to explore the radiative mechanisms responsible for the observed γ-ray emission. We have carried out a systematic search of γ-ray-emitting GRSs using sensitive low-resolution radio surveys, such as by the Low Frequency Array, NRAO Very Large Array Sky Survey, and Rapid ASKAP Continuum Survey, and considering the fourth data release of the fourth Fermi Large Area Telescope γ-ray source (4FGL-DR4) catalog. By carefully inspecting the radio maps of all AGN included in the 4FGL-DR4 catalog, we have identified 16 γ-ray-emitting GRSs, including eight that are being reported as GRSs for the first time. Some of their observed parameters, e.g., core dominance, appeared to differ from those found for the non-γ-ray detected GRS population, possibly due to the relatively small viewing angle of the γ-ray-emitting jet. The observed γ-ray properties of these objects were found to be similar to those of non-GRS γ-ray-emitting misaligned AGN. We conclude that the origin of the γ-ray emission could be similar in both source populations.