Radio Morphology of Gamma-ray Sources -- II. Giant Radio Galaxies

TL;DR

This study systematically identified 16 gamma-ray emitting giant radio galaxies using radio surveys and Fermi-LAT data, revealing their properties and suggesting similar gamma-ray emission mechanisms to other misaligned AGN.

Contribution

First systematic search of gamma-ray emission in giant radio galaxies using multiple radio surveys and Fermi-LAT data, identifying 8 new gamma-ray emitting GRGs.

Findings

16 gamma-ray emitting GRGs identified, 8 are new detections.

Gamma-ray properties similar to misaligned AGN, indicating similar emission mechanisms.

Differences in core dominance suggest smaller viewing angles for gamma-ray detected GRGs.

Abstract

Giant radio sources, including galaxies and quasars (hereafter GRGs), are active galactic nuclei (AGN) hosting relativistic jets with source sizes exceeding the 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 gamma-ray emitters. Since GRGs 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 gamma-ray emission. We have carried out a systematic search of gamma-ray emitting GRGs using sensitive low-resolution radio surveys, such as by Low Frequency Array, NRAO VLA Sky Survey, and Rapid ASKAP Continuum Survey, and considering the fourth data release of the fourth Fermi-Large Area Telescope gamma-ray source (4FGL-DR4) catalog. By carefully inspecting the radio maps of all AGN included in the 4FGL-DR4 catalog, we have identified 16 gamma-ray emitting GRGs, including 8 of them being reported as GRGs for the first time. Some of their observed parameters, e.g., core dominance, appeared to differ from that found for the non-gamma-ray detected GRG population, possibly due to the relatively small viewing angle of the gamma-ray emitting jet. The observed gamma-ray properties of these objects were found to be similar to non-GRG gamma-ray emitting misaligned AGN. We conclude that the origin of the gamma-ray emission could be similar in both source populations.