Fermi Gamma-ray Imaging of a Radio Galaxy

TL;DR

This paper reports the first resolved gamma-ray imaging of a radio galaxy lobes by Fermi, revealing significant emission from the lobes and providing insights into their magnetic fields and cosmic photon fields.

Contribution

It presents the first gamma-ray images of radio galaxy lobes, offering new constraints on their magnetic fields and particle content, and introduces a method to study cosmic relic photon fields.

Findings

Gamma-ray emission from radio galaxy lobes is significant and resolvable.

Lobe emission is mainly inverse Compton scattering of CMB and EBL.

Provides constraints on magnetic fields and particle energies in lobes.

Abstract

The Fermi Gamma-ray Space Telescope has detected the gamma-ray glow emanating from the giant radio lobes of the radio galaxy Centaurus A. The resolved gamma-ray image shows the lobes clearly separated from the central active source. In contrast to all other active galaxies detected so far in high-energy gamma-rays, the lobe flux constitutes a considerable portion (>1/2) of the total source emission. The gamma-ray emission from the lobes is interpreted as inverse Compton scattered relic radiation from the cosmic microwave background (CMB), with additional contribution at higher energies from the infrared-to-optical extragalactic background light (EBL). These measurements provide gamma-ray constraints on the magnetic field and particle energy content in radio galaxy lobes, and a promising method to probe the cosmic relic photon fields.