A search for $\gamma$-ray emission from a sample of local universe low-frequency selected radio galaxies

TL;DR

This study uses Fermi-LAT data to survey 78 local universe radio galaxies, detecting gamma-ray emission from known sources and finding potential new candidates, while assessing the likelihood of chance associations.

Contribution

It provides the first unbiased gamma-ray survey of a complete sample of low-redshift radio galaxies, identifying known sources and evaluating new potential gamma-ray emitters.

Findings

Detected gamma-ray emission from 4 known radio galaxies.

Identified 4 candidate radio galaxies with possible gamma-ray emission.

Calculated upper limits for non-detected sources.

Abstract

Radio galaxies are uncommon $\gamma$-ray emitters, and only low redshift radio galaxies are detected with Fermi-LAT. However, they offer potential insights into the emission mechanisms of active galaxies, particularly as the alignment of their jets with respect to the Earth means that, unlike blazars, their emission is not necessarily jet-dominated. We use Fermi-LAT data to perform an unbiased survey of 78 radio galaxies from the Bologna Complete Sample in order to search for new $\gamma$-ray-emitting radio galaxies. We observe statistically significant $\gamma$-ray emission from 4 of the 6 known Fermi-LAT detected radio galaxies included in this sample, and find some evidence for $\gamma$-ray emission spatially coincident with 4 previously undetected radio galaxies. As a large parameter space is searched, we calculate a probability distribution to compute the look-elsewhere effect. We find that these 4 spatially coincident sub-threshold $\gamma$-ray excesses are most likely a chance association, and are unlikely to be emission from the radio galaxies. Upper limits on flux are calculated for the radio galaxies from which no $\gamma$-ray emission is observed.