Hunting Gamma-Ray-emitting FR0 Radio Galaxies in Wide-field Sky Surveys

Abstract

The latest entry in the jetted active galactic nuclei (AGN) family is the Fanaroff–Riley type 0 (FR0) radio galaxies. They share several observational characteristics, e.g., nuclear emission and host galaxy morphology, with FR I sources; however, they lack extended, kiloparsec-scale radio structures, which are the defining features of canonical FR I and II sources. Here we report the identification of seven γ-ray-emitting AGN as FR0 radio sources by utilizing the high-quality observations delivered by ongoing multiwavelength wide-field sky surveys, e.g., Very Large Array Sky Survey. The broadband observational properties of these objects are found to be similar to their γ-ray undetected counterparts. In the γ-ray band, FR0 radio galaxies exhibit spectral features similar to more common FR I and II radio galaxies, indicating a common γ-ray production mechanism and the presence of misaligned jets. Although the parsec-scale radio structure of FR0s generally exhibits a wide range, with about half having emission on opposite sides of the core, the γ-ray-detected FR0s tend to have dominant cores with core-jet structures. We conclude that dedicated, high-resolution observations are needed to unravel the origin of relativistic jets in this enigmatic class of faint yet numerous population of compact radio sources.

Characterizing the γ-Ray Emission from FR0 Radio Galaxies

“…Motivated by the similarity of the core emission between the FR0 population and the famous FRI M87 (e.g., Boughelilba & Reimer 2023), our modeling work uses a jet inclination angle similar to that of M87. Still, larger viewing angles for the FR0s are possible, as implied by Pannikkote et al (2023). A larger viewing angle decreases the Doppler factor for a given bulk Lorentz factor.…”

“…Moreover, FR0s represent the dominant population of radio sources in the local Universe (redshift of z < 0.05), having a number density roughly 5 times higher than FRIs. Because of their ubiquity, it is imperative to study and characterize the broadband electromagnetic radiation from FR0 galaxies, including their high-energy γ-ray emission (Baldi et al 2019b;Baldi 2023;Boughelilba & Reimer 2023;Pannikkote et al 2023).…”