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

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 gamma-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 gamma-ray undetected counterparts. In the gamma-ray band, FR0 radio galaxies exhibit spectral features similar to more common FR I and II radio galaxies, indicating a common gamma-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 gamma-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.

Automated summary

The latest addition to the jetted active galactic nuclei (AGN) family is the Fanaroff-Riley type 0 (FR0) radio galaxies, which have similar observational characteristics to FR I sources but lack the extended radio structures. By utilizing ongoing multiwavelength wide-field sky surveys, seven gamma-ray-emitting AGN have been identified as FR0 radio sources. The observed broadband properties of these objects are similar to their gamma-ray undetected counterparts, suggesting a common gamma-ray production mechanism and misaligned jets.