FR0 Radio Galaxies and Their Place in the Radio Morphology Classification

Abstract

So-called FR0 radio galaxies have recently emerged as a family of active galaxies with all the same properties as FRI radio galaxies except for their ratio of core to total emission, which is about 30 times higher than that of FRI sources. We show how their properties fit within the gap paradigm as low, prograde, spinning black holes whose progenitors are powerful FRII quasars that transitioned rapidly from the cold mode into advection-dominated accretion over a few million years. The prediction is that if sufficient fuel exists, FR0 radio galaxies will evolve into full-fledged FRI radio galaxies and the observational dearth of FRI radio galaxies compared to FR0s at low redshift tells us about the supply of gas in the low-redshift FR0s. Given the model prescription, this 5–1 FR0 to FRI ratio implies that at low redshift, the FRII quasar class of active galaxies struggles to fuel its black hole beyond 1.3 times its original mass. In addition to this, we illustrate model prescriptions for the black hole mass, black hole spin, redshift, and environment distribution for FR0 radio galaxies by fitting them within a paradigm that views them as a continuous class of active galaxies that are sandwiched between FRII quasars and FRI radio galaxies.