A Unified Framework for X-shaped Radio Galaxies

Abstract

We propose a radically different picture for X-shaped radio galaxies compared with existing models as transition objects between cold-mode accreting, low-spinning retrograde black holes and low-spinning prograde black holes. This model explains their smaller average black hole masses; their general aversion for cluster compared with isolated environments; the negligible difference in spectral index between primary and secondary jets, despite a time difference in their formation; their absence among the most powerful radio quasars and radio galaxies; and their connection to the elusive Fanaroff–Riley I quasar class, among others. The key to their formation is cold gas accretion onto Schwarzschild black holes.