Feeding the central engine in giant radio galaxies

Abstract

Giant radio galaxies are thought to be massive ellipticals powered by accretion of interstellar matter onto a supermassive black hole. Interactions with gas rich galaxies may provide the interstellar matter to feed the active galactic nucleus (AGN). To power radio lobes that extend up to distances of hundreds of kiloparsecs, gas has to be funneled from kiloparsec size scales down to the AGN at rates of ~1 Mo yr^-1 during >10^8 years. Therefore, large and massive quasi-stable structures of gas and dust should exist in the deep interior of the giant elliptical hosts of double lobe radio galaxies. Recent mid-infrared observations with ISO revealed for the first time a bisymmetric spiral structure with the dimensions of a small galaxy at the centre of Centaurus A (Mirabel et al. 1999, A&A 341, 667). The spiral was formed out of the tidal debris of accreted gas-rich object(s) and has a dust morphology that is remarkably similar to that found in barred spiral galaxies. The observations of the closest AGN to Earth suggest that the dusty hosts of giant radio galaxies like CenA, are "symbiotic" galaxies composed of a barred spiral inside an elliptical, where the bar serves to funnel gas toward the AGN.