Gas Disks and Supermassive Black Holes in Nearby Radio Galaxies

1.1 Radio galaxies
A radio galaxy can produce a jet-lobe, radio wavelength emitting, structure on mega-
parsec scales, emerging from a central engine that resides in an active region no more
than a few milli-parsecs in size. The radio emission is well understood to be from
synchrotron radiation, but the processes involved in fueling and collimating the ra-
dio jets are yet to be explained (Lynden-Bell, 2001). The energy that powers the
radio jets is typically believed to be produced during the accretion of material onto
a central supermassive black hole (e.g., Lynden-Bell, 1969). The formation of such
well organized large scale jet structures is some of the most compelling evidence for
the necessity of supermassive black holes as an ingredient in the makeup of a radio
galaxy (Rees, 1984).
Radio emission can be detected even from relatively quiescent galaxies, such
as the Milky Way, on the level of around 10 37 erg s −1 . Active galaxies (such as
Seyferts or starburst galaxies) radiate at around 10 37 erg s −1 , and radio galaxies (and
also quasars) extend this energy output range to beyond 10 45 erg s −1 (∼ 10 12 L⊙)
(Burke & Graham-Smith, 1997). An active galaxy central engine capable of releas-
ing ∼ 0.1Mfuelc 2 of infalling fuel as radiation would need to be fueled at a rate of
∼> 1 M⊙ yr −1 to maintain this luminosity.
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