Radiatively Inefficient Accretion in Nearby Galaxies
  We use new central stellar velocity dispersions and nuclear X-ray and Halpha
luminosities for the Palomar survey of nearby galaxies to investigate the
distribution of nuclear bolometric luminosities and Eddington ratios for their
central black holes (BHs). This information helps to constrain the nature of
their accretion flows and the physical drivers that control the spectral
diversity of nearby active galactic nuclei. The characteristic values of the
bolometric luminosities and Eddington ratios, which span over 7-8 orders of
magnitude, from L_bol < 10^37 to 3 X 10^44 erg/s and L_bol/L_Edd ~ 10^-9 to
10^-1, vary systematically with nuclear spectral classification, increasing
along the sequence absorption-line nuclei --> transition objects --> LINERs -->
Seyferts. The Eddington ratio also increases from early-type to late-type
galaxies. We show that the very modest accretion rates inferred from the
nuclear luminosities can be readily supplied through local mass loss from
evolved stars and Bondi accretion of hot gas, without appealing to additional
fueling mechanisms such as angular momentum transport on larger scales. Indeed,
we argue that the fuel reservoir generated by local processes should produce
far more active nuclei than is actually observed. This generic
luminosity-deficit problem suggests that the radiative efficiency in these
systems is much less than the canonical value of 0.1 for traditional optically
thick, geometrically thin accretion disks. The observed values of L_bol/L_Edd,
all substantially below unity, further support the hypothesis that massive BHs
in most nearby galaxies reside in a low or quiescent state, sustained by
accretion through a radiatively inefficient mode.
