Massive Black Holes in Quiescence

Joan M. Wrobel, National Radio Astronomy Observatory

Low-luminosity active galactic nuclei (LLAGNs) are often found in
nearby galaxies.  Energized by black holes with masses of 1e6 to 1e9
Solar masses, these LLAGNs are characterized by Eddington ratios in
the range 1e-3 to 1e-6.  Observations of these sub-Eddington accretors
imply that the massive black hole is surrounded by an inner
radiatively-inefficient accretion flow, a truncated outer thin disk,
and a jet or outflow. Guided by this framework, a few nearby galaxies
have been searched for the accretion signatures of massive black holes
in quiescence, that is, those with Eddington ratios below 1e-6. Search
results will be summarized and their implications will be explored.
The prospects for improved searches will also be examined.