On the Disappearance of the Broad-Line Region in Low-Luminosity Agns
  The disk-wind scenario for the broad-line region (BLR) and toroidal
obscuration in active galactic nuclei predicts the disappearance of the BLR at
low luminosities. In accordance with the model predictions, data from a nearly
complete sample of nearby AGNs show that the BLR disappears at luminosities
lower than $5\times\E{39} (M/10^7\Mo)^{2/3}$ erg s$^{-1)$, where $M$ is the
black hole mass. The radiative efficiency of accretion onto the black hole is
$\la \E{-3}$ for these sources, indicating that their accretion is
advection-dominated.
