Disk Outflows and High-Luminosity True Type 2 AGN
  The absence of intrinsic broad line emission has been reported in a number of
active galactic nuclei (AGN), including some with high Eddington ratios. Such
"true type 2 AGN" are inherent to the disk-wind scenario for the broad line
region: Broad line emission requires a minimal column density, implying a
minimal outflow rate and thus a minimal accretion rate. Here we perform a
detailed analysis of the consequences of mass conservation in the process of
accretion through a central disk. The resulting constraints on luminosity are
consistent with all the cases where claimed detections of true type 2 AGN pass
stringent criteria, and predict that intrinsic broad line emission can
disappear at luminosities as high as about 4x$10^{46}$ erg s$^{-1}$ and any
Eddington ratio, though more detections can be expected at Eddington ratios
below about 1%. Our results are applicable to every disk outflow model,
whatever its details and whether clumpy or smooth, irrespective of the wind
structure and its underlying dynamics. While other factors, such as changes in
spectral energy distribution or covering factor, can affect the intensities of
broad emission lines, within this scenario they can only produce true type 2
AGN of higher luminosity then those prescribed by mass conservation.
