Inflow of the Broad-Line Region and the Fundamental Limitations of
  Reverberation Mapping
  The evidence from velocity-resolved reverberation mapping showing a net
infall of the broad-line region (BLR) of AGNs is reviewed. Different lines in
many objects at different epochs give a consistent picture of BLR motions. The
motions are dominated by virialized motion (rotation plus turbulence) with
significant net inflow. The BLR mass influx is sufficient to power the AGN. The
increasing blueshifting of lines with increasing ionization potential is a
consequence of scattering off infalling material. The high blueshiftings of the
UV lines in Narrow-Line Seyfert 1s are due to enhanced BLR inflow rates rather
than strong winds. Seemingly conflicting cases of apparent outflow
reverberation mapping signatures are a result of the breakdown of the
axial-symmetry assumption in reverberation mapping. There are several plausible
causes of this breakdown: high-energy variability tends to be intrinsically
anisotropic, regions of variability are necessarily located off-axis, and X-ray
observations reveal major changes in line-of-sight column densities close to
the black hole. Results from reverberation mapping campaigns dominated by a
single event need to be treated with caution.
