The case for inflow of the broad-line region of active galactic nuclei
  The high-ionization lines of the broad-line region (BLR) of thermal active
galactic nuclei (AGNs) show blueshifts of a few hundred km/s to several
thousand km/sec with respect to the low-ionization lines. This has long been
thought to be due to the high-ionization lines of the BLR arising in a wind of
which the far side of the outflow is blocked from our view by the accretion
disc. Evidence for and against the disc-wind model is discussed. The biggest
problem for the model is that velocity-resolved reverberation mapping
repeatedly fails to show the expected kinematic signature of outflow of the
BLR. The disc-wind model also cannot readily reproduce the red side of the line
profiles of high-ionization lines. The rapidly falling density in an outflow
makes it difficult to obtain high equivalent widths. We point out a number of
major problems with associating the BLR with the outflows producing broad
absorption lines. An explanation which avoids all these problems and satisfies
the constraints of both the line profiles and velocity-resolved
reverberation-mapping is a model in which the blueshifting is due to scattering
off material spiraling inwards with an inflow velocity of half the velocity of
the blueshifting. We discuss how recent reverberation mapping results are
consistent with the scattering-plus-inflow model but do not support a disc-wind
model. We propose that the anti-correlation of the apparent redshifting of
H$\beta$ with the blueshifting of CIV is a consequence of contamination of the
red wings of H$\beta$ by the broad wings of [O III].
