The dynamics of the broad-line region in NGC 3227
  Archival Hubble Space Telescope (HST) observations of the Seyfert 1 nucleus
of NGC 3227 obtained with the Space Telescope Imaging Spectrograph (STIS) are
re-examined in order to constrain a viable photoionization model for the
broad-line region (BLR). The results imply that the BLR is a partially ionized,
dust-free, spherical shell that is collapsing, supersonically, at the free-fall
velocity due to its proximity to a supermassive black hole. The BLR is
ionization bounded at the outer radius, coincident with the dust reverberation
radius, and transforms into an X-ray emitting plasma inside the Balmer
reverberation radius as the central UV--X-ray source is approached. Only 40
M_Sun of Hydrogen are required to explain the Balmer emission line luminosity,
but it is compressed by gravity into a column measuring 5.5 x 10^24 atoms/cm^2.
Assuming radiatively inefficient accretion, the X-ray luminosity requires ~
10^-2 M_sun/yr. However, the mass inflow rate required to explain the
luminosity of the broad H-alpha emission line is ~1 M_sun/yr. The very large
disparity between these two estimates indicates that 99% of the inflowing gas
must be re-directed into an outflow, and on a very short timescale
corresponding to ~40 years. Alternatively, the radiative efficiency of the
inflow has been overestimated, or the X-ray luminosity has been underestimated;
a distinct possibility if the BLR is indeed Compton thick.
