The Size of the Broad Line Region in M84 (NGC 4374)
  M84 is a giant elliptical galaxy located in the Virgo cluster. Prior imaging
with the Hubble Space Telescope (HST) revealed a small, highly inclined,
nuclear ionized gas disk, the kinematics of which indicate the presence of a
0.4 -1.5 billion solar mass black hole. Two prominent radio jets emerge
perpendicular to the nuclear ionized gas disk terminating in large radio lobes
that extend beyond the visible galaxy. Plausible kinematic models are used to
constrain the size of the broad line region (BLR) in M84 by modeling the shape
of the broad H-alpha emission line profile. The analysis indicates that the
emitting region is large with an outer radius between ~ 7 and 9 pc, depending
on whether the kinematic model is represented by a spherically symmetric inflow
or a Keplerian disk. The inferred size makes the BLR in M84 the largest yet to
be measured. The fact that the BLR in M84 is so large may explain why the AGN
is unable to sustain the ionization seen there. Thus, the BLR in M84 is not
simply that of a scaled down quasar.
