How to Detect Inclined Water Maser Disks (and Possibly Measure Black
  Hole Masses)
  We describe a method to identify inclined water maser disks orbiting massive
black holes and to potentially use them to measure black hole masses. Due to
the geometry of maser amplification pathways, the minority of water maser disks
are observable: only those viewed nearly edge-on have been identified,
suggesting that an order of magnitude additional maser disks exist. We suggest
that inward-propagating masers will be gravitationally deflected by the central
black hole, thereby scattering water maser emission out of the disk plane and
enabling detection. The signature of an inclined water maser disk would be
narrow masers near the systemic velocity that appear to emit from the black
hole position, as identified by the radio continuum core. To explore this
possibility, we present high resolution (0.07"-0.17") Very Large Array line and
continuum observations of 13 galaxies with narrow water maser emission and show
that three are good inclined disk candidates (five remain ambiguous). In the
best case, for CGCG 120$-$039, we show that the maser and continuum emission
are coincident to within $3.5\pm1.4$ pc ($6.7\pm2.7$ milliarcsec). Subsequent
very long baseline interferometric maps can confirm candidate inclined disks
and have the potential to show maser rings or arcs that provide a direct
measurement of black hole mass, although the mass precision will rely on
knowledge of the size of the maser disk.
