Constraining Black Hole Spin based on the Absence of Lense-Thirring
  Precession of Megamaser Clumps
  We make use of the absence of Lense-Thirring precession of the innermost
megamaser clumps around black holes in order to place upper limits on the spin
amplitude of seven black holes at the center of megamaser galaxies: NGC 4258,
NGC 2273, UGC 3789, NGC 3393, NGC 5495, NGC 5765b, and UGC 6093. The
constraints are derived by requiring that the associated precession time-scale
be longer than the age of the megamaser clumps, in order to preserve the
single-plane geometry of the megamasers.
