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Description
We use new precision measurements of black hole (BH) masses from water megamaser disks to investigate scaling relations between macroscopic galaxy properties and supermassive BH mass. The megamaser-derived BH masses span 10^6^-10^8^M_{sun}_, while all the galaxy properties that we examine (including total stellar mass, central mass density, and central velocity dispersion) lie within a narrower range. Thus, no galaxy property correlates tightly with M_BH_ in ~L* spiral galaxies as traced by megamaser disks. Of them all, stellar velocity dispersion provides the tightest relation, but at fixed {sigma}_*_ the mean megamaser M_BH_ are offset by -0.6+/-0.1dex relative to early-type galaxies. Spiral galaxies with non-maser dynamical BH masses do not appear to show this offset. At low mass, we do not yet know the full distribution of BH mass at fixed galaxy property; the non-maser dynamical measurements may miss the low-mass end of the BH distribution due to an inability to resolve their spheres of influence and/or megamasers may preferentially occur in lower-mass BHs.
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