Improved Dynamical Constraints on the Masses of the Central Black Holes
  in Nearby Low-mass Early-type Galactic Nuclei And the First Black Hole
  Determination for NGC 205
  We improve the dynamical black hole (BH) mass estimates in three nearby
low-mass early-type galaxies--NGC 205, NGC 5102, and NGC 5206. We use new
\hst/STIS spectroscopy to fit the star formation histories of the nuclei in
these galaxies, and use these measurements to create local color--mass-to-light
ratio (\ml) relations. We then create new mass models from \hst~imaging and
combined with adaptive optics kinematics, we use Jeans dynamical models to
constrain their BH masses. The masses of the central BHs in NGC 5102 and NGC
5206 are both below one million solar masses and are consistent with our
previous estimates, $9.12_{-1.53}^{+1.84}\times10^5$\Msun~and
$6.31_{-2.74}^{+1.06}\times10^5$\Msun~(3$\sigma$ errors), respectively.
However, for NGC 205, the improved models suggest the presence of a BH for the
first time, with a best-fit mass of
$6.8_{-6.7}^{+95.6}\times10^3$\Msun~(3$\sigma$ errors). This is the least
massive central BH mass in a galaxy detected using any method. We discuss the
possible systematic errors of this measurement in detail. Using this BH mass,
the existing upper limits of both X-ray, and radio emissions in the nucleus of
NGC 205 suggest an accretion rate $\lesssim$$10^{-5}$ of the Eddington rate. We
also discuss the color--\mleff~relations in our nuclei and find that the slopes
of these vary significantly between nuclei. Nuclei with significant young
stellar populations have steeper color--\mleff~relations than some previously
published galaxy color--\mleff~relations.
