Improved Dynamical Constraints on the Mass of the central Black Hole in
  NGC 404
  We explore the nucleus of the nearby 10$^9M_{\odot}$~early-type galaxy
(ETGs), NGC~404, using Hubble Space Telescope (HST)/STIS spectroscopy and WFC3
imaging. We first present evidence for nuclear variability in UV, optical, and
infrared filters over a time period of 15~years. This variability adds to the
already substantial evidence for an accreting black hole at the center of
NGC~404. We then redetermine the dynamical black hole mass in NGC~404 including
modeling of the nuclear stellar populations. We combine HST/STIS spectroscopy
with WFC3 images to create a local color-$M/L$~relation derived from stellar
population modeling of the STIS data. We then use this to create a mass model
for the nuclear region. We use Jeans modeling to fit this mass model to
adaptive optics (AO) stellar kinematic observations from Gemini/NIFS. From our
stellar dynamical modeling, we find a 3$\sigma$ upper limit on the black hole
mass of $1.5\times10^5M_{\odot}$. Given the accretion evidence for a black
hole, this upper limit makes NGC~404 the lowest mass central black hole with
dynamical mass constraints. We find that the kinematics of H$_2$ emission line
gas show evidence for non-gravitational motions preventing the use of gas
dynamical modeling to constrain the black hole mass. Our stellar population
modeling also reveals that the central, counter-rotating region of the nuclear
cluster is dominated by $\sim$1~Gyr old populations.
