Sizing from the Smallest Scales: The Mass of the Milky Way
  As the Milky Way and its satellite system become more entrenched in near
field cosmology efforts, the need for an accurate mass estimate of the Milky
Way's dark matter halo is increasingly critical. With the second and early
third data releases of stellar proper motions from {\it Gaia}, several groups
calculated full $6$D phase-space information for the population of Milky Way
satellite galaxies. Utilizing these data in comparison to subhalo properties
drawn from the Phat ELVIS simulations, we constrain the Milky Way dark matter
halo mass to be $\sim 1-1.2\times10^{12}~\msun$. We find that the kinematics of
subhalos drawn from more- or less-massive hosts (i.e. $>1.2\times10^{12}~\msun$
or $<10^{12}~\msun$) are inconsistent, at the $3\sigma$ confidence level, with
the observed velocities of the Milky Way satellites. The preferred host halo
mass for the Milky Way is largely insensitive to the exclusion of systems
associated with the Large Magellanic Cloud, changes in galaxy formation
thresholds, and variations in observational completeness. As more Milky Way
satellites are discovered, their velocities (radial, tangential, and total)
plus Galactocentric distances will provide further insight into the mass of the
Milky Way dark matter halo.
