Implications of the Milky Way travel velocity for dynamical mass
  estimates of the Local Group
  The total mass of the Local Group (LG) is a fundamental quantity that enables
interpreting the orbits of its constituent galaxies and placing the LG in a
cosmological context. One of the few methods that allows inferring the total
mass directly is the "Timing Argument," which models the relative orbit of the
Milky Way (MW) and M31. However, the MW itself is not in equilibrium, a
byproduct of its merger history and the recent pericentric passage of the
LMC/SMC. As a result, recent work has found that the MW disk is moving with a
lower bound "travel velocity" of $\sim 32~{\rm km}~{\rm s}^{-1}$ with respect
to the outer stellar halo (Petersen & Pe\~{n}arrubia 2021), thus biasing past
Timing Argument measurements that do not account for this motion. We measure
the total LG mass using a Timing Argument model that incorporates this measured
travel velocity of the MW disk using several different compilations of recent
kinematic measurements of M31. We find that incorporating the measured travel
velocity lowers the inferred LG mass by 10-20% compared to a static MW halo,
and find an updated total mass of either $4.0^{+0.5}_{-0.3}\times 10^{12}\rm
M_{\odot}$ or $4.5^{+0.8}_{-0.6}\times 10^{12}\rm M_{\odot}$ depending on the
adopted dataset. Measurements of the travel velocity with more distant tracers
could yield even larger values, which would further decrease the inferred LG
mass. Therefore, the newly measured travel velocity directly implies a lower LG
mass than from a model with a static MW halo and must be considered in future
dynamical studies of the Local Volume.
