Inferring the Galactic potential with Gaia and friends: synergies with
  other surveys
  In the coming decade the Gaia satellite will precisely measure the positions
and velocities of millions of stars in the Galactic halo, including stars in
many tidal streams. These streams, the products of hierarchical accretion of
satellite galaxies by the Milky Way (MW), can be used to infer the Galactic
gravitational potential thanks to their initial compactness in phase space.
Plans for observations to extend Gaia's radial velocity (RV) measurements to
faint stars, and to determine precise distances to RR Lyrae (RRLe) in streams,
would further extend the power of Gaia's kinematic catalog to characterize the
MW's potential at large Galactocentric distances. In this work I explore the
impact of these extra data on the ability to fit the potential using the method
of action clustering, which statistically maximizes the information content
(clumpiness) of the action space of tidal streams, eliminating the need to
determine stream membership for individual stars. Using a mock halo in a toy
spherical potential, updated post-launch error models for Gaia, and estimates
for RV and distance errors for the tracers to be followed up, I show that
combining either form of additional information with the Gaia catalog greatly
reduces the bias in determining the scale radius and total mass of the Galaxy,
compared to the use of Gaia data alone.
