Identifying true satellites of the Magellanic Clouds
  The hierarchical nature of LCDM suggests that the Magellanic Clouds must have
been surrounded by a number of satellites before their infall into the Milky
Way. Many of those satellites should still be in close proximity to the Clouds,
but some could have dispersed ahead/behind the Clouds along their Galactic
orbit. Either way, prior association with the Clouds results in strong
restrictions on the present-day positions and velocities of candidate
Magellanic satellites: they must lie close to the nearly-polar orbital plane of
the Magellanic stream, and their distances and radial velocities must follow
the latitude dependence expected for a tidal stream with the Clouds at
pericenter. We use a cosmological numerical simulation of the disruption of a
massive subhalo in a Milky Way-sized LCDM halo to test whether any of the 20
dwarfs recently-discovered in the DES, SMASH, Pan-STARRS, and ATLAS surveys are
truly associated with the Clouds. Of the 6 systems with kinematic data, only
Hydra II and Hor 1 have distances and radial velocities consistent with a
Magellanic origin. Of the remaining dwarfs, six (Hor 2, Eri 3, Ret 3, Tuc 4,
Tuc 5, and Phx 2) have positions and distances consistent with a Magellanic
origin, but kinematic data are needed to substantiate that possibility.
Conclusive evidence for association would require proper motions to constrain
the orbital angular momentum direction, which, for true Magellanic satellites,
must coincide with that of the Clouds. We use this result to predict radial
velocities and proper motions for all new dwarfs. Our results are relatively
insensitive to the assumption of first or second pericenter for the Clouds.
