Uncovering fossils of the distant Milky Way with UNIONS: NGC 5466 and
  its stellar stream
  We examine the spatial clustering of blue horizontal branch (BHB) stars from
the $\textit{u}$-band of the Canada-France Imaging Survey (CFIS, a component of
the Ultraviolet Near-Infrared Optical Northern Survey, or UNIONS). All major
groupings of stars are associated with previously known satellites, and among
these is NGC 5466, a distant (16 kpc) globular cluster. NGC 5466 reportedly
possesses a long stellar stream, although no individual members of the stream
have previously been identified. Using both BHBs and more numerous red giant
branch stars cross-matched to $\textit{Gaia}$ Data Release 2, we identify
extended tidal tails from NGC 5466 that are both spatially and kinematically
coherent. Interestingly, we find that this stream does not follow the same path
as the previous detection at large distances from the cluster. We trace the
stream across 31$^{\circ}$ of sky and show that it exhibits a very strong
distance gradient ranging from 10 $<$ R$_{helio}$ $<$ 30 kpc. We compare our
observations to simple dynamical models of the stream and find that they are
able to broadly reproduce the overall path and kinematics. The fact that NGC
5466 is so distant, traces a wide range of Galactic distances, has an
identified progenitor, and appears to have recently had an interaction with the
Galaxy's disk, makes it a unique test-case for dynamical modelling of the Milky
Way.
