Characterization and dynamics of the peculiar stream Jhelum, A tentative
  role for the Sagittarius dwarf galaxy
  Stellar streams are a promising tool to study the Milky Way's dark matter
subhalo population, as interactions with subhalos could produce substructure in
streams. However, other possible causes for substructure first need to be well
understood. Here we study the kinematics and the unusual morphology of the
stellar stream Jhelum. Using a combination of ground-based photometry and Gaia
EDR3 astrometry we characterize the morphology of Jhelum. We combine this new
data with radial velocities from the literature to perform orbit integrations
of the stream in static Galactic potentials. We also explore N-body models in
the presence of large perturbers to explain some of the kinematic and
morphological features observed. The new data reveals a previously unreported
tertiary component in the stream, as well as several gaps and a kink-like
feature in its narrow component. We find that for a range of realistic Galactic
potentials, no single orbit is able to reproduce Jhelum's radial velocity data
entirely. A generic property of the orbital solutions is that they share a
similar orbital plane to Sagittarius and this leads to repeated encounters with
the stream. Using N-body simulations that include a massive Sagittarius, we
show that these encounters are able to reproduce the narrow and broad
components in Jhelum, as well as create a tertiary component in some cases. We
also find evidence that such encounters can result in an apparent increase in
the velocity dispersion of the stream by a factor up to ~ 5 due to overlapping
narrow and broad components. Our findings suggest that the Jhelum stream is
even more complex than once thought, however its morphology and kinematics can
be relatively easily explained via the interactions with Sagittarius. In this
scenario, the formation of Jhelum's narrow and broad components occurs
naturally, yet some of the smaller gap-like features remain to be explained.
