Jeans Instability in a Tidally Disrupted Halo Satellite Galaxy
  We use a hybrid test particle/N-body simulation to integrate 4 million
massless test particle trajectories within a fully self-consistent 10^5
particle N-body simulation. The number of massless particles allows us to
resolve fine structure in the spatial distribution and phase space of a dwarf
galaxy as it is disrupted in the tidal field of a Milky Way type galaxy. The
tidal tails exhibit nearly periodic clumping or a smoke-like appearance. By
running simulations with different satellite particle mass, halo particle mass,
number of massive and massless particles and with and without a galaxy disk, we
have determined that the instabilities are not due to numerical noise,
amplification of structure in the halo, or shocking as the satellite passes
through the disk of the Galaxy. We measure Jeans wavelengths and growth
timescales in the tidal tail and show that the Jeans instability is a viable
explanation for the clumps. We find that the instability causes velocity
perturbations of order 10 km/s. Clumps in tidal tails present in the Milky Way
could be seen in stellar radial velocity surveys as well as number counts. We
find that the unstable wavelength growth is sensitive to the simulated mass of
dark matter halo particles. A simulation with a smoother halo exhibits colder
and thinner tidal tails with more closely spaced clumps than a simulation with
more massive dark matter halo particles. Heating by the halo particles
increases the Jeans wavelength in the tidal tail affecting substructure
development, suggesting an intricate connection between tidal tails and dark
matter halo substructure.
