Gas and stellar spiral structures in tidally perturbed disc galaxies
  Tidal interactions between disc galaxies and low mass companions are an
established method for generating galactic spiral features. In this work we
present a study of the structure and dynamics of spiral arms driven in
interactions between disc galaxies and perturbing companions in 3-D
N-body/smoothed hydrodynamical numerical simulations. Our specific aims are to
characterize any differences between structures formed in the gas and stars
from a purely hydrodynamical and gravitational perspective, and to find a
limiting case for spiral structure generation. Through analysis of a number of
different interacting cases, we find that there is very little difference
between arm morphology, pitch angles and pattern speeds between the two media.
The main differences are a minor offset between gas and stellar arms, clear
spurring features in gaseous arms, and different radial migration of material
in the stronger interacting cases. We investigate the minimum mass of a
companion required to drive spiral structure in a galactic disc, finding the
limiting spiral generation cases with companion masses of the order
$1\times10^9M_\odot$, equivalent to only 4% of the stellar disc mass, or 0.5%
of the total galactic mass of a Milky Way analogue.
