Relating the HI Gas Structure of Spiral Disks to Passing Satellites
  We extend the work of Chang & Chakrabarti (2011) to find simple scaling
relations between the density response of the gas disk of a spiral galaxy and
the pericenter distance and mass ratio of a perturbing satellite. From the
analysis of results from a test particle code, we obtained a simple scaling
relation for the density response due to a single satellite interacting with a
galactic disk, over a wide range of satellite masses and pericenter distances.
We have also explored the effects of multiple satellites on the galactic disk,
focusing on cases that are commonly found in cosmological simulations. Here, we
use orbits for the satellites that are drawn from cosmological simulations. For
these cases, we compare our approximate scaling relations to the density
response generated by satellites, and find that for two satellite interactions,
our scaling relations approximately recover the response of the galactic disk.
We have also examined the observed HI data in the outskirts of several spiral
galaxies from the THINGS sample and compared the observed perturbations to that
of cosmological simulations and our own scaling relations. While small
perturbations can be excited by satellites drawn from cosmological simulations,
we find that large perturbations (such as those that are seen in some THINGS
galaxies like M51) are not recovered by satellites drawn from cosmological
simulations that are similar to Milky Way galaxies.
