The Role of Baryons in Creating Statistically Significant Planes of
  Satellites around Milky Way-Mass Galaxies
  We investigate whether the inclusion of baryonic physics influences the
formation of thin, coherently rotating planes of satellites such as those seen
around the Milky Way and Andromeda. For four Milky Way-mass simulations, each
run both as dark matter-only and with baryons included, we are able to identify
a planar configuration that significantly maximizes the number of plane
satellite members. The maximum plane member satellites are consistently
different between the dark matter-only and baryonic versions of the same run
due to the fact that satellites are both more likely to be destroyed and to
infall later in the baryonic runs. Hence, studying satellite planes in dark
matter-only simulations is misleading, because they will be composed of
different satellite members than those that would exist if baryons were
included. Additionally, the destruction of satellites in the baryonic runs
leads to less radially concentrated satellite distributions, a result that is
critical to making planes that are statistically significant compared to a
random distribution. Since all planes pass through the centre of the galaxy, it
is much harder to create a plane from a random distribution if the satellites
have a low radial concentration. We identify Andromeda's low radial satellite
concentration as a key reason why the plane in Andromeda is highly significant.
Despite this, when co-rotation is considered, none of the satellite planes
identified for the simulated galaxies are as statistically significant as the
observed planes around the Milky Way and Andromeda, even in the baryonic runs.
