The SAMI Galaxy Survey: A Range in S0 Properties Indicating Multiple
  Formation Pathways
  It has been proposed that S0 galaxies are either fading spirals or the result
of galaxy mergers. The relative contribution of each pathway, and the
environments in which they occur remains unknown. Here we investigate stellar
and gas kinematics of 219 S0s in the SAMI Survey to look for signs of multiple
formation pathways occurring across the full range of environments. We identify
a large range of rotational support in their stellar kinematics, which
correspond to ranges in their physical structure. We find that
pressure-supported S0s with $v/{\sigma}$ below 0.5 tend to be more compact and
feature misaligned stellar and gas components, suggesting an external origin
for their gas. We postulate that these S0s are consistent with being formed
through a merger process. Meanwhile, comparisons of ellipticity, stellar mass
and S\'ersic index distributions with spiral galaxies shows that the
rotationally supported S0s with $v/{\sigma}$ above 0.5 are more consistent with
a faded spiral origin. In addition, a simulated merger pathway involving a
compact elliptical and gas-rich satellite results in an S0 that lies within the
pressure-supported group. We conclude that two S0 formation pathways are
active, with mergers dominating in isolated galaxies and small groups, and the
faded spiral pathway being most prominent in large groups ($10^{13} < M_{halo}
< 10^{14}$).
