Simulating Groups and the IntraGroup Medium: The Surprisingly Complex
  and Rich Middle Ground Between Clusters and Galaxies
  Galaxy groups are more than an intermediate scale between clusters and halos
hosting individual galaxies, they are crucial laboratories capable of testing a
range of astrophysics from how galaxies form and evolve to large scale
structure (LSS) statistics for cosmology. Cosmological hydrodynamic simulations
of groups on various scales offer an unparalleled testing ground for
astrophysical theories. Widely used cosmological simulations with ~(100 Mpc)^3
volumes contain statistical samples of groups that provide important tests of
galaxy evolution influenced by environmental processes. Larger volumes capable
of reproducing LSS while following the redistribution of baryons by cooling and
feedback are essential tools necessary to constrain cosmological parameters.
Higher resolution simulations can currently model satellite interactions, the
processing of cool (T~10^4 K) multi-phase gas, and non-thermal physics
including turbulence, magnetic fields, and cosmic ray transport. We review
simulation results regarding the gas and stellar contents of groups, cooling
flows and the relation to the central galaxy, the formation and processing of
multi-phase gas, satellite interactions with the intragroup medium, and the
impact of groups for cosmological parameter estimation. Cosmological
simulations provide evolutionarily consistent predictions of these
observationally difficult-to-define objects, and have untapped potential to
accurately model their gaseous, stellar, and dark matter distributions.
