GalactICS with Gas
  We present a new version of the GalactICS code that can generate
self-consistent equilibrium galaxy models with a two-component stellar disc and
a gas disc as well as a centrally-concentrated bulge and extended dark halo.
The models can serve as initial conditions for simulations of isolated galaxies
that include both hydrodynamics and collisionless dynamics. We test the code by
evolving a pair of simple gas disc-halo models, which differ only in the
initial temperature of the gas component. The models are similar to the ones
considered in the Wang et al. except that here, the halo is live whereas they
included the halo as a fixed potential. We find that the basic structural
properties of the models, such as the rotation curve and surface density
profiles, are well-preserved over 1.5 Gyr. We also construct a Milky Way model
that includes thin and thick stellar disc components, a gas disc, a bulge, and
a dark halo. Bar formation occurs in all disc-like components at about 1 Gyr.
The bar is strongest in the thin disc while the gas disc contains the most
prominent spiral features. The length of the bar in our model is comparable to
what has been inferred for the Galactic bar.
