  We investigate the properties of hybrid gravitational/hydrodynamical
simulations, examining both the numerics and the general physical properties of
gravitationally driven, hierarchical collapse in a mixed baryonic/dark matter
fluid. We demonstrate that, under certain restrictions, such simulations
converge with increasing resolution to a consistent solution. The dark matter
achieves convergence provided that the relevant scales dominating nonlinear
collapse are resolved. If the gas has a minimum temperature (as expected when
intergalactic gas is heated by photoionization due to the ultraviolet
background) and the corresponding Jeans mass is resolved, then the baryons also
converge. However, if there is no minimum baryonic collapse mass or if this
scale is not resolved, then the baryon results err in a systematic fashion. In
such a case, as resolution is increased the baryon distribution tends toward a
higher density, more tightly bound state. We attribute this to the fact that
under hierarchical structure formation on all scales there is always an earlier
generation of smaller scale collapses, causing shocks which irreversibly alter
the state of the baryon gas. In a simulation with finite resolution we miss
such earlier generation collapses, unless a physical scale is introduced below
which structure formation is suppressed in the baryons. We also find that the
baryon/dark matter ratio follows a characteristic pattern, such that collapsed
structures possess a baryon enriched core (enriched by factors of 2 or more
over the universal average) which is embedded within a dark matter halo, even
without accounting for radiative cooling of the gas. The dark matter is
unaffected by changing the baryon distribution (at least in the dark matter
dominated case investigated here).
