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The results of numerical hydrodynamical modeling of galaxy collisions involving gas-rich disks, like the Cartwheel ring galaxy, will be presented. These simulations are calculated in three dimensions using a Smoothed Particle Hydrodynamics (SPH) algorithm with rigid gravitational potentials for the companion galaxy and the primary halo, but with local self-gravity calculated within the disk. Also included are simple models of heating in dense regions (i.e. as a result of star formation activity) and radiative cooling, allowing a continuous range of thermal phases to develop in the gas. In the case of direct symmetric collisions, the hot gas is concentrated in the star-forming ring, but it is intermixed with warm and cold gas, in projection. Cool gas dominates in the rarefaction behind the ring. In off-center collisions, large azimuthal variations develop in the distribution of hot and cold gas within in the ring. In all collisional cases gas heated in a ring wave is pushed to significantly greater heights above the disk than those obtained from disk warping in isothermal simulations. Subsequently this gas cools, both radiatively, and by adiabatic expansion. Wave-induced gravitational instability, which can lead to clump and spoke formation in isothermal disks, is partially inhibited by the heating and vertical expansion. The timescale for the gas to cool and relax to the central plane is sufficiently long in the present models that gas compression, and star formation are reduced in the second ring wave, in contrast to the predictions of some earlier models.
