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J.F. Wallin (George Mason University), K. Olson (Univ. of Chicago), A. Haque, S. Milder, J. Brugioni (George Mason University)
Most of our understanding of the gas dynamics in interacting galaxies relies on simulations which use Smoothed Particle Hydrodynamics (SPH). SPH simulations have been successful at reproducing many of the basic morphological and kinematic features seen in interacting systems. Artificial viscosity is used in SPH simulations to smooth the numerical ringing caused by shocks and to prevent interpenetration of streaming flows. Several forms of this general idea have evolved for simulations of interacting galaxies (Selhammer 1997; Hernquist & Katz 1989; Monaghan 1992), and a great deal of work has been done trying to create alternative forms of artificial viscosity for SPH (Watkins et.al. 1996; Balsara 1995; Morris & Monaghan 1997). Our studies of collisional ring show that the form and parameters used in artificial viscosity affect our conclusions about gas distribution and star formation resulting galaxy interactions. We will discuss these results, and address how these uncertainties might be removed from the next generation of numerical models.