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abstract
Extragalactic observations of neutral hydrogen frequently are presented as contours of column density in position-velocity space. Models are needed to interpret these results, and we have calculated two-dimensional numerical hydrodynamic models of a gaseous disk with differing supernovae rates. For each of the models considered, H I position-velocity diagrams are computed, which are compared to similar 21 cm observations of nearby galaxies. The diagrams from the simulations reproduce the qualitative features in the observations, such as holes in the H I, but the dispersion in velocity is only about half that observed for the Galactic energy injection rate. In addition, we do not see evidence of a large amount of high velocity ($>$ 75 km s$^{-1}$) H I, although in the simulations with the highest energy injection rate (4 $\times$ Galactic) some H I is occasionally seen at velocities near or above 50 km s$^{-1}$. Both of these results are most likely caused by numerical viscosity, which may be alleviated in the future by higher resolution simulations.
