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We present predictions of the Si iv ions in turbulent mixing layers (TMLs)between hot and cool gas and in cool high-velocity clouds (HVCs) that travelthrough a hot halo, complementing the C iv, N v, and O vi predictions in Kwak &Shelton, Kwak et al., and Henley et al. We find that the Si iv ions are mostabundant in regions where the hot and cool gases first begin to mix or wherethe mixed gas has cooled significantly. The predicted column densities of highvelocity Si iv and the predicted ratios of Si iv to C iv and O vi found onindividual sightlines in our HVC simulations are in good agreement withobservations of high velocity gas. Low velocity Si iv is also seen in thesimulations, as a result of decelerated gas in the case of the HVC simulationsand when looking along directions that pass perpendicular to the direction ofmotion in the TML simulations. The ratios of low velocity Si iv to C iv and Ovi in the TML simulations are in good agreement with those recorded for MilkyWay halo gas, while the ratio of Si iv to O vi from the decelerated gas in theHVC simulations is lower than that observed at normal velocity in the Milky Wayhalo. We attribute the shortfall of normal velocity Si iv to not having modeledthe effects of photoionization and, following Henley et al., consider acomposite model that includes decelerated HVC gas, supernova remnants, galacticfountain gas, and the effect of photoionization.

Si iv Column Densities Predicted from Non-Equilibrium Ionization Simulations of Turbulent Mixing Layers and High-Velocity Clouds