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

Abstract

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 travel through 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 most abundant in regions where the hot and cool gases first begin to mix or where the mixed gas has cooled significantly. The predicted column densities of high velocity Si iv and the predicted ratios of Si iv to C iv and O vi found on individual sightlines in our HVC simulations are in good agreement with observations of high velocity gas. Low velocity Si iv is also seen in the simulations, as a result of decelerated gas in the case of the HVC simulations and when looking along directions that pass perpendicular to the direction of motion in the TML simulations. The ratios of low velocity Si iv to C iv and O vi in the TML simulations are in good agreement with those recorded for Milky Way halo gas, while the ratio of Si iv to O vi from the decelerated gas in the HVC simulations is lower than that observed at normal velocity in the Milky Way halo. We attribute the shortfall of normal velocity Si iv to not having modeled the effects of photoionization and, following Henley et al., consider a composite model that includes decelerated HVC gas, supernova remnants, galactic fountain gas, and the effect of photoionization.

40 pages, 12 figures, and 6 tables

References in corpus (6)

• Time-Dependent Ionization in Radiatively Cooling Gas
• The COS/UVES Absorption Survey of the Magellanic Stream. III: Ionization, Total Mass, and Inflow Rate onto the Milky Way
• The Far Ultraviolet Spectroscopic Explorer Survey of OVI Absorption in the Disk of the Milky Way
• Numerical Study of Turbulent Mixing Layers with Non-Equilibrium Ionization Calculations
• Metallicity and Ionization in High Velocity Cloud Complex C
• High-Resolution Absorption Spectroscopy of Multi-phase, High-Metallicity Gas Associated with the Luminous Quasar HE 0226-4110

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• Self-ionizing galactic winds
• Mass, Morphing, Metallicities: The Evolution of Infalling High Velocity Clouds
• The warm Gaseous Disk and the Anisotropic Circumgalactic Medium of the Milky Way
• The Warm Gas in the MW: A Kinematical Model
• The Anatomy of a Turbulent Radiative Mixing Layer: Insights from an Analytic Model with Turbulent Conduction and Viscosity
• A hot gaseous galaxy halo candidate with Mg X absorption
• Coupling of Damped and Growing Modes in Unstable Shear Flow
• The high-velocity clouds above the disk of the outer Milky Way: misty precipitating gas in a region roiled by stellar streams
• The impact of magnetic fields on momentum transport and saturation of shear-flow instability by stable modes
• Solar-Metallicity Gas in the Extended Halo of a Galaxy at $z\sim 0.12$