Cooling Galactic Fountain Gas

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Session 114 -- Multi-Phase Interstellar Medium
Display presentation, Saturday, January 15, 9:30-6:45, Salons I/II Room (Crystal Gateway)

[114.04] Cooling Galactic Fountain Gas

R.A.Benjamin, P.R.Shapiro (University of Texas at Austin)

We have calculated the time-dependent, nonequilibrium thermal and ionization history of gas cooling radiatively from $10^{6} K$ in a one-dimensional, planar,steady-state flow model of the galactic fountain, including the effects of radiative transfer. We find that inclusion of the effects of self-ionization of the flow, combined with the requirement that the gas undergo a constant density (isochoric) phase in its evolution allows such a flow to match the observed galactic halo column densities of C IV, Si IV, and N V and UV emission from C IV and O III for a range of initial temperatures ($5.5 < log T_{0} <6.5$) and cooling regions sizes homogenous on scales of $D_{0}>15 pc$.For an initial flow velocity $v_{0} \sim100\,km/s$, comparable to the sound speed of a $10^{6} K$ gas, the initial density is found to be $n_{H,0} \sim\, 2\,\times\,10^{-2} \,cm^{-3}$, in reasonable agreement with other observational estimates of ionized halo gas, and $D_{0} \sim\,40\,pc$. We compare predicted $H \alpha$ fluxes, total ionizing flux, free-free radio emission, and broadband X-ray fluxes with observed values. Finally, we present results of $1-D$ hydrodynamical calculations of radiative shocks lead to the physical conditions necessary to produce such a cooling flow.

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