Simulations of High Velocity Clouds: High-Velocity High-Stage Ions

Details Simulations of High Velocity Clouds: High-Velocity High-Stage Ions Simulations of High Velocity Clouds: High-Velocity High-Stage Ions

May 2011

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2011aas...21812906k&link_type=abstract

American Astronomical Society, AAS Meeting #218, #129.06; Bulletin of the American Astronomical Society, Vol. 43, 2011

Astronomy and Astrophysics

Astronomy

Scientific paper

We present the results of hydrodynamic simulations of high velocity clouds (HVCs) carried out using FLASH. The simulations self-consistently trace the non-equilibrium ionization evolution of carbon, nitrogen, and oxygen in a realistic HVC geometry, in which a cool dense spherical cloud moves through hot, tenuous halo gas. In our simulations, H I is ablated from the clouds through shear instabilities and undergoes turbulent mixing with the hot ambient gas. High-stage ions (C IV, N V, and O VI) are abundant in these turbulent mixing layers. We investigate a suite of models with a range of model parameters (cloud size, cloud velocity, cloud density). The simulations run for 60-240 Myr, depending on the model parameters. We find that the cloud's initial velocity does not affect the rates of H I ablation or ionization or high-stage ion production over a wide range of velocities, from subsonic through transonic to supersonic. However, we find that the cloud's initial size does affect the rate at which cloud material is ablated and/or ionized: a smaller cloud loses its H I mass relative to its initial mass more rapidly than a larger cloud. We also find that large HVCs are able to survive as far as the Galactic disk in the form of neutral hydrogen and thus fuel star formation. Our models compare well with Complex C observations in terms of the observed high-stage ion column densities, the trend between N(O VI)/N(H I) and N(H I), the ion-to-H I ratios, and the ion-to-ion ratios.

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