The Evolution of Gas Clouds Falling in the Magnetized Galactic Halo: High Velocity Clouds (HVCs) Originated in the Galactic Fountain

Abstract

In the Galactic fountain scenario, supernovae and/or stellar winds propel material into the Galactic halo. As the material cools, it condenses into clouds. By using FLASH three-dimensional magnetohydrodynamic simulations, we model and study the dynamical evolution of these gas clouds after they form and begin to fall toward the Galactic plane. In our simulations, we assume that the gas clouds form at a height of z=5 kpc above the Galactic midplane, then begin to fall from rest. We investigate how the cloud's evolution, dynamics, and interaction with the interstellar medium (ISM) are affected by the initial mass of the cloud. We find that clouds with sufficiently large initial densities (> 0.1 hydrogen atoms per cc) accelerate sufficiently and maintain sufficiently large column densities as to be observed and identified as high-velocity clouds (HVCs) even if the ISM is weakly magnetized (1.3 micro Gauss). We also investigate the effects of various possible magnetic field configurations. As expected, the ISM's resistance is greatest when the magnetic field is strong and perpendicular to the motion of the cloud. The trajectory of the cloud is guided by the magnetic field lines in cases where the magnetic field is oriented diagonal to the Galactic plane. The model cloud simulations show that the interactions between the cloud and the ISM can be understood via analogy to the shock tube problem which involves shock and rarefaction waves. We also discuss accelerated ambient gas, streamers of material ablated from the clouds, and the cloud's evolution from a sphere-shaped to a disk- or cigar-shaped object.

46 pages, 16 figures, 3 tables. Accepted for publication in ApJ

References in corpus (11)

• Cats and Dogs, Hair and A Hero: A Quintet of New Milky Way Companions
• The cold gaseous halo of NGC 891
• Accretion of gas onto nearby spiral galaxies
• Distances to Galactic high-velocity clouds. Complex C
• An Accurate Distance to High-Velocity Cloud Complex C
• The Generation and Dissipation of Interstellar Turbulence - Results from Large Scale High Resolution Simulations
• A Survey of O VI, C III, and H I in Highly Ionized High-Velocity Clouds
• Metallicity and Ionization in High Velocity Cloud Complex C
• The evolution of interstellar clouds in a streaming hot plasma including heat conduction
• Evaporation and condensation of spherical interstellar clouds. Self-consistent models with saturated heat conduction and cooling
• A Study of the Vertical Motion of Supernova Remnant Bubbles in the Interstellar Medium Drawn from the Results of Three-Dimensional MHD Simulations

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