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Kwak, Kyujin
Computational Astrophysics Lab
Research Interests
  • Computational Fluid Dynamics
  • Astrophysical and Laboratory Plasma
  • Hydrodynamics with Radiation
  • Nuclear, Atomic, and Molecular Reactions

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THE EVOLUTION OF GAS CLOUDS FALLING IN THE MAGNETIZED GALACTIC HALO: HIGH-VELOCITY CLOUDS (HVCs) ORIGINATED IN THE GALACTIC FOUNTAIN

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Title
THE EVOLUTION OF GAS CLOUDS FALLING IN THE MAGNETIZED GALACTIC HALO: HIGH-VELOCITY CLOUDS (HVCs) ORIGINATED IN THE GALACTIC FOUNTAIN
Author
Kwak, KyujinShelton, Robin L.Raley, Elizabeth A.
Keywords
Galaxy: halo; ISM: clouds; ISM: magnetic fields; Methods: numerical; MHD
Issue Date
2009-07
Publisher
IOP PUBLISHING LTD
Citation
ASTROPHYSICAL JOURNAL, v.699, no.2, pp.1775 - 1788
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 (n >= 0.1 H atoms cm(-3)) 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 mu G). However, the ISM can provide noticeable resistance to the motion of a low-density cloud (n <= 0.01 H atoms cm(-3)) thus making it more probable that a low-density cloud will attain the speed of an intermediate-velocity cloud rather than the speed of an HVC. 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.
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DOI
10.1088/0004-637X/699/2/1775
ISSN
0004-637X
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PHY_Journal Papers
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