The Fate of Intergalactic Gas Clouds

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The Fate of Intergalactic Gas Clouds

• Jeremy Harrison
• Chicago State University

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Introduction to High Velocity Gas Clouds (HVCs)

• How does drag affect HVCs?
• How long will it take our galaxy to eat high
  velocity clouds?

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AN ALL SKY MAP OF HIGH VELOCITY CLOUDS (Wakker et
al 2003)
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A few values and formulas
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(No Transcript)
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Numerical Analysis, Computer programs

Solve using Runge-Kutta Method. The
gravitational field, g, comes from the mass model
of the Galaxy. The drag coefficient,b, depends
on cloud column density and the ambient
density of the Galaxy. Runge-Kutta has various
test steps along the way to get a feel of how
the slope is going!
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No drag S. drag C. Drag 21 Density floor Rot. Scale 5 C. Drag 18 C. Drag 21 Rot. Scale
Equatorial cloud 1 x x x x x x x
Equatorial cloud 2 x x x x x x x
Equatorial cloud 3 x x x x x x x
Complex H x x x x x x x
Magellanic stream x x x x x x x
Polar Cloud x x x x x x x

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Equatorial Cloud 1 (No drag)
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Equatorial Cloud 2 (N1020 cm-2 Standard drag)
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Equatorial Cloud 1 (N1020 cm-2 Rotation drops
as e-z/(5 kpc)
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Polar Orbit Cloud 1 (N1020 cm-2 Standard drag)
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Complex H (N1018 cm-2 Standard drag)
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Dramatic (but Preliminary) Conclusions

• In the presence of drag, gas clouds tend to
  quickly move to circular orbits.
• For standard parameters, clouds moving in the
  equatorial plane reach a stable circular orbit in
  less than 750 Myrs. For clouds in polar orbits,
  it takes more than 2000 Myrs to circularize!
• Clouds typically end up at R10 to 20 kpc.
• For clouds with column density gt 1021 cm-2, the
  orbits are nearly ballistic. However, we do see
  some small decrease in velocity and a small
  change in z-component of angular momentum

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Special Thanks To

• My advisor , Dr. Robert A. Benjamin and
• NSF for funding the REU program.