SLIDE 1
Ay 102 Physics of the Interstellar Medium
supplemental material Hillenbrand – Winter Term 2019-2020
solar core
Studied via:
- HI (neutral H)
- metal lines
(neutral and lightly ionized)
this room
Ay 102 Physics of the Interstellar Medium supplemental material - - PowerPoint PPT Presentation
Ay 102 Physics of the Interstellar Medium supplemental material - - PowerPoint PPT Presentation
Ay 102 Physics of the Interstellar Medium supplemental material Hillenbrand Winter Term 2019-2020 solar core CNM and WNM this room Average T and n Atomic Gas Studied via: - HI (neutral H) - metal lines (neutral and lightly
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Probing CNM Gas:
OI and CII (and SI) have low lying energy levels that produce far-infrared emission lines.
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Probing CNM/WNM Gas:
Dopita & Sutherland
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Dopita & Sutherland
Can infer column density N from absorption due to metals.
Probing CNM/WNM Gas:
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Probing CNM/WNM Gas: HI
- https://www.youtube.com/watch?v=Q2mgpsTFuV8
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HI Map of our Galaxy from Within
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HI Map of our Galaxy from Within
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Most of the HI rotates around the Galactic Center, but there are also “high velocity clouds” that differ from the expected rotation curve by >50 km/s, and trace material that is infallingon to the Milky Way.
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Inferred Map
- f our Galaxy
from Above
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Within the Galactic Plane, we observe discrete clouds along any given line-of-sight, which trace spiral arms.
Data are atomic gas (HI) or molecular gas (H2) https://www.youtube.com/watch?v=HGwkZY4E64k
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vr vt
Systematic changes in radial velocity as a function of galactic longitude let us construct the galactic rotation curve.
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Rotation in Nearby Galaxy M 33
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Atomic Levels – “Hyperfine” Structure
drawn to scale (and thus hard to see!) now including electron spin coupling to nucleus spin
aligned spin
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Atomic Levels – not to scale now
beyond “fine” to “hyperfine” lines: electron spin coupling to nucleus “spin”.
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21 cm (radio)
- A. Glassgold
anti-aligned spin aligned spin
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- A. Glassgold
ê C10 é C01
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- A. Glassgold
ê C10 é C01
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- J. Williams
α α α
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- J. Williams
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- A. Glassgold
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- J. Williams
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Atomic Gas: The CNM and WNM
- HI is a major diagnostic though not the major coolant.
- Emission is ubiquitous; absorption is rare.
- In the Milky Way, typically n(HI) = 0.1 to a few cm-3
- Density variations and temperature variations found to be
anti-correlated, in a manner consistent with pressure equilibrium, so
- Two-phase model consisting of: cool, dense clouds that can