Deformation induced martensitic transformation of metastable
Hot and Diffuse Gas near the Galactic Center Probed by Metastable H 3 +
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Transcript of Hot and Diffuse Gas near the Galactic Center Probed by Metastable H 3 +
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Hot and Diffuse Gas near the Galactic Center Probed by Metastable H3
+
Thomas R. Geballe Gemini Observatory Miwa Goto Max Planck Institute for Astronomy Tomonori Usuda Subaru Telescope Benjamin J. McCall University of Illinois, Urbana-Champaign
EFI lunch seminar May 3, 2005
Takeshi OkaDepartment of Chemistry and Department of Astronomy and
AstrophysicsThe Enrico Fermi Institute, The University of Chicago
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1911 Discovery J. J. Thomson
1916 n(H3+) » n(H2
+) Arthur Dempster1925 H2
+ + H2 → H + H3+ Thorfin Hogness
1961 Interstellar H3+ + , prediction, prediction Earl McDaniel
1973 H3+ + X → H2 + HX+ Bill Klemperer
1975
2005 Hot and Diffuse Clouds near GC Probed by Metastable H3+
Ubiquity Dense and Diffuse Clouds
Historical Sketch of H3+
T.G.
B.M.
M.G. +
1951
1970
1996
1980 Oka, PRL. 45, 531Laboratory Spectrum
1996Geballe, Oka, Nature 384, 334
Interstellar H3+, Discovery
Vacuum
Laser Spectroscopy
Array Detector
Large Diameter Telescope
H
H2
H3+
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Three Proton System
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I = 3/2 ortho
I = 1/2 para
++ = uuup = uudn = udd
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Breaking Symmetry
Interstellar NH3 Oka, Shimizu, Shimizu, Watson, ApJ 165, L15 (1971)
Interstellar H3+ Pan, Oka, ApJ 305, 518 (1986)
Metastable
27.2 days
20.4 days
μ
Critical Density
200 cm-3
ortho orthopara para
J
K
Collision H3+ + H2 → (H5
+)* → H3+ + H2
16 hrs8 hrs
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Galactic Center Region
• Concentrated stars and interstellar matter• High Energy Density (gravity, MHD, kinetic)• Strong magnetic field : B ~ mG
High external pressure: P/k 5 x 106 cm–3 K
Center ~ 500 pc
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Extraordinary Radio Emission
• Radio Arc– Arched Filaments– Nonthermal Filaments
• Sgr A*
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The Central Molecular Zone
M ~ 5 ×107 M⊙Dominantly molecularn(H2) > 104 cm-4
Volume filling factor 0.01Hot gas T ~ 300 KHigh Velocity Dispersion
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Galactic plane
Quintuplet
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The Quintuplet
Okuda et al. ApJ 351, 89 (1990)
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1. Sightline crosses spiral arms.2. Sightline passes though a more diffuse gas (AV=15-25 mag) than any other in the Galaxy. 3. Sightline passes through Galactic Center clouds - a unique and complex environment.
Inner 300 pc – showing Sgr B2 and Expanding Ring
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(1, 1) ground levelCMZ and spiral arms
(3, 3) metastable level All CMZ
(2, 2) unstable level Neither
CO All spiral arms
High temperature
Low density
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)2,2()3,3(
NN
Discovery of high temperature (T ~ 250 K), low density (n ≤ 100 cm-3) clouds
)1,1()3,3(
NN
Oka & Epp, ApJ 613,349 (2004)
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Main Results so far• Vast amount of gas• High temperature: T ~ 250 K• Low Density: n ~ 100 cm-3
• H3+ total column density: 4.3 1015 cm-2
• ¾ in CMZ, ¼ in intervening spiral arms• ½ of H3
+ in CMZ in the Expanding Mol. Ring• Pathlength ~ 50 pc• Ionization rate ~ 5 10-15 s-1
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Hot and Diffuse Gas, Questions abound
What is the heating mechanism?
How is the pressure balanced?
How are they related to molecular clouds and H II regions?
What is the relation to X-ray (-ray) sources?
What is their role in the strong magnetohydrodynamic effects?
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Galactic plane
Quintuplet
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Gemini South