Galactic Center Region Concentrated stars and interstellar matter High Energy Density (gravity, MHD,...
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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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Harry Kroto Some spectroscopic issues in astrophysical chemistry
Oka Introductory remark
Jacek Krelowski Absorption spectra of dark interstellar clouds
John Maier Gas phase laboratory studies of electron spectra of carbon containing molecules of relevance to astrophysics
Wolfgand Krätschmer Carbon clusters as interstellar molecules and grains
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Astronomers’ Periodic Table
Ben McCall
HHe
C N O Ne
Si S ArMg
Fe
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Metastable H3+ near the Galactic center:
Interplay between radiative and collisional interactions
Thomas R. Geballe Gemini Observatory
Miwa Goto Max-Planck-Institut für Astronomie
Tomonori Usuda Subaru Telescope
Benjamin J. McCall University of Illinois, Urbana-Champaign
Interstellar Reactions, Dresden, June 6, 2005
Takeshi Oka
Department of Chemistry and Department of Astronomy and Astrophysics
The Enrico Fermi Institute, The University of Chicago
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1975 H–C≡C–C≡C–C≡N H–C≡C–C≡C–C≡C–C≡N H–C≡C–C≡C–C≡C–C≡C–C≡N
C60
H3+
H 2
H 2+
C H 3+
C H 5+
C H 4
C H2 3+
C H2 2
C H3+
C H3 3+
C Hm n
C H+
C H 2+
N H2
+
H C O+
O H+
H O2+
H O3
+H O2
O H
C H C N H2 5
+
C H C N H3
+
C H N H3 2
+
H C N2
+
H C N
C H N H3 2
C H N H2
C H C N3
C H C N2 5
C H
C H C O3
+
C H O H3 2
+
C H C O2
C H O H3
H C OC H O H
C H O C H
2
2 5
3 3
C H2 5
+C H2 4
H C O2 3
+C O3
C H2
H C N3 3
+H C N3
H C N5
H C N7
H C N9
H C N11
C H3
C 4
+
C H4+
C H4 2+
C H4 3+
C H4
C H3 2
cosm ic ray
H 2N 2
C OO
H 2
H 2
e
e
e
ee
e
e
N
N H 3
H C N
C H C N3
e
C O
H O2
C H O H , e3
C
H 2
H 2
H 2
e
e
C H 3
+e
e eH C N
C+
e
C+
H 2
e eC
+
H 2H 2
e
C O
C
H
+
e
e
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2005 Hot and Diffuse Clouds near GC Probed by Metastable H3+
Oka, Geballe, Goto, Usuda, McCall
1998 – 2002 Ubiquity, Dense and Diffuse Clouds McCall, Geballe, Hinkle, Oka
Historical Sketch of H3+ Observation
+
1951
1970
1996
1980 Oka, PRL. 45, 531Laboratory Spectrum
1996Geballe, Oka, Nature 384, 334
Interstellar H3+, Discovery
H
H2
H3+
1989 - 95
2002 Metastable H3+, Discovery
Goto, McCall, Geballe, Oka, et al.
1975
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Three Proton System
I = 3/2 ortho gI = 4
I = 1/2 para gI = 2
+
J
K32.9 K
361 K
(J, K)
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Symmetry Breaking : forbidden Δk = ± 3 transitions
Interstellar NH3 Oka, Shimizu, Shimizu, Watson, ApJ 165, L15 (1971)
Interstellar H3+ Pan, Oka, ApJ 305, 518 (1986)
μ
Critical Density 200 cm-3
K
Collision H3+ + H2 → (H5
+)* → H3+ + H2
J
(J, K)
K
27.2 days
(3,3) metastable
(2,2) unstable
(1,1) ground(1,0)
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The Central Molecular Zone
M ~ 5 ×107 M⊙
Dominantly molecularn(H2) > 104 cm-4
Volume filling factor 0.1Hot gas T ~ 300 KHigh velocity dispersionLow dust temperature
Mezger, Duschl, Zylka, A&A Rev. (1996)
Morris, Serabyn, ARA&A (1996)
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Telescopes and Spectrometers
UKIRT 3.8 m CGS4 8 km s-1 Mauna Kea
Subaru 8 m IRCS 15 km s-1 Mauna Kea
Gemini South 8 m Phoenix 5 km s-1 Cerro Pachon
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Galactic plane
Quintuplet
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Yusef-Zadeh, Morris, AJ, 94, 1178 (1987)
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The Quintuplet
Okuda et al. ApJ 351, 89 (1990)
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Discovery of metastable H3+
Goto, McCall, Geballe, Usuda,Kobayashi, Terada, OkaPASJ, 54, 951 (2002)
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(1,1) ground
(3,3) metastable
(2,2) unstable
CO
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The Expanding Molecular RingKaifu, Kato, Iguchi, Nature (1972)Scoville, ApJ (1972)
Whiteoak, Gardner, MNRAS (1979)
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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
-100 km/s 0 km/s
-50 km/s
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Radiation Collision Reaction
Rigorous Selection Rules Approximate Rules Random
+ - ΔJ = ± 1, 0
ortho para ΔI = 0 ortho para ΔI = 0 ΔItotal = 0
A
A
B
B
C
A
D
B
Ψ’
ψ
Trad 3 K « Tkin
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Rate Equations
1' ' ' '2
' '
( ) exp( )2
J K JK JK J KJK JK
J K
g E Ek C
g kT
2
' '' '
' '
' '' '
' '
( )( ) ( )
( ' ') ( )
( ' ') ( )
( ) ( ) ( ) ( )
J K JKJK J K
J K
J K JKJK J K
J K
e XX
dn JKn H f JK
dt
A n J K A n JK
k n J K k n JK
k n e n JK k n X n JK
Production
Spontaneous emission 4 10-7 s-
1
Collision n(H2) 100 cm-3 10-7 s-1
Destruction 10-9 s-1
10-17 s-1
10-7 cm3 s-1 10-9 cm3 s-1
' '' '
' ' ' '
exp( )J KJK JK JK J KJKJ K J K
k g E E
k g kT
H3+ + H2 (H5
+)* H3+ + H2
Detailed balance
Cosmic ray ionization
Dissociative recombination Proton hop reaction
0 =
Steady State
Oka, Epp ApJ, 613, 349 (2004)
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)2,2(
)3,3(
N
N
Discovery of high temperature (T ~ 250 K), low density (n ≤ 100 cm-3) clouds
)1,1(
)3,3(
N
N
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