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

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

Astronomers’ Periodic Table

Ben McCall

HHe

C N O Ne

Si S ArMg

Fe

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

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

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

Three Proton System

I = 3/2 ortho gI = 4

I = 1/2 para gI = 2

+

J

K32.9 K

361 K

(J, K)

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)

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)

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

Galactic plane

Quintuplet

Yusef-Zadeh, Morris, AJ, 94, 1178 (1987)

The Quintuplet

Okuda et al. ApJ 351, 89 (1990)

Discovery of metastable H3+

Goto, McCall, Geballe, Usuda,Kobayashi, Terada, OkaPASJ, 54, 951 (2002)

(1,1) ground

(3,3) metastable

(2,2) unstable

CO

The Expanding Molecular RingKaifu, Kato, Iguchi, Nature (1972)Scoville, ApJ (1972)

Whiteoak, Gardner, MNRAS (1979)

(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

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

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)

)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)

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

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?

Galactic plane

Quintuplet

Gemini South