H3+: A new probe of the Galactic center

Takeshi Oka

Department of Astronomy and Astrophysicsand Department of Chemistry,

The Enrico Fermi Institute, The University of Chicago

ACS symposium “Molecules in Space”, Atlanta, March 30, 2006

Hot and diffuse clouds near the Galactic center probed by metastable H3

+

T. Oka, T. R. Geballe, M. Goto, T. Usuda, B. J. McCall, ApJ 632, 882 (2005)

Nature 384, 334 (1996)

4 1014 cm-2

6 1014 cm-2

H3+ toward the Galactic center

Geballe, McCall, Hinkle, Oka, ApJ 510, 251 (1999)

R(1, 1)u R(1, 0)

6

5

4

3

2

1

0

H3+

Col

umn

Den

sity

(10

14cm

-2)

50403020100

E(B-V) (mag)

AFGL2136

W33A

MonR2 IRS 3

AFGL961E

AFGL490

AFGL2591

8

6

4

2

0

H3+

Col

umn

Den

sity

(10

14cm

-2)

6543210

E(B-V) (mag)

OphP Cygni

HD 183143

WR 118

Cyg OB2 12

WR 104

Cyg OB2 5

WR 121

HD 168607

HD 194279

GC IRS 3

2 Ori

HD 20041

Dense clouds

McCall, Geballe, HinkleOka, ApJ 522,338(1999)

Diffuse clouds

McCall, Hinkle, Geballe, Moriarty-Schieven, Evans,Kawaguchi, Takano, Smith, Oka, ApJ 567, 391 (2002)

Per

N(H3+) ~ 3.6 ×1012 cm-2 AV

N(H3+) ~ 4.4 ×1013 cm-2 AV

The ubiquitous H3+

Dense

Diffuse

n

100

1

L

1

10

AV

10

1

N(H3+)

1

1

X(H3+)

1

10

ζ

1

10

X(H3+)diffuse ~ 10 X(H3

+)dense

10-9

10-8

10-7

10-6

10-5

10-4

10-3

10-2

10-1

100

101

102

103

104

105

106

n(X

)

10-1

100

101

102

103

104

105

106

n(H)

Dense Clouds Diffuse Clouds

H2

HCO

C+H3

+

V

1

1000

(H3+)total

1

100

H3+ is a powerful probe for diffuse cloudsN(H2)

S

1

100

Sightlines toward the Galactic center

Mezger, Duschl, Zylka (1996)Georgelin, Georgelin (1976)

AV = 25 ~ 40

Cotera, Simpson, Erickson, Colgan,Burton, Allen, ApJS 192, 123 (2000)

Toward Sgr A*

AV ~ 30 [AV]DISM ~ 20 , [AV]MC ~ 10

Whittet, Boogert, Gerakines, Schutte,Tielens, de Graauw, Prusti, van Dishoeck,Wesselius, Wright, ApJ 490, 729 (1997)

N(H3+)DISM: N(H3

+)MC ~ 20 : 1

The Central Molecular Zone (CMZ)R ~ 200 pcM ~ 5 ×107 M⊙

Dominantly molecularn(H2) > 104 cm-3

Volume filling factor 0.110 % of total ISMHot gasHigh velocity dispersionLow dust temperature

Mezger, Duschl, Zylka, A&A Rev. (1996)

Morris, Serabyn, ARA&A (1996)

Genzel, Hollenbach, Townes (1994)

CMZ

OH, H2CO, CO, CS, NH3, HCN H3+

Yusef-Zadeh, Morris, AJ (1987)

Nagata et al. (1990)Okuda et al. (1990)

Extraordinary radio emission

The Quituplet

LaRosa, Kassim, Lazio, Hyman, AJ 119, 207 (2000)

H3+ in the (3, 3) metastable level

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

The Subaru Telescope

32.9 K

361 K

J

KV = 2← 0

Sightline toward the Galactic center

The Central Molecular Zone

J

K

361 K

(J, K)

The ideal energy levels of H3+

(3, 3) metastable level

(1, 1) ground level

Δk = ± 3 forbidden transitions

27.2 days(2, 2) unstable level

(1, 0)

0 ±1 ±2 ±3 k

Ncrit ~ 200 cm-3

H3+ + H2 → (H5

+)* → H3+ + H2

Pan, Oka, ApJ 305, 518 (1986)

Oka, Shimizu2, Watson, ApJ (1971)

Oka, Epp, ApJ 613, 349 (2004)

(1, 1) ground levelCMZ and spiral arms

(3, 3) metastable level All CMZ

(2, 2) unstable level Neither

CO Mostly spiral arms

High temperature

Low density

Enter the Gemini South Observatory

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

Whiteoak, Gardner, MNRAS (1979)

Dimension of the -100 km/s cloud

ζL = 2 ke N(H3+) (nC/nH)SV RX / f

7.3 ×10-8 cm3/s 1.6 ×10-4 1

1.6 ×1015 cm-2 3 - 10

Sodroski et al ApJ 452, 262 (1995)

ζL = (1.1 – 3.7) ×105 cm/s

ζ (s-1) L (pc)

3×10-17 (1.2 – 4.0) k3×10-16 120 – 4003×10-15 12 – 40

Other stars in the quintuplet cluster

Oka, Geballe, Goto, Usuda, McCall, ApJ (2005)

Other stars within 30 pc

Nagata, Hyland, Straw, Sato, Kawara, ApJ 1993

AA comparison

Main Results so far

• Vast amount of diffuse 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 ~ 100 pc• Ionization rate ~ 10-15 s-1

Volume filling factor of dense clouds 0.01

The Galactic centerThe Central Molecular Zone (CMZ)

The treasure house of H3+

Discovery of metastable H3

+

Revelation of warm and diffuse gas

Cold30 K>104 cm-3

Hot104 K~102 cm-3

Ultrahot107-8 K~0.3 cm-3

Warm250 K~102 cm-3

CO, CS X-rayH3+ Radio scattering

Volume filling factor f

0.1 0.5 - 1 ~ 0.5 «10.01

Extragalactic H3+

Geballe, Goto, Usuda, Oka, McCall ApJ in press

Z = 0.05821

Controversies

T. Oka No hot gas in the Expanding Molecular Ring

F. Le Petit Diffuse gas cannot be that hot

J. Black Infrared pumping

(1, 0)

(3, 0)

(2, 0)

(3, 3)

F. Yusef-Zadeh 4 categories of gases ApJ 637, L101 (2006)

Linnott & Rawlings Dynamically evolving cloud A&A 448, 425 (2006)

Dahmen, Hüttemeister, Wilson, Mauersberger, A&A, 331, 959 (1998)

望遠鏡と分光器

UKIRT 3.8 m CGS4 8 km s-1 Mauna Kea

すばる　 8 m IRCS 15 km s-1 Mauna Kea

Gemini South 8 m Phoenix 5 km s-1 Cerro Pachon