Spectroscopy of H3+ and CO

toward the Galactic center

Takeshi Oka, Christopher P. Morong, Department of AstronomyAnd Astrophysics and Department of Chemistry University of Chicago

Thomas R. Geballe, Gemini Observatory, Hilo, Hawaii

Miwa Goto, Max Planck Institute for Astronomy, Heidelberg, Germany

Tomonori Usuda, Kumiko S. Usuda, Subaru Telescope, Hilo Hawaii

Nicholas Indriolo, Benjamin J. McCall, Department of Chemistry andDepartment of Astronomy, University of Illinois at Urbana-Champaign

June 19, 2007 Columbus Meeting

Inferred face-on view of the Central Molecular ZoneThe Expanding Molecular Ring

Scoville, ApJ 175, L127 (1972)

145 km s-1

200 pc

EMR

Sawada, Hasegawa, Handa, Cohen, MNRAS 349, 1167 (2004)Oka, Hasegawa, Sato, Tsuboi, Miyazaki, ApJS 118, 455 (1998)

130 pc

100 km s-1

Telescope and spectrometer

UKIRT 3.8 m CGS4 40,000 Mauna Kea 1982 Subaru 　 8.2 m IRCS 20,000 Mauna Kea 2000Gemini South 8 m Phoenix 60,000 Cerro Pachon 2003VLT 8.2 m CRIRES 100,000 Cerro Paranal 2006

Breaking

Symmetry

Interstellar NH3 Oka, Shimizu, Shimizu, Watson, ApJ 165, L15 (1971)

Interstellar H3+ Pan, Oka, ApJ 305, 518 (1986)

Oka, Epp, ApJ 613, 349 (2004)

Metastable

27.2 days

20.4 days

μ

Critical Density 200 cm-3

Ortho I = 3/2

Para I = 1/2J

KCollision H3

+ + H2 → (H5+)* → H3

+ + H2

16 hrs8 hrs

The ideal rotational levels of H3+

(3,3)

(2,2)Unstable

(1,1)Ground

361 K

CO J = 1

(2,2) unstable

(3,3) metastable

(1,1) ground

Spectroscopy

Oka, Geballe, Goto, Usuda, McCall, ApJ 632, 882 (2005)

130 pc

100 km s-1

Dimension of the discovered gas

ζL = 2 ke N(H3+) (nC/nH)SV RX / f

7.3 ×10-8 cm3/s 1.6 ×10-4 1

3.1 ×1015 cm-2 3 - 10

Sodroski et al ApJ 452, 262 (1995)

ζL = (2.5 – 8.4) ×105 cm/s

ζ (s-1) L (pc)

10-16 (0.8 - 2.1) k 10-15 80 - 210

COBE DIRBE

120 pc

100 km s-1

Oka, Geballe, Goto, Usuda, McCall, ApJ 632, 882 (2005)

(2,2) densitometer

(3,3) thermometer

(1,1) ground level

(2,2) densitometer

(3,3) thermometer

(1,1) ground level

8 stars within 30 pc from GCall show high T and low n

T = 220 - 400 Kn ≤ 100 cm-3

All stars: high N(H3+) and hence high ζL

N(H3+) = (2.3 - 4.5) × 1015 cm-2

R(2, 2)l

R(1, 1)l

Q(1, 0)Q(1, 1)R(3, 3)l

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

R(2, 2)l

R(1, 1)l

Q(1, 0)Q(1, 1)R(3, 3)l

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

L ≥ 60 – 120 pc for RX = 3 and ζ = 10-15 s-1

Lazio & Cordes, ApJ 505, 715 (1998)

0.8 107 K

0.1 106 K 10 cm-3

0.1 102 K 104 cm-3

Enter a new category of gas in the CMZ

Warm and diffuse gas250 K 102 cm-3

0.01

??

that is incompatible with two other gases

Chandra 20 pc × 20 pc (0.5 – 8) keV Muno et al. ApJ 589, 225 (2003)

Warwick, Sakano Decourchelle (2006) Revnivtsev et al. (2006)

X-ray: Chandra comes to rescue

The hyper-strong radio scattering caused by folded magnetic field

rather than hot electrons?

Folded fields as the source of extreme radio-wave scattering in the Galactic center

Goldreich and Sridhar, ApJ 640, L159 (2006)

Summary

Spectroscopy of H3+ has revealed a new category of gas

in the Central Molecular Zone with high temperature (~ 250 K) and low density ( ≤ 100 cm-3) with a large volume filling factor (f ~ 1).

The finding drastically change the previous picture of the gas in the Central Molecular Zone.

We are in the process of observing a wider region of the Central Molecular Zone. We need bright YSO’s!

Harvey Liszt Phil. Trans. R. Soc. A 364, 3049 (2006)

ζ = 10-17s-1

ζ = 10-17s-1