EXPANDING DIFFUSE MOLECULAR GAS IN THE CENTRAL MOLECULAR ZONE

OF THE GALACTIC CENTER PROBED BY H3

+

69th International Symposium on Molecular Spectroscopy University of Illinois Urbana, Champaign,June 16, 2014

Takeshi Oka, University of Chicago, Chicago Tom Geballe, Gemini Observatory, Hilo Nick Indriolo, Johns Hopkins University, BaltimoreMiwa Goto, Universitäts-Sternwarte MünchenTomonori Usuda, National Astronomical Observatory of Japan

Harvey Liszt, National Radio Astronomy ObservatoryTomoharu Oka, Keio UniversityYoshiaki Sofue, Meisei UniversityFarhad Yusef-Zadeh, Northwestern University

The mysterious Galactic center

Radio continuum Reber, 194421 cm HI spectrum Rougoor & Oort 1960Molecular radio absorption Bolton et al. 1964Molecular radio emission Cheung et al. 1968Sub-mm continuum Hildebrand et al. 1978Far IR continuum Hoffmann & Frederick 1969IR atomic fine structure Aitken et al. 1974Infrared CO absorption Willner et al. 1979Infrared H2 emission Gatley et al. 1984X-rays Bowyer et al. 1965, Kellog et al. 1971γ-rays Clark et al. 1968

Radio CO emission Penzias, Jefferts & Wilson, 1971, ApJ, 165, 229

Infrared H2+ absorption Geballe & Oka, 1996, Nature, 384, 334

CO radio emission vs H3+ infrared absorption

CO emission H3+ absorption

Presence Dense gas (CO) Dense, diffuse gas (H2)Observation Everywhere Stars needed Front and back Front onlyResolution Beam size (~ pc) Stellar size (~ AU)Analysis Complicated SimpleN(X) ←Wν Saturated Linear

The Central Molecular Zone

CMZ

Scoville ApJ 175, L127 (1972)

Oka et al. ApJ (2005)

Oka et al. ApJS (1998)

Two opposing views on gas dynamicsGravity in the barred potential Gas moving inward.

“inevitable inflow toward the center of Galactic gravitationalPotential well” (Morris & Serabyn 1996)

Explosion Gas moving outward.Athanassoula MNRAS 1992

Sgr A*

CO

H3+(1,1)

H3+(3,3)

New stars

3 stars on the West end near Sgr. E α, α+, β

α L=3.8

α+L=7.0

βL=4.5

Sgr A*

The east most star (so far) λ˗

Star γ near Sgr. C

Star ι near Sgr. B

Star δ

Star θ

Symmetric (l – v) Diagram → Purely Expanding Ring

δθ

Kaifu, Kato, Iguchi, Nature, 238, 105 (1972)

OH

Scoville, ApJ, 175, L127 (1972)

H2CO

The Expanding Molecular Ring

Gas motion in barred potential

Real-space structureFace-on view

αV-l diagram

Rodríguez-Fernandez et al. 2006Sawada et al. 2004

Face-on view of the Central Molecular Zone

Conclusions(1) Absorption blue shifted Gas in the CMZ is expanding(2) The front of expansion forms a ring with a radius of ~ 140 pc and expanding velocity of ~ 140 km s-1

(3) Unlike the previously reported Expanding Molecular Ring, the ring is not rotating.(4) The face-on view of the CMZ is approximately circular and not an ellipse of a high eccentricity. (5) The results revive the idea of explosions of gas from the center within the last few million years.

(a) Expanding Molecular Ring Kaifu et al. (1972) 1055‒ 1056 erg Scoville (1972) 2 × 1055 erg (b) GC lobe 1055 erg Bland-Hawthorn,l Cohen (2003) (c) Fermi bubble

I am scared

Double RingGCR of Dense Gas + EMR of Diffuse Gas

years10140km/s

pc140 6

~100 pc 100 km/s

~140 pc 140 km/s

(1055 – 1056 erg) Kaifu et al.

(4 × 1054, 2 × 1055 erg) Scoville

(2 × 1054 erg) Sofue

100 pc Ring (GCR) of Dense (Dust) Clouds