1. EXPANDING DIFFUSE MOLECULAR GAS IN THE CENTRAL MOLECULAR ZONE OF THE GALACTIC CENTER PROBED BY H 3 + 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, Baltimore Miwa Goto, Universitäts-Sternwarte München Tomonori Usuda, National Astronomical Observatory of Japan Harvey Liszt, National Radio Astronomy Observatory Tomoharu Oka, Keio University Yoshiaki Sofue, Meisei University Farhad Yusef-Zadeh, Northwestern University

2. The mysterious Galactic center Radio continuum Reber, 1944 21 cm HI spectrum Rougoor & Oort 1960 Molecular radio absorption Bolton et al. 1964 Molecular radio emission Cheung et al. 1968 Sub-mm continuum Hildebrand et al. 1978 Far IR continuum Hoffmann & Frederick 1969 IR atomic fine structure Aitken et al. 1974 Infrared CO absorption Willner et al. 1979 Infrared H 2 emission Gatley et al. 1984 X-rays Bowyer et al. 1965, Kellog et al. 1971 γ-rays Clark et al. 1968 Radio CO emission Penzias, Jefferts & Wilson, 1971, ApJ, 165, 229 Infrared H 2 + absorption Geballe & Oka, 1996, Nature, 384, 334

3. CO radio emission vs H 3 + infrared absorption CO emission H 3 + absorption Presence Dense gas (CO) Dense, diffuse gas (H 2 ) Observation Everywhere Stars needed Front and back Front only Resolution Beam size (~pc) Stellar size (~ AU) Analysis Complicated Simple N(X) ←W ν Saturated Linear The Central Molecular Zone CMZ Scoville ApJ 175, L127 (1972) Oka et al. ApJ (2005) Oka et al. ApJS (1998)

4. Two opposing views on gas dynamics Gravity in the barred potential Gas moving inward. “inevitable inflow toward the center of Galactic gravitational Potential well” (Morris & Serabyn 1996) Explosion Gas moving outward. Athanassoula MNRAS 1992 Sgr A* CO H 3 + (1,1) H 3 + (3,3)

5. New stars

6. 3 stars on the West end near Sgr. E α, α+, β α L=3.8 α+ L=7.0 β L=4.5 Sgr A*

7. The east most star (so far) λ ˗

8. Star γ near Sgr. C

9. Star ι near Sgr. B

10. Star δ

11. Star θ

12. Symmetric (l – v) Diagram → Purely Expanding Ring δ θ

13. Kaifu, Kato, Iguchi, Nature, 238, 105 (1972) OH Scoville, ApJ, 175, L127 (1972) H 2 CO The Expanding Molecular Ring

14. Gas motion in barred potential Real-space structure Face-on view α V-l diagram

15. Rodríguez-Fernandez et al. 2006 Sawada et al. 2004 Face-on view of the Central Molecular Zone

16. 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) 10 55 ‒ 10 56 erg Scoville (1972) 2 × 10 55 erg (b) GC lobe 10 55 erg Bland-Hawthorn,l Cohen (2003) (c) Fermi bubble

17. I am scared

18. Double Ring GCR of Dense Gas + EMR of Diffuse Gas ~100 pc 100 km/s ~140 pc 140 km/s (10 55 – 10 56 erg) Kaifu et al. (4 × 10 54, 2 × 10 55 erg) Scoville (2 × 10 54 erg) Sofue

19. 100 pc Ring (GCR) of Dense (Dust) Clouds