1. Hot and Diffuse Gas near the Galactic Center Probed by Metastable H 3 + Thomas R. Geballe Gemini Observatory Miwa Goto Max-Planck-Institut für Astronomie Tomonori Usuda Subaru Telescope Benjamin J. McCall University of Illinois, Urbana-Champaign Max-Planck-Institute für Astronomie Juni 3, 2005 Takeshi Oka Department of Chemistry and Department of Astronomy and Astrophysics The Enrico Fermi Institute, The University of Chicago

2. The 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 10 6 cm –3 K Center ~ 500 pc

3. Extraordinary radio emission Radio Arc –Arched filaments –Nonthermal filaments Sgr A * Yusef-Zadeh, Morris, AJ (1987)

4. The Central Molecular Zone M ~ 5 × 10 7 M ⊙ Dominantly molecular n(H 2 ) > 10 4 cm -4 Volume filling factor 0.1 Hot gas T ~ 300 K High velocity dispersion Low dust temperature Mezger, Duschl, Zylka, A&A Rev. (1996) Morris, Serabyn, ARA&A (1996)

5. 1911 Discovery J. J. Thomson 1916 n(H 3 + ) » n(H 2 + ) Arthur Dempster 1925 H 2 + + H 2 → H + H 3 + Thorfin Hogness +, prediction 1961 Interstellar H 3 +, prediction Earl McDaniel 1973 H 3 + + X → H 2 + HX + Herbst, Klemperer, Watson 1975 2005 Hot and Diffuse Clouds near GC Probed by Metastable H 3 + Ubiquity Dense and Diffuse Clouds Historical Sketch of H 3 + T.G. B.M. M.G. + 1951 1970 1996 1980 Oka, PRL. 45, 531 Laboratory Spectrum1996 Geballe, Oka, Nature 384, 334 Interstellar H 3 +, Discovery H H2H2 H3+H3+ H 3 + in the (3, 3) metastable level

6. Ubiquitous H 3 + Production : Cosmic Ray 0.6 primary particles cm -2 s -1 H 2 → H 2 + + e - ζ (H 2 ) ζ ~ 3 × 10 -17 s -1 H 2 + + H 2 → H + H 3 + k L n(H 2 + )n(H 2 ) k L ~ 10 -9 cm 3 s -1 C.R. Destruction Dense Clouds (~10 4 cm -3 ) 40 % H 3 + + CO → H 2 + HCO + Rate = k L n(H 3 + )n(CO) k L ~ 10 -9 cm 3 s -1 Diffuse Clouds (~ 10 2 cm -3 ) 40 % H 3 + + e - → H + H + H Rate = k e n(H 3 + )n(e - ) k e ~ 10 -7 cm 3 s -1 n(H 3 + ) = [ζ/k L ][n(H 2 )/n(CO)] n(H 3 + ) = [ζ/k e ][n(H 2 )/n(e - )]

7. Special Chemistry of H 3 + Production  n(H 2 ) Destruction Dense cloud k L n(CO) n(H 3 + ) Diffuse cloud k e n(e - ) n(H 3 + ) n(H 3 + ) = = 10 -9 cm 3 s -1 10 -7 cm 3 s -1

8. 8 6 4 2 0 N (H 3 + ) in 10 14 cm -2 16012080400 A v 151050 A v 8 6 4 2 0 Dense Clouds Diffuse Clouds GC Dense clouds McCall, Geballe, Hinkle Oka, ApJ 522,338(1999) Diffuse clouds McCall, Hinkle, Geballe, Moriarty-Schieven, Evans, Kawaguchi, Takano, Smith, Oka, ApJ 567, 391 (2002) W33A AFGL2136 AFGL 2591 AFGL 490 AFGL 961E MonR2 IRS3 Cygnus OB2 #12 WR 118 # 5 WR 104 WR 121 HD 20041 183143 Ζ Per N(H 3 + ) 30~50 cm -2 !! Stevenson Object Ubiquitous H 3 +

9. Three Proton System + I = 3/2 ortho I = 1/2 para

10. Breaking Symmetry Interstellar NH 3 Oka, Shimizu, Shimizu, Watson, ApJ 165, L15 (1971) Interstellar H 3 + Pan, Oka, ApJ 305, 518 (1986) Metastable 27.2 days 20.4 days μ Critical Density 200 cm -3 ortho para J K Collision H 3 + + H 2 → (H 5 + ) * → H 3 + + H 2 16 hrs 8 hrs unstable

11. Discovery of metastable H 3 + Goto, McCall, Geballe, Usuda, Kobayashi, Terada, Oka PASJ, 54, 951 (2002)

12. 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 S 8 m Phoenix 5 km s -1 Cerro Pachon

13. Galactic plane Quintuplet

15. The Quintuplet Okuda et al. ApJ 351, 89 (1990)

18. ground unstable ground unstable metastable

19. The Expanding Molecular Ring Kaifu, Kato, Iguchi, Nature (1972) Scoville, ApJ (1972) Whiteoak, Gardner, MNRAS (1979)

20. 1.Sightline crosses spiral arms. 2.Sightline passes though a more diffuse gas (A V =15-25 mag) than any other in the Galaxy. 3.Sightline passes through Galactic Center clouds - a unique and complex environment. Inner 300 pc – showing Sgr B2 and Expanding Ring

21. (1, 1) ground level CMZ 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

22. Radiation Collision Reaction Rigorous Selection Rules Approximate Rules Random +  - ΔJ = ± 1, 0 ortho  para ΔI = 0 ortho  para ΔI = 0 ΔI total = 0 AAAA BBBB CACA DBDB Ψ’ψΨ’ψ T rad  3 K « T kin

23. Rate Equations Production Spontaneous emission 4  10 -7 s -1 Collision n(H 2 ) 100 cm -3 10 -7 s -1 Destruction 10 -9 s -1 10 -17 s -1 10 -7 cm 3 s -1 10 -9 cm 3 s -1 H 3 + + H 2  (H 5 + )*  H 3 + + H 2 Detailed balance Cosmic ray ionization Dissociative recombination Proton hop reaction 0 = Steady State Oka, Epp ApJ, 613, 349 (2004)

24. Discovery of high temperature (T ~ 250 K), low density (n ≤ 100 cm -3 ) clouds Oka & Epp, ApJ 613,349 (2004)

25. Clouds v LSR range N( H 3 + ) Temperature Density (km s -1 ) (10 14 cm -2 ) (K) (cm -3 ) -100 km s -1 -140 → -74 15.7 ± 1.7 270 ± 70 ≤ 50 -50 km s -1 -74 → -40 6.6 ± 1.3 250 ± 100 ≤100 0 km s -1 -40 → +32 8.4 ± 1.6 130 ± 100 ≤ 200 (1, 1) ground level CMZ and spiral arms (3, 3) metastable level All CMZ (2, 2) unstable level Neither High temperature Low density -100 km/s 0 km/s -50 km/s

27. Main Results so far Vast amount of gas High temperature: T ~ 250 K Low Density: n ~ 100 cm -3 H 3 + total column density: 4.3  10 15 cm -2 ¾ in CMZ, ¼ in intervening spiral arms ½ of H 3 + in CMZ in the Expanding Mol. Ring Pathlength ~ 50 pc Ionization rate ~ 5  10 -15 s -1

28. 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?

29. Interstellar Space Dense (molecular) clouds Diffuse clouds New class of clouds? Galactic Center Expanding molecular ring Galactic nucleus New class of clouds? Extragalactic Object Obscured AGN Magellanic clouds Circumstellar Space Planetary nebulae protoplanetary nebulae Planet Planets Proto-planet Exo-planet Treasure Hunting

31. Galactic plane Quintuplet

32. Gemini South