1. H3+H3+

2. H 3 +, a new astrophysical probe: Revelation of warm and diffuse gas near the Galactic center Takeshi Oka Department of Astronomy and Astrophysics and Department of Chemistry, The Enrico Fermi Institute The University of Chicago Thomas R. Geballe Gemini Observatory Miwa Goto Max Planck Institute for Astronomy Tomonori Usuda Subaru Telescope Benjamin J. McCall University of Illinois, Urbana-Champaign Tetsuya Nagata Kyoto University Tomoharu Oka University of Tokyo Farhad Yusef-Zadeh Northwestern University Harvey Liszt National Radio Astronomy Observatory June 27, 2007 CSO

3. Thumbnail sketch of H 3 + + 1951 1970 1996 H H2H2 H3+H3+ Simplest polyatomic molecule CO Simple chemistryH 2 → H 2 + + e H 2 + + H 2 → H + H 3 + c.r. p Initiator of interstellar chemistry H 3 + + O → H 2 + OH + p Powerful informant of: Cosmic ray ionization rate ζ Temperature T density n Radial length of clouds L X(H 3 + ) diffuse ~ 10X(H 3 + ) dense ζL = 2 k e N(H 3 + ) (n C /n H )

4. 2005 Hot and Diffuse Clouds near GC Probed by Metastable H 3 + Oka, Geballe, Goto, Usuda, McCall, ApJ 632, 882 Progress of H 3 + observation 1980Oka, PRL. 45, 531Laboratory Spectrum 1996Geballe, Oka, Nature 384, 334Interstellar H 3 +, Discovery 1989 - 95 2002 Metastable H 3 +, Discovery Goto, McCall, Geballe, Usuda, Kobayashi, Terada, Oka PASJ, 54, 951 1998 – 2002 Ubiquity, Dense and Diffuse Clouds McCall, Geballe, Hinkle, Oka ζ diffuse ~ !0 ζ dense 1975

5. Inferred face-on view of the Central Molecular Zone Sawada, Hasegawa, Handa, Cohen, MNRAS 349, 1167 (2004) Oka, Hasegawa, Sato, Tsuboi, Miyazaki, ApJS 118, 455 (1998) 130 pc 100 km s -1 Quintuplet GCS3-2 130 pc 100 km s -1

6. Telescope and spectrometer UKIRT 3.8 m CGS4 8 km s -1 Mauna Kea 1982 Subaru 8.2 m IRCS 15 km s -1 Mauna Kea 2000 Gemini South 8 m Phoenix 5 km s -1 Cerro Pachon 2003 VLT 8.2 m CRIRES ≤3 km s -1 Cerro Paranal 2006

7. Breaking Symmetry Interstellar NH 3 Oka, Shimizu, Shimizu, Watson, ApJ 165, L15 (1971) Interstellar H 3 + 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 = 1/2 J K Collision H 3 + + H 2 → (H 5 + ) * → H 3 + + H 2 16 hrs 8 hrs The ideal rotational levels of H 3 + (3,3) (2,2) Unstable (1,1) Ground 361 K

8. Central Molecular Zone is the Treasure House of H 3 + R(1, 1) u R(1, 0) Geballe Phil. Trans. RSL A358, 2503 (2000) N(H 3 + ) = 3.8 × 10 14 cm -2 L = 21 pc N(H 3 + ) = 4.4 × 10 15 cm -2

9. 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 T = 250 K n ≤ 100 cm -3

10. Dimension of the discovered gas ζL = 2 k e N(H 3 + ) (n C /n H ) SV R X 7.3 ×10 -8 cm 3 /s1.6 ×10 -4 3.1 ×10 15 cm -2 3 - 10 Sodroski et al ApJ 452, 262 (1995) ζL = (2.5 – 8.4) × 10 5 cm/s ζ (s -1 ) L (pc) 10 -16 (0.8 - 2.1) k 10 -15 80 - 210 COBE DIRBE 130 pc 100 km s -1 Oka, Geballe, Goto, Usuda, McCall, ApJ 632, 882 (2005)

11. (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 GC T = 220 - 400 K n ≤ 100 cm -3 All show high T and low n

12. All stars: high N(H 3 + ) and hence high ζL N(H 3 + ) = (2.3 - 4.5) × 10 15 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 R X = 3 and ζ = 10 -15 s -1

13. Lazio & Cordes, ApJ 505, 715 (1998) 0.8 10 7 K 0.1 10 6 K 10 cm -3 0.1 10 2 K 10 4 cm -3 Enter a new category of gas in the CMZ Warm and diffuse gas250 K 10 2 cm -3 ? ? that is incompatible with two other gases

14. 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?

15. X-ray sources diffuse gas or point source? Mostly diffuseMostly discrete Koyama, Maeda, Sonobe, Takeshima, et al. 1996 Muno, Baganoff, Bautz, Brandt, et al. 2003 Wang, Gotthelf, Lang, 2002 Koyama, Makishima, Tanaka, Tsunemi, 1986 Revnivtsev, Sazonov, Gilfanov, et al. 2006 Warwick, Sakano, Decourchelle, 2006 Muno, Baganoff, Bautz, Brandt, et al. 2004 Koyama, Awaki, Kunieda, Takano, et al., 1989 Tanaka, 2002 Ebisawa, et al., 2005 Koyama et al. 2007 Suzaku Dec. 6, 2006

16. Lazio & Cordes, ApJ 505, 715 (1998) 0.8 10 7 K 0.1 10 6 K 10 cm -3 0.1 10 2 K 10 4 cm -3 Enter a new category of gas in the CMZ Warm and diffuse gas250 K 10 2 cm -3 0.01 ?

17. Summary Spectroscopy of H 3 + 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). CO Oka, Hasegawa, Hayashi, Handa, Sakamoto, ApJ 493, 730 (1998) Dahmen, Hüttemeister, Wilson, Mauersberger, A&A 331, 959 (1998) H 2 Rodriguez-Fernandez, Martin-Pintad, Fuente, et al. A&A 365, 174 (2001) CH Magnani, Zelenik, Dame, Engebreth, ApJ 636, 267 (2006) 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!