Spectroscopy of H 3 + and CO toward the Galactic center Takeshi Oka, Christopher P. Morong, Department of Astronomy And 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 and Department of Astronomy, University of Illinois at Urbana-Champaign June 19, 2007 Columbus Meeting

Inferred face-on view of the Central Molecular Zone The Expanding Molecular Ring Scoville, ApJ 175, L127 (1972) 145 km s 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 2000 Gemini South 8 m Phoenix 60,000 Cerro Pachon 2003 VLT 8.2 m CRIRES 100,000 Cerro Paranal 2006

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 H 2 → (H 5 + ) * → H H 2 16 hrs 8 hrs The ideal rotational levels of H 3 + (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 k e N(H 3 + ) (n C /n H ) SV R X / f 7.3 ×10 -8 cm 3 /s1.6 × ×10 15 cm Sodroski et al ApJ 452, 262 (1995) ζL = (2.5 – 8.4) × 10 5 cm/s ζ (s -1 ) L (pc) ( ) k 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 GC all show high T and low n T = K n ≤ 100 cm -3

All stars: high N(H 3 + ) and hence high ζL N(H 3 + ) = ( ) × 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 = s -1

Lazio & Cordes, ApJ 505, 715 (1998) K K 10 cm K 10 4 cm -3 Enter a new category of gas in the CMZ Warm and diffuse gas250 K 10 2 cm ? ? 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 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). 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 = s -1