H 3 + : A new probe of the Galactic center Takeshi Oka Department of Astronomy and Astrophysics and Department of Chemistry, The Enrico Fermi Institute, The University of Chicago ACS symposium “Molecules in Space”, Atlanta, March 30, 2006 Hot and diffuse clouds near the Galactic center probed by metastable H 3 + T. Oka, T. R. Geballe, M. Goto, T. Usuda, B. J. McCall, ApJ 632, 882 (2005)

Nature 384, 334 (1996) 4  cm -2 6  cm -2

H 3 + toward the Galactic center Geballe, McCall, Hinkle, Oka, ApJ 510, 251 (1999) R(1, 1) u R(1, 0)

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)  Per N(H 3 + ) ~ 3.6 ×10 12 cm -2 A V N(H 3 + ) ~ 4.4 ×10 13 cm -2 A V The ubiquitous H 3 +

Dense Diffuse n L 1 10 A V 10 1 N(H 3 + ) 1 X (H 3 + ) 1 10 ζ 1 10 X ( H 3 + ) diffuse ~ 10 X ( H 3 + ) dense V (H 3 + ) total H 3 + is a powerful probe for diffuse clouds N(H 2 ) S 1 100

Sightlines toward the Galactic center Mezger, Duschl, Zylka (1996) Georgelin, Georgelin (1976) A V = 25 ~ 40 Cotera, Simpson, Erickson, Colgan, Burton, Allen, ApJS 192, 123 (2000) Toward Sgr A * A V ~ 30 [A V ] DISM ~ 20, [A V ] MC ~ 10 Whittet, Boogert, Gerakines, Schutte, Tielens, de Graauw, Prusti, van Dishoeck, Wesselius, Wright, ApJ 490, 729 (1997) N(H 3 + ) DISM : N(H 3 + ) MC ~ 20 : 1

The Central Molecular Zone (CMZ) R ~ 200 pc M ~ 5 × 10 7 M ⊙ Dominantly molecular n(H 2 ) > 10 4 cm -3 Volume filling factor % of total ISM Hot gas High velocity dispersion Low dust temperature Mezger, Duschl, Zylka, A&A Rev. (1996) Morris, Serabyn, ARA&A (1996) Genzel, Hollenbach, Townes (1994) CMZ OH, H 2 CO, CO, CS, NH 3, HCN H3+H3+

Yusef-Zadeh, Morris, AJ (1987) Nagata et al. (1990) Okuda et al. (1990) Extraordinary radio emission The Quituplet LaRosa, Kassim, Lazio, Hyman, AJ 119, 207 (2000)

H 3 + in the (3, 3) metastable level Goto, McCall, Geballe, Usuda, Kobayashi, Terada, Oka PASJ, 54, 951 (2002) The Subaru Telescope 32.9 K 361 K J K V = 2← 0

Sightline toward the Galactic center The Central Molecular Zone

J K 361 K (J, K) The ideal energy levels of H 3 + (3, 3) metastable level (1, 1) ground level Δk = ± 3 forbidden transitions 27.2 days (2, 2) unstable level (1, 0) 0 ±1 ±2 ±3 k N crit ~ 200 cm -3 H H 2 → (H 5 + )* → H H 2 Pan, Oka, ApJ 305, 518 (1986) Oka, Shimizu 2, Watson, ApJ (1971) Oka, Epp, ApJ 613, 349 (2004)

(1, 1) ground level CMZ and spiral arms (3, 3) metastable level All CMZ (2, 2) unstable level Neither CO Mostly spiral arms High temperature Low density Enter the Gemini South Observatory

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

Dimension of the -100 km/s cloud 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 = (1.1 – 3.7) × 10 5 cm/s ζ (s -1 )L (pc) 3× (1.2 – 4.0) k 3 × – × – 40

Other stars in the quintuplet cluster

Oka, Geballe, Goto, Usuda, McCall, ApJ (2005) Other stars within 30 pc Nagata, Hyland, Straw, Sato, Kawara, ApJ 1993

A A comparison

Main Results so far Vast amount of diffuse gas High temperature: T ~ 250 K Low Density: n ~ 100 cm -3 H 3 + total column density: 4.3  cm -2 ¾ in CMZ, ¼ in intervening spiral arms ½ of H 3 + in CMZ in the Expanding Mol. Ring Pathlength ~ 100 pc Ionization rate ~ s -1 Volume filling factor of dense clouds 0.01

The Galactic center The Central Molecular Zone (CMZ) The treasure house of H 3 + Discovery of metastable H 3 + Revelation of warm and diffuse gas Cold 30 K >10 4 cm -3 Hot 10 4 K ~10 2 cm -3 Ultrahot K ~0.3 cm -3 Warm 250 K ~10 2 cm -3 CO, CSX-ray H3+H3+ Radio scattering Volume filling factor f ~ 0.5 «1 0.01

Extragalactic H 3 + Geballe, Goto, Usuda, Oka, McCall ApJ in press Z =

Controversies T. Oka No hot gas in the Expanding Molecular Ring F. Le PetitDiffuse gas cannot be that hot J. BlackInfrared pumping (1, 0) (3, 0) (2, 0) (3, 3) F. Yusef-Zadeh 4 categories of gases ApJ 637, L101 (2006) Linnott & Rawlings Dynamically evolving cloud A&A 448, 425 (2006)

Dahmen, Hüttemeister, Wilson, Mauersberger, A&A, 331, 959 (1998)

望遠鏡と分光器 UKIRT 3.8 m CGS4 8 km s -1 Mauna Kea すばる 8 m IRCS 15 km s -1 Mauna Kea Gemini South 8 m Phoenix 5 km s -1 Cerro Pachon