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Hot and diffuse gas near the Galactic center probed by metastable H 3 +

Hot and diffuse gas near the Galactic center probed by metastable H 3 +. Thomas R. Geballe Gemini Observatory Miwa Goto Max-Planck-Institut f ü r Astronomie Tomonori Usuda Subaru Telescope

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Hot and diffuse gas near the Galactic center probed by metastable H 3 +

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  1. Hot and diffuse gas near the Galactic center probed by metastable H3+ Thomas R. Geballe Gemini Observatory Miwa Goto Max-Planck-Institut für Astronomie Tomonori Usuda Subaru Telescope Benjamin J. McCall University of Illinois, Urbana-Champaign Takeshi Oka Department of Astronomy and Astrophysics and Department of Chemistry The Enrico Fermi Institute, The University of Chicago Astro-ph/0507464 Subaru Telescope, August 3, 2005

  2. The Central Molecular Zone(CMZ) R ~ 200 pc M ~ 5 ×107 M⊙ Dominantly molecular n(H2) > 104 cm-3 Volume filling factor 0.1 10 % of total ISM Hot gas T ~ 300 K High velocity dispersion Low dust temperature H3+ OH, H2CO, CO, CS, NH3, HCN Morris, Serabyn, ARA&A (1996) Genzel, Hollenbach, Townes (1994) CMZ Mezger, Duschl, Zylka, A&A Rev. (1996)

  3. The central 30 pc of the CMZ The Quituplet Nagata et al. (1990) Okuda et al. (1990) Yusef-Zadeh, Morris, AJ (1987)

  4. Salient features of H3+ Protonated H2 (P.A.=4.4 eV), simplest polyatomic molecule Equilateral triangle, Infrared active 4μband Simple chemistry ζ Production H2→ H2+ + e H2+ + H2 → H3+ + H rate = ζn(H2) Destruction Dense cloud H3+ + CO → H2 + HCO+ Diffuse cloud H3+ + e → H + H + H n(H3+) constant N(H3+) → L cloud dimension n(H3+) ∽ ζN(H3+) → ζL ioniozation rate Ubiquity Dense cloud N(H3+) = 3.6 × 1012 cm-2 AV Diffuse cloud N(H3+) = 4.4 × 1013 cm-2 AV The most abundant molecular ion in the Universe 1961 1972 Initiator of interstellar chemistry H3++ O → OH+ + H2 OH+ → H2O+→ H3O+ → H2O

  5. Historical sketch of H3+ observation 1980 Laboratory Spectrum Oka, PRL. 45, 531 1989 - 95 Interstellar H3+, Discovery 1996 Geballe, Oka, Nature 384, 334 1975 H 1951 H2 1970 H3+ 1998 – 2002 Ubiquity, Dense and Diffuse Clouds McCall, Geballe, Hinkle, Oka 1996 + 2002 Metastable H3+, Discovery Goto, McCall, Geballe, Usuda, Kobayashi, Terada, Oka PASJ, 54, 951 • Hot and Diffuse Clouds near GC Probed by Metastable H3+ • Oka, Geballe, Goto, Usuda, McCall,Astro-ph/0507464

  6. H3+ more abundant in Diffuse Clouds Dense clouds McCall, Geballe, Hinkle Oka, ApJ 522,338(1999) N(H3+) ~ 3.6 ×1012 cm-2 AV N(H3+) ~ 4.4 ×1013 cm-2 AV Diffuse clouds McCall, Hinkle, Geballe, Moriarty-Schieven, Evans, Kawaguchi, Takano, Smith, Oka, ApJ 567, 391 (2002)  Per

  7. Sightlines toward the CMZ AV = 25 ~ 40 Cotera et al. (2000) Toward Sgr A* AV ~ 30 [AV]DISM ~ 20 , [AV]MC ~ 10 Whittet et al. (1997) LDISM: LMC ~ 200 : 1 N(H3+)DISM: N(H3+) ~ 20 : 1 Mezger, Duschl, Zylka (1996) Georgelin, Georgelin (1976)

  8. Discovery of H3+toward GC 2.5 × 1015 cm-2 GC IRS 3 GCS 3-2 2.8 × 1015 cm-2 Geballe, McCall, Hinkle, Oka, ApJ 510, 215 (1999)

  9. The ideal energy levels of H3+ ortho I = 3/2 + para I = 1/2 (J, K) H3+ + H2→ (H5+)* → H3+ + H2 J Δk = ± 3 forbidden transitions (3, 3) metastable level Ncrit ~ 200 cm-3 361 K (2, 2) unstable level 27.2 days (1, 0) (1, 1) ground level 32.9 K K Oka et al. ApJ, (1971) Oka & Epp, ApJ 613, 349 (2004) 0 ±1 ±2 ±3 k

  10. Discovery of metastableH3+ The Subaru Telescope Goto, McCall, Geballe, Usuda, Kobayashi, Terada, Oka PASJ, 54, 951 (2002)

  11. 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

  12. ground metastable T ~ 250 K EMR metastable unstable n ≤ 100 cm-3 unstable CO ground

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

  14. Dimension or the hot and diffuse clouds ζ L = 2keN(H3+)(nC/nH)SVRX/f = 3.7× 104 RX/f cm s-1 RX = (nC/nH)GC/(nC/nH)SV ~ 3 – 10, f ~ 1 COBE DIRBE Sodroski et al. ApJ 452, 262 (1995) Arimoto, Sofue, Tsujimoto, PASJ 48, 275 (1996) ζ L = (1 – 4) × 105 cm s-1 If L = 20 pc, ζ = (2 – 6) × 10-15 s-1 Extremely high ionization rate Liszt, A&A 398, 621 (2003)

  15. Nagata, Hyland, Straw, Sato, Kawara, ApJ 406, 501 (1993)

  16. Main Results so far • Vast amount of gas • High temperature: T ~ 250 K • Low Density: n ~ 100 cm-3 • H3+ total column density: 4.3  1015 cm-2 • ¾ in CMZ, ¼ in intervening spiral arms • ½ of H3+ in CMZ in the Expanding Mol. Ring • Pathlength ~ 50 pc • Ionization rate ~ 5 10-15 s-1 Volume filling factor of dense clouds « 0.1 [MISM]CMZ/[MISM] total « 0.1

  17. 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?

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

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

  20. Clouds vLSR range N(H3+) Temperature Density (km s-1) (1014 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 -100 km/s 0 km/s (3, 3) metastable level All CMZ -50 km/s High temperature (2, 2) unstable level Neither Low density

  21. Gemini South

  22. Historical Sketch of H3+ 1980 Laboratory Spectrum Oka, PRL. 45, 531 Interstellar H3+, Discovery 1996 Geballe, Oka, Nature 384, 334 1911 Discovery J. J. Thomson H 1951 1916 n(H3+) » n(H2+) Arthur Dempster 1925 H2+ + H2→ H + H3+ Thorfin Hogness H2 1961 Interstellar H3+ , predictionEarl McDaniel 1970 1973 H3+ + X → H2 + HX+ Herbst, Klemperer, Watson 1975 H3+ T.G. 1996 + B.M. Ubiquity Dense and Diffuse Clouds M.G. H3+ in the (3, 3) metastable level 2005 Hot and Diffuse Clouds near GC Probed by Metastable H3+

  23. Quintuplet Galactic plane

  24. (1, 1) ground level CMZ and spiral arms -100 km/s 0 km/s -50 km/s (3, 3) metastable level All CMZ High temperature (2, 2) unstable level Neither Low density CO All spiral arms

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