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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 Institute for Astronomy 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 Institute for Astronomy Tomonori Usuda Subaru Telescope Benjamin J. McCall University of Illinois, Urbana-Champaign Takeshi Oka Department of Chemistry and Department of Astronomy and Astrophysics The Enrico Fermi Institute, The University of Chicago EFI lunch seminar May 3, 2005

  2. 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 Vacuum 1916 n(H3+) » n(H2+) Arthur Dempster 1925 H2+ + H2→ H + H3+ Thorfin Hogness H 1951 1961 Interstellar H3+ , predictionEarl McDaniel H2 1973 H3+ + X → H2 + HX+ Bill Klemperer 1975 1970 Laser Spectroscopy T.G. Array Detector H3+ B.M. 1996 + M.G. Ubiquity Dense and Diffuse Clouds Large Diameter Telescope 2005 Hot and Diffuse Clouds near GC Probed by Metastable H3+

  3. + Three Proton System ++ = uuu p = uud n = udd I = 3/2 ortho I = 1/2 para

  4. Breaking Symmetry ortho ortho para para J Metastable 8 hrs μ 16 hrs 20.4 days Critical Density 200 cm-3 27.2 days K Collision H3+ + H2→ (H5+)* → H3+ + H2 Interstellar NH3 Oka, Shimizu, Shimizu, Watson, ApJ 165, L15 (1971) Interstellar H3+ Pan, Oka, ApJ 305, 518 (1986)

  5. Galactic Center Region Center ~ 500 pc • Concentrated stars and interstellar matter • High Energy Density (gravity, MHD, kinetic) • Strong magnetic field : B ~ mG High external pressure: P/k@ 5 x 106 cm–3 K

  6. Extraordinary Radio Emission • Radio Arc • Arched Filaments • Nonthermal Filaments • Sgr A*

  7. The Central Molecular Zone M ~ 5 ×107 M⊙ Dominantly molecular n(H2) > 104 cm-4 Volume filling factor 0.01 Hot gas T ~ 300 K High Velocity Dispersion

  8. Quintuplet Galactic plane

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

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

  11. (1, 1) ground level CMZ and spiral arms (3, 3) metastable level All CMZ High temperature (2, 2) unstable level Neither Low density CO All spiral arms

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

  13. 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

  14. 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?

  15. Quintuplet Galactic plane

  16. Gemini South

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