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[37.01] Warm and Diffuse Gas near the Galactic Center probed by Metastable H3+

T.R. Geballe (Gemini Observatory), T. Oka (Univ. of Chicago), M. Goto (MPIA-Heidelberg), T. Usuda (Subaru Telescope), B.J. McCall (Univ. of Illinois)

Using observations of a line from the metastable (3,3) rotational level of H₃⁺ combined with measurements of other lines of H₃⁺ and CO, we have discovered a large quantity of high temperature (T~250K) and low density (n~100 cm^-3) gas within the central few hundred parsecs of the Galaxy. Some of this gas has velocities near -100 km s^-1 (LSR) and apparently is associated with the Expanding Molecular Ring at a distance of 180 pc from the nucleus; most of the remainder is at velocities near -50, 0, and + 50 km s^-1. Previous interpretations of the interstellar gas in the central few hundred parsecs have been that it is mostly in the form of dense clouds which have a filling factor of ~0.1. The observations reported here suggest that the filling factor of dense gas is much smaller than this. The metastable H₃⁺ level is not populated in a number of star-forming clouds far from the Galactic Center.

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Bulletin of the American Astronomical Society, 37 #2
© 2005. The American Astronomical Soceity.