Two Sightlines Toward the Galactic Center with Remarkable H_3^+ and CO Spectra

Details Two Sightlines Toward the Galactic Center with Remarkable H_3^+ and CO Spectra Two Sightlines Toward the Galactic Center with Remarkable H_3^+ and CO Spectra

Jun 2010

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2010mss..conferf06o&link_type=abstract

"International Symposium On Molecular Spectroscopy, 65th Meeting, Held 21-25 June, 2010 at Ohio State University. http://molspec

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Scientific paper

Until last year the known stars in the Galactic center with sufficiently smooth spectra and of sufficient brightness to be suitable for high resolution infrared absorption spectroscopy of H_3^+ and CO were limited to a narrow range of longitudes, from the central cluster of hot stars to approximately 30 pc east of the center. In that region we have discovered a vast amount of warm (T ˜ 250 K) and diffuse (n ˜ 100 cm-3) gas. In order to more fully characterize the gas within the r˜ 180 pc Central Molecular Zone (CMZ) it is necessary to find additional such stars that cover a much wider longitudinal range of sightlines. We are in the process of identifying luminous dust-embedded objects suitable for spectroscopy between 170 pc east and west and 14 pc north and south of Sgr A* using the Spitzer GLIMPSE and the 2MASS catalogues.
Here we present spectra of H_3^+ and CO towards two such objects, one located 140 pc west of Sgr A* close to Sgr E, and the other located on a line of sight to the Sgr B molecular cloud complex 85 pc to the east of Sgr A*. The sightline to the west passes through two dense clouds of unusually high negative velocities in Sgr E which show strong absorptions by both H_3^+ and CO. This sightline also samples a portion of the Expanding Molecular Ring (EMR) which shows strong H_3^+ absorption but undetectable CO clearly indicating that the gas is diffuse, similar to sightlines closer to Sgr A*. The H_3^+ spectrum toward Sgr B reveals at least ten absorption components covering over 200 km s-1 and by far the largest equivalent width ever observed in an interstellar H_3^+ line. The CO spectrum is similarly complex but covers a somewhat narrower velocity range indicating mixture of dense and diffuse environments is present along this line of sight. Together the CO and H_3^+ spectra appear to provide the first near-infrared view into that hotbed of star formation.
Although further characterization of gas in those two sightlines and many more new sightlines must await observations of H_3^+ and CO this July at the Gemini South Observatory, clearly we are opening up a new vista of the CMZ.
Oka, T, Geballe, T. R., Goto, M., Usuda, T., & McCall, B. J. 2005, ApJ, 632, 882
Goto, M, et al. 2008, ApJ, 668, 306
Geballe, T. R. & Oka, T. 2010, ApJL, 709, L70

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