Journal Article

Absorption-Line Survey of H[math] toward the Galactic Center Sources. III. Extent of Warm and Diffuse Clouds

Miwa Goto, Tomonori Usuda, Thomas R. Geballe, Nick Indriolo, Benjamin J. Mccall, Thomas Henning and Takeshi Oka

in Publications of the Astronomical Society of Japan

Volume 63, issue 2, pages L13-L17
Published in print April 2011 | ISSN: 0004-6264
Published online April 2011 | e-ISSN: 2053-051X | DOI:

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  • Galaxies
  • Interstellar Medium


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We present a follow-up observation on Geballe and Oka (2010, ApJ, 709, L70), who found high column densities of H[math] [math] 100 pc apart from the Galactic center on the lines of sight to 2MASS J17432173[math]2951430 (J1743) and 2MASS J17470898[math]2829561 (J1747). The wavelength coverages on these sightlines have been extended in order to observe two key transitions of H[math] — [math](3, 3)[math] and [math](2, 2)[math] — which constrain the temperature and density of the environment. The profiles of the H[math] [math](3, 3)[math] line, which is due only to gas in the Galactic center, closely match the differences between the H[math] [math](1, 1)[math] and CO line profiles, just as they do for previously studied sightlines in the Galactic center. Absorption in the [math](2, 2)[math] line of H[math] is present in J1747 at velocities of between [math]60 and [math]100 km s[math]. This is the second clear detection of this line in the interstellar medium after GC IRS 3 in the Central cluster. The temperature of the absorbing gas in this velocity range is 350 K, significantly warmer than that of diffuse clouds in other parts of the Central Molecular Zone. This indicates that the absorbing gas localizes on the Sgr B molecular cloud complex. The warm and diffuse gas revealed by Oka et al. (2005, ApJ, 632, 882) apparently extends to [math]100 pc, but there is a hint that its temperature is somewhat lower in the line of sight to J1743 than elsewhere in the Galactic center. The observation of H[math] toward J1747 is compared with the recent Herschel observation of H[math]O[math] toward Sgr B2, and their chemical relation and remarkably similar velocity profiles are discussed.

Keywords: Galaxy: center; ISM: clouds; ISM: lines and bands; ISM: molecules

Journal Article.  3312 words.  Illustrated.

Subjects: Galaxies ; Interstellar Medium

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