Astronomy and Astrophysics – Astronomy
Scientific paper
Nov 2001
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2001apj...561..238h&link_type=abstract
The Astrophysical Journal, Volume 561, Issue 1, pp. 238-243.
Astronomy and Astrophysics
Astronomy
5
Ism: Abundances, Ism: Clouds, Ism: Individual (Ivc 135+54-46, Draco Nebula), Radio Lines: Ism, Submillimeter
Scientific paper
Using the Heinrich-Hertz-Telescope we have detected for the first time the [C I] 3P1-->3P0 line transition at 492 GHz of neutral atomic carbon from two intermediate-velocity clouds (IVCs): IVC 135+54-46 and the Draco Nebula. Both clouds are located at high Galactic altitudes, more than 200 pc above the Galactic plane. The width of the [C I] line is quantitatively comparable to that of the 12CO rather than to that of the 13CO line, as commonly found for Galactic plane clouds. This indicates that neutral atomic carbon within the diffuse medium at high Galactic altitudes fills a significantly larger volume in comparison to the situation in dark or denser cirrus clouds close to the Galactic plane. Moreover, our observations suggest that for IVCs cooling by the [C I] line is as important as or even more important than that by the low level CO lines. PDR models used to approximate the observed line intensity ratios indicate that the molecular gas in high-altitude IVCs is exposed to a weak interstellar radiation field while its density must be high.
Fritz Thomas
Heithausen Andreas
Kerp Jürgen
Weiß Axel
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