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arXiv · 1007.3048

C$^+$ detection of warm dark gas in diffuse clouds

W. D. Langer·T. Velusamy·J. L. Pineda·P. F. Goldsmith·D. Li·H. W. Yorke
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Abstract

We present the first results of the Herschel open time key program, Galactic Observations of Terahertz C$^+$ (GOT C+) survey of the [CII] fine-structure line at 1.9 THz (158 microns) using the HIFI instrument on Herschel. We detected 146 interstellar clouds along sixteen lines-of-sight towards the inner Galaxy. We also acquired HI and CO isotopologue data along each line-of-sight for analysis of the physical conditions in these clouds. Here we analyze 29 diffuse clouds (A$_{V}$ < 1.3 mag.) in this sample characterized by having [CII] and HI emission, but no detectable CO. We find that [CII] emission is generally stronger than expected for diffuse atomic clouds, and in a number of sources is much stronger than anticipated based on their HI column density. We show that excess [CII] emission in these clouds is best explained by the presence of a significant diffuse warm H$_2$, dark gas, component. This first [CII] 158 micron detection of warm dark gas demonstrates the value of this tracer for mapping this gas throughout the Milky Way and in galaxies.

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W. D. Langer, T. Velusamy, J. L. Pineda, P. F. Goldsmith, D. Li, H. W. Yorke. 2010-07-19. C$^+$ detection of warm dark gas in diffuse clouds. https://doi.org/10.1051/0004-6361/201015088

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