CH 3 GHz Observations of Molecular Clouds Along the Galactic Plane

Abstract

Spectra in the CH ${}^2{\Pi }_{1/2}$, J=1/2, F=1-1 transition at 3335 MHz were obtained in three 5-point crosses centered on the Galactic plane at $\ell =$ 50$\arcdeg$, 100$\arcdeg$, and 110$\arcdeg$. The lines of sight traverse both Giant Molecular Clouds (GMCs) and local, smaller entities. This transition is a good tracer of low-density molecular gas and the line profiles are very similar to CO(1-0) data at nearly the same resolution. In addition, the CH 3335 MHz line can be used to calibrate the CO-H${}_2$ conversion factor (X${}_{\mathrm{CO}}$) in low-density molecular gas. Although this technique underestimates X${}_{\mathrm{CO}}$ in GMCs, our results are within a factor of two of X${}_{\mathrm{CO}}$ values calibrated for GMCs by other techniques. The similarity of CH and CO line profiles, and that of X${}_{\mathrm{CO}}$ values derived from CH and more traditional techniques, implies that most of the molecular gas along the observed lines of sight is at relatively low densities ($n\le$ 10${}^3$ cm${}^{-3}$).

arXiv comment26 pages, 12 figures, submitted to the AJ, revised after referee report

References in corpus (5)

• The Milky Way in Molecular Clouds: A New Complete CO Survey
• The Physics of Star Formation
• A FUSE Survey of Interstellar Molecular Hydrogen in Translucent Clouds
• Infrared Excess and Molecular Clouds: A comparison of new suerveys of far-infrared and H I 21-cm emission at high galactic latitudes
• Comparative Chemistry of Diffuse Clouds IV: CH

Cited by in corpus (6)

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• Carbon Fractionation in PDRs
• Herschel observations of extra-ordinary sources: Detecting spiral arm clouds by CH absorption lines
• CH abundance gradient in TMC-1
• CH as a Molecular Gas Tracer and C-Shock Tracer Across a Molecular Cloud Boundary in Taurus
• CH 3 GHz Observations of the Galactic Center