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arXiv · 1401.5072

An Alternative Accurate Tracer of Molecular Clouds: The "$X_{\rm CI}$-Factor"

Stella S. R. Offner·Thomas G. Bisbas·Tom A. Bell·Serena Viti
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Abstract

We explore the utility of CI as an alternative high-fidelity gas mass tracer for Galactic molecular clouds. We evaluate the X$_{\rm CI}$-factor for the 609 $μ$m carbon line, the analog of the CO X-factor, which is the ratio of the H$_2$ column density to the integrated $^{12}$CO(1-0) line intensity. We use 3D-PDR to post-process hydrodynamic simulations of turbulent, star-forming clouds. We compare the emission of CI and CO for model clouds irradiated by 1 and 10 times the average background and demonstrate that CI is a comparable or superior tracer of the molecular gas distribution for column densities up to $6 \times 10^{23}$ cm$^{-2}$. Our results hold for both reduced and full chemical networks. For our fiducial Galactic cloud we derive an average $X_{\rm CO}$ of $3.0\times 10^{20}$ cm$^{-2}$K$^{-1}$km$^{-1}$s and $X_{\rm CI}$ of $1.1\times 10^{21}$ cm$^{-2}$K$^{-1}$km$^{-1}$s.

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Stella S. R. Offner, Thomas G. Bisbas, Tom A. Bell, Serena Viti. 2014-01-20. An Alternative Accurate Tracer of Molecular Clouds: The "$X_{\rm CI}$-Factor". https://doi.org/10.1093/mnrasl%2Fslu013

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