We explore the utility of CI as an alternative high-fidelity gas mass tracer for Galactic molecular clouds. We evaluate the XCI-factor for the 609 μm carbon line, the analog of the CO X-factor, which is the ratio of the H2 column density to the integrated 12CO(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 6×1023 cm−2. Our results hold for both reduced and full chemical networks. For our fiducial Galactic cloud we derive an average XCO of 3.0×1020 cm−2K−1km−1s and XCI of 1.1×1021 cm−2K−1km−1s.
@article{arxiv.1401.5072,
title = {An Alternative Accurate Tracer of Molecular Clouds: The "$X_{\rm CI}$-Factor"},
author = {Stella S. R. Offner and Thomas G. Bisbas and Tom A. Bell and Serena Viti},
journal= {arXiv preprint arXiv:1401.5072},
year = {2014}
}
Comments
5 pages, 4 figures, 1 table, accepted to MNRAS Letters