Physical properties of CO-dark molecular gas traced by C+. Tang, N., Y., Li, D., Heiles, C., Wang, S., Pan, Z., C., & Wang, J., J. Astronomy & Astrophysics, 2016. ![Physical properties of CO-dark molecular gas traced by C+ [pdf]](https://bibbase.org/img/filetypes/pdf.svg "pdf")
Paper ![Physical properties of CO-dark molecular gas traced by C+ [link]](https://bibbase.org/img/filetypes/link.svg "link")
Website abstract bibtex Neither HI nor CO emission can reveal a significant quantity of so-called dark gas in the interstellar medium (ISM). It is considered that CO-dark molecular gas (DMG), the molecular gas with no or weak CO emission, dominates dark gas. We identified 36 DMG clouds with C$^+$ emission (data from Galactic Observations of Terahertz C+ (GOT C+) project) and HINSA features. Based on uncertainty analysis, optical depth of HI $\tau\rm_HI$ of 1 is a reasonable value for most clouds. With the assumption of $\tau\rm_HI=1$, these clouds were characterized by excitation temperatures in a range of 20 K to 92 K with a median value of 55 K and volume densities in the range of $6.2\times10^1$ cm$^-3$ to $1.2\times 10^3$ cm$^-3$ with a median value of $2.3\times 10^2$ cm$^-3$. The fraction of DMG column density in the cloud ($f\rm_DMG$) decreases with increasing excitation temperature following an empirical relation $f\rm_DMG=-2.1\times 10^-3T_(ex,\tau_HI=1)$+1.0. The relation between $f\rm_DMG$ and total hydrogen column density $N_H$ is given by $f\rm_DMG$=$1.0-3.7\times 10^20/N_H$. The values of $f\rm_DMG$ in the clouds of low extinction group ($A\rm_V \le 2.7$ mag) are consistent with the results of the time-dependent, chemical evolutionary model at the age of ~ 10 Myr. Our empirical relation cannot be explained by the chemical evolutionary model for clouds in the high extinction group ($A\rm_V > 2.7$ mag). Compared to clouds in the low extinction group ($A\rm_V \le 2.7$ mag), clouds in the high extinction group ($A\rm_V > 2.7$ mag) have comparable volume densities but excitation temperatures that are 1.5 times lower. Moreover, CO abundances in clouds of the high extinction group ($A\rm_V > 2.7$ mag) are $6.6\times 10^2$ times smaller than the canonical value in the Milky Way. #[Full version of abstract is shown in the text.]#
@article{
title = {Physical properties of CO-dark molecular gas traced by C+},
type = {article},
year = {2016},
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pages = {13},
websites = {http://arxiv.org/abs/1606.00949},
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abstract = {Neither HI nor CO emission can reveal a significant quantity of so-called dark gas in the interstellar medium (ISM). It is considered that CO-dark molecular gas (DMG), the molecular gas with no or weak CO emission, dominates dark gas. We identified 36 DMG clouds with C$^+$ emission (data from Galactic Observations of Terahertz C+ (GOT C+) project) and HINSA features. Based on uncertainty analysis, optical depth of HI $\tau\rm_HI$ of 1 is a reasonable value for most clouds. With the assumption of $\tau\rm_HI=1$, these clouds were characterized by excitation temperatures in a range of 20 K to 92 K with a median value of 55 K and volume densities in the range of $6.2\times10^1$ cm$^-3$ to $1.2\times 10^3$ cm$^-3$ with a median value of $2.3\times 10^2$ cm$^-3$. The fraction of DMG column density in the cloud ($f\rm_DMG$) decreases with increasing excitation temperature following an empirical relation $f\rm_DMG=-2.1\times 10^-3T_(ex,\tau_HI=1)$+1.0. The relation between $f\rm_DMG$ and total hydrogen column density $N_H$ is given by $f\rm_DMG$=$1.0-3.7\times 10^20/N_H$. The values of $f\rm_DMG$ in the clouds of low extinction group ($A\rm_V \le 2.7$ mag) are consistent with the results of the time-dependent, chemical evolutionary model at the age of ~ 10 Myr. Our empirical relation cannot be explained by the chemical evolutionary model for clouds in the high extinction group ($A\rm_V > 2.7$ mag). Compared to clouds in the low extinction group ($A\rm_V \le 2.7$ mag), clouds in the high extinction group ($A\rm_V > 2.7$ mag) have comparable volume densities but excitation temperatures that are 1.5 times lower. Moreover, CO abundances in clouds of the high extinction group ($A\rm_V > 2.7$ mag) are $6.6\times 10^2$ times smaller than the canonical value in the Milky Way. #[Full version of abstract is shown in the text.]#},
bibtype = {article},
author = {Tang, N. Y. and Li, D. and Heiles, C. and Wang, S. and Pan, Z. C. and Wang, J. J.},
journal = {Astronomy & Astrophysics},
number = {28055}
}
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It is considered that CO-dark molecular gas (DMG), the molecular gas with no or weak CO emission, dominates dark gas. We identified 36 DMG clouds with C$^+$ emission (data from Galactic Observations of Terahertz C+ (GOT C+) project) and HINSA features. Based on uncertainty analysis, optical depth of HI $\\tau\\rm_HI$ of 1 is a reasonable value for most clouds. With the assumption of $\\tau\\rm_HI=1$, these clouds were characterized by excitation temperatures in a range of 20 K to 92 K with a median value of 55 K and volume densities in the range of $6.2\\times10^1$ cm$^-3$ to $1.2\\times 10^3$ cm$^-3$ with a median value of $2.3\\times 10^2$ cm$^-3$. The fraction of DMG column density in the cloud ($f\\rm_DMG$) decreases with increasing excitation temperature following an empirical relation $f\\rm_DMG=-2.1\\times 10^-3T_(ex,\\tau_HI=1)$+1.0. The relation between $f\\rm_DMG$ and total hydrogen column density $N_H$ is given by $f\\rm_DMG$=$1.0-3.7\\times 10^20/N_H$. 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