CII in the Interstellar Medium: Excitation by H2 Revisited

Abstract

C${}^{+}$ is a critical constituent of many regions of the interstellar medium, as it can be a major reservoir of carbon and, under a wide range of conditions, the dominant gas coolant. Emission from its 158$\mu$m fine structure line is used to trace the structure of photon dominated regions in the Milky Way and is often employed as a measure of the star formation rate in external galaxies. Under most conditions, the emission from the single [CII] line is proportional to the collisional excitation rate coefficient. We here used improved calculations of the deexcitation rate of [CII] by collisions with H${}_2$ to calculate more accurate expressions for interstellar C${}^{+}$ fine structure emission, its critical density, and its cooling rate. The collision rates in the new quantum calculation are $\sim$ 25% larger than those previously available, and narrow the difference between rates for excitation by atomic and molecular hydrogen. This results in [CII] excitation being quasi-independent of the molecular fraction and thus dependent only on the total hydrogen particle density. A convenient expression for the cooling rate at temperatures between 20 K and 400 K, assuming an LTE H${}_2$ ortho to para ration is $\Lambda (\mathrm{LTE}\mathrm{OPR})=\left(11.5+4.0e^{-100\mathrm{K}/T^{\mathrm{kin}}}\right)e^{-91.25\mathrm{K}/T^{\mathrm{kin}}}n({\mathrm{C}}^{+})n({\mathrm{H}}_2)\times 10^{-24}\mathrm{ergs}{\mathrm{cm}}^{-3}{\mathrm{s}}^{-1}$. The present work should allow more accurate and convenient analysis of the [\CII] line emission and its cooling.

References in corpus (4)

• A Herschel [CII] Galactic plane survey I: the global distribution of ISM gas components
• Rotational quenching of H2CO by molecular hydrogen: cross-sections, rates, pressure broadening
• Direct Imaging of a Compact Molecular Outflow from a Very Low-luminosity Object; L1521F-IRS
• Rotational quenching rate coefficients for H_2 in collisions with H_2 from 2 to 10,000 K

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