Dark Molecular Gas in Simulations of z ∼ 0 Disk Galaxies. Li, Q., Narayanan, D., Davè, R., & Krumholz, M. R. The Astrophysical Journal, 869:73, December, 2018. ![Dark Molecular Gas in Simulations of z ∼ 0 Disk Galaxies [link]](https://bibbase.org/img/filetypes/link.svg "link")
Paper doi abstract bibtex The H2 mass of molecular clouds has traditionally been traced by the CO(J = 1-0) rotational transition line. This said, CO is relatively easily photodissociated and can also be destroyed by cosmic rays, thus rendering some fraction of molecular gas to be “CO-dark.” We investigate the amount and physical properties of CO-dark gas in two z ∼ 0 disk galaxies and develop predictions for the expected intensities of promising alternative tracers ([C I] 609 μm and [C II] 158 μm emission). We do this by combining cosmological zoom simulations of disk galaxies with thermal-radiative-chemical equilibrium interstellar medium (ISM) calculations to model the predicted H I and H2 abundances and CO (J = 1-0), [C I] 609 μm, and [C II] 158 μm emission properties. Our model treats the ISM as a collection of radially stratified clouds whose properties are dictated by their volume and column densities, the gas-phase metallicity, and the interstellar radiation field (ISRF) and CR ionization rates. Our main results follow. Adopting an observationally motivated definition of CO-dark gas, i.e., H2 gas with W CO \textless 0.1 K km s-1, we find that a significant amount (≳50%) of the total H2 mass lies in CO-dark gas, most of which is diffuse gas, poorly shielded due to low dust column density. The CO-dark molecular gas tends to be dominated by [C II], though [C I] also serves as a bright tracer of the dark gas in many instances. At the same time, [C II] also tends to trace neutral atomic gas. As a result, when we quantify the conversion factors for the three carbon-based tracers of molecular gas, we find that [C I] suffers the least contamination from diffuse atomic gas and is relatively insensitive to secondary parameters.
@article{li_dark_2018,
title = {Dark {Molecular} {Gas} in {Simulations} of z ∼ 0 {Disk} {Galaxies}},
volume = {869},
issn = {0004-637X},
url = {http://adsabs.harvard.edu/abs/2018ApJ...869...73L},
doi = {10.3847/1538-4357/aaec77},
abstract = {The H2 mass of molecular clouds has traditionally been traced by the CO(J = 1-0) rotational transition line. This said, CO is
relatively easily photodissociated and can also be destroyed by cosmic rays, thus rendering some fraction of molecular gas to be
“CO-dark.” We investigate the amount and physical properties
of CO-dark gas in two z ∼ 0 disk galaxies and develop predictions for the expected intensities of promising alternative tracers ([C I] 609 μm and [C II] 158 μm emission). We do this by combining
cosmological zoom simulations of disk galaxies with
thermal-radiative-chemical equilibrium interstellar medium (ISM) calculations to model the predicted H I and H2 abundances and CO (J = 1-0), [C I] 609 μm, and [C II] 158 μm emission properties. Our model treats the ISM as a collection of radially stratified clouds whose properties are dictated by their volume and column densities, the gas-phase metallicity, and the interstellar radiation field (ISRF) and CR ionization rates. Our main results follow. Adopting an
observationally motivated definition of CO-dark gas, i.e., H2 gas with W CO {\textless} 0.1 K km s-1, we find that a significant amount (≳50\%) of the total H2 mass lies in CO-dark gas, most of which is diffuse gas, poorly shielded due to low dust column density. The CO-dark molecular gas tends to be dominated by [C II], though [C I] also serves as a bright tracer of the dark gas in many instances. At the same time, [C II] also tends to trace neutral atomic gas. As a result, when we quantify the conversion factors for the three carbon-based tracers of molecular gas, we find that [C I] suffers the least contamination from diffuse atomic gas and is relatively insensitive to secondary parameters.},
urldate = {2021-03-24},
journal = {The Astrophysical Journal},
author = {Li, Qi and Narayanan, Desika and Davè, Romeel and Krumholz, Mark R.},
month = dec,
year = {2018},
keywords = {ISM: molecules, astrochemistry, galaxies: ISM, methods: numerical},
pages = {73},
}
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We do this by combining cosmological zoom simulations of disk galaxies with thermal-radiative-chemical equilibrium interstellar medium (ISM) calculations to model the predicted H I and H2 abundances and CO (J = 1-0), [C I] 609 μm, and [C II] 158 μm emission properties. Our model treats the ISM as a collection of radially stratified clouds whose properties are dictated by their volume and column densities, the gas-phase metallicity, and the interstellar radiation field (ISRF) and CR ionization rates. Our main results follow. Adopting an observationally motivated definition of CO-dark gas, i.e., H2 gas with W CO \\textless 0.1 K km s-1, we find that a significant amount (≳50%) of the total H2 mass lies in CO-dark gas, most of which is diffuse gas, poorly shielded due to low dust column density. The CO-dark molecular gas tends to be dominated by [C II], though [C I] also serves as a bright tracer of the dark gas in many instances. At the same time, [C II] also tends to trace neutral atomic gas. As a result, when we quantify the conversion factors for the three carbon-based tracers of molecular gas, we find that [C I] suffers the least contamination from diffuse atomic gas and is relatively insensitive to secondary parameters.","urldate":"2021-03-24","journal":"The Astrophysical Journal","author":[{"propositions":[],"lastnames":["Li"],"firstnames":["Qi"],"suffixes":[]},{"propositions":[],"lastnames":["Narayanan"],"firstnames":["Desika"],"suffixes":[]},{"propositions":[],"lastnames":["Davè"],"firstnames":["Romeel"],"suffixes":[]},{"propositions":[],"lastnames":["Krumholz"],"firstnames":["Mark","R."],"suffixes":[]}],"month":"December","year":"2018","keywords":"ISM: molecules, astrochemistry, galaxies: ISM, methods: numerical","pages":"73","bibtex":"@article{li_dark_2018,\n\ttitle = {Dark {Molecular} {Gas} in {Simulations} of z ∼ 0 {Disk} {Galaxies}},\n\tvolume = {869},\n\tissn = {0004-637X},\n\turl = {http://adsabs.harvard.edu/abs/2018ApJ...869...73L},\n\tdoi = {10.3847/1538-4357/aaec77},\n\tabstract = {The H2 mass of molecular clouds has traditionally been traced by the CO(J = 1-0) rotational transition line. This said, CO is\nrelatively easily photodissociated and can also be destroyed by cosmic rays, thus rendering some fraction of molecular gas to be\n“CO-dark.” We investigate the amount and physical properties\nof CO-dark gas in two z ∼ 0 disk galaxies and develop predictions for the expected intensities of promising alternative tracers ([C I] 609 μm and [C II] 158 μm emission). We do this by combining\ncosmological zoom simulations of disk galaxies with\nthermal-radiative-chemical equilibrium interstellar medium (ISM) calculations to model the predicted H I and H2 abundances and CO (J = 1-0), [C I] 609 μm, and [C II] 158 μm emission properties. Our model treats the ISM as a collection of radially stratified clouds whose properties are dictated by their volume and column densities, the gas-phase metallicity, and the interstellar radiation field (ISRF) and CR ionization rates. Our main results follow. Adopting an\nobservationally motivated definition of CO-dark gas, i.e., H2 gas with W CO {\\textless} 0.1 K km s-1, we find that a significant amount (≳50\\%) of the total H2 mass lies in CO-dark gas, most of which is diffuse gas, poorly shielded due to low dust column density. The CO-dark molecular gas tends to be dominated by [C II], though [C I] also serves as a bright tracer of the dark gas in many instances. At the same time, [C II] also tends to trace neutral atomic gas. As a result, when we quantify the conversion factors for the three carbon-based tracers of molecular gas, we find that [C I] suffers the least contamination from diffuse atomic gas and is relatively insensitive to secondary parameters.},\n\turldate = {2021-03-24},\n\tjournal = {The Astrophysical Journal},\n\tauthor = {Li, Qi and Narayanan, Desika and Davè, Romeel and Krumholz, Mark R.},\n\tmonth = dec,\n\tyear = {2018},\n\tkeywords = {ISM: molecules, astrochemistry, galaxies: ISM, methods: numerical},\n\tpages = {73},\n}\n\n","author_short":["Li, Q.","Narayanan, D.","Davè, R.","Krumholz, M. 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