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Do spectroscopic dense gas fractions track molecular cloud surface densities?

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Abstract
We use Atacama Large Millimeter/submillimeter Array and Institute for Radio Astronomy in the Millimeter 30 m telescope data to investigate the relationship between the spectroscopically traced dense gas fraction and the cloud-scale (120 pc) molecular gas surface density in five nearby, star-forming galaxies. We estimate the dense gas mass fraction at 650 and 2800 pc scales using the ratio of HCN (1-0) to CO (1-0) emission. We then use high-resolution (120 pc) CO (2-1) maps to calculate the mass-weighted average molecular gas surface density within 650 or 2770 pc beam where the dense gas fraction is estimated. On average, the dense gas fraction correlates with the mass-weighted average molecular gas surface density. Thus, parts of a galaxy with higher mean cloud-scale gas surface density also appear to have a larger fraction of dense gas. The normalization and slope of the correlation do vary from galaxy to galaxy and with the size of the regions studied. This correlation is consistent with a scenario where the large-scale environment sets the gas volume density distribution, and this distribution manifests in both the cloud-scale surface density and the dense gas mass fraction.
Keywords
STAR-FORMATION, galaxies: ISM, galaxies: star formation, ISM: clouds, ISM: molecules, ISM: structure

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MLA
Gallagher, Molly J., et al. “Do Spectroscopic Dense Gas Fractions Track Molecular Cloud Surface Densities?” ASTROPHYSICAL JOURNAL LETTERS, vol. 868, no. 2, 2018.
APA
Gallagher, M. J., Leroy, A. K., Bigiel, F., Cormier, D., Jimenez-Donaire, M. J., Hughes, A., … Schruba, A. (2018). Do spectroscopic dense gas fractions track molecular cloud surface densities? ASTROPHYSICAL JOURNAL LETTERS, 868(2).
Chicago author-date
Gallagher, Molly J, Adam K Leroy, Frank Bigiel, Diane Cormier, Maria J Jimenez-Donaire, Annie Hughes, Jerome Pety, et al. 2018. “Do Spectroscopic Dense Gas Fractions Track Molecular Cloud Surface Densities?” ASTROPHYSICAL JOURNAL LETTERS 868 (2).
Chicago author-date (all authors)
Gallagher, Molly J, Adam K Leroy, Frank Bigiel, Diane Cormier, Maria J Jimenez-Donaire, Annie Hughes, Jerome Pety, Eva Schinnerer, Jiayi Sun, Antonio Usero, Dyas Utomo, Alberto Bolatto, Melanie Chevance, Chris Faesi, Simon CO Glover, Amanda A Kepley, JM Diederik Kruijssen, Mark R Krumholz, Sharon Meidt van der Wel, David S Meier, Eric Murphy, Miguel Querejeta, Erik Rosolowsky, Toshiki Saito, and Andreas Schruba. 2018. “Do Spectroscopic Dense Gas Fractions Track Molecular Cloud Surface Densities?” ASTROPHYSICAL JOURNAL LETTERS 868 (2).
Vancouver
1.
Gallagher MJ, Leroy AK, Bigiel F, Cormier D, Jimenez-Donaire MJ, Hughes A, et al. Do spectroscopic dense gas fractions track molecular cloud surface densities? ASTROPHYSICAL JOURNAL LETTERS. 2018;868(2).
IEEE
[1]
M. J. Gallagher et al., “Do spectroscopic dense gas fractions track molecular cloud surface densities?,” ASTROPHYSICAL JOURNAL LETTERS, vol. 868, no. 2, 2018.
@article{8622201,
  abstract     = {We use Atacama Large Millimeter/submillimeter Array and Institute for Radio Astronomy in the Millimeter 30 m telescope data to investigate the relationship between the spectroscopically traced dense gas fraction and the cloud-scale (120 pc) molecular gas surface density in five nearby, star-forming galaxies. We estimate the dense gas mass fraction at 650 and 2800 pc scales using the ratio of HCN (1-0) to CO (1-0) emission. We then use high-resolution (120 pc) CO (2-1) maps to calculate the mass-weighted average molecular gas surface density within 650 or 2770 pc beam where the dense gas fraction is estimated. On average, the dense gas fraction correlates with the mass-weighted average molecular gas surface density. Thus, parts of a galaxy with higher mean cloud-scale gas surface density also appear to have a larger fraction of dense gas. The normalization and slope of the correlation do vary from galaxy to galaxy and with the size of the regions studied. This correlation is consistent with a scenario where the large-scale environment sets the gas volume density distribution, and this distribution manifests in both the cloud-scale surface density and the dense gas mass fraction.},
  articleno    = {L38},
  author       = {Gallagher, Molly J and Leroy, Adam K and Bigiel, Frank and Cormier, Diane and Jimenez-Donaire, Maria J and Hughes, Annie and Pety, Jerome and Schinnerer, Eva and Sun, Jiayi and Usero, Antonio and Utomo, Dyas and Bolatto, Alberto and Chevance, Melanie and Faesi, Chris and Glover, Simon CO and Kepley, Amanda A and Kruijssen, JM Diederik and Krumholz, Mark R and van der Wel, Sharon Meidt and Meier, David S and Murphy, Eric and Querejeta, Miguel and Rosolowsky, Erik and Saito, Toshiki and Schruba, Andreas},
  issn         = {2041-8205},
  journal      = {ASTROPHYSICAL JOURNAL LETTERS},
  keywords     = {STAR-FORMATION,galaxies: ISM,galaxies: star formation,ISM: clouds,ISM: molecules,ISM: structure},
  language     = {eng},
  number       = {2},
  pages        = {9},
  title        = {Do spectroscopic dense gas fractions track molecular cloud surface densities?},
  url          = {http://dx.doi.org/10.3847/2041-8213/aaf16a},
  volume       = {868},
  year         = {2018},
}

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