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arXiv · 1811.07940

Do Spectroscopic Dense Gas Fractions Track Molecular Cloud Surface Densities?

Molly J. Gallagher·Adam K. Leroy·Frank Bigiel·Diane Cormier·María J. Jiménez-Donaire·Annie Hughes·Jérôme Pety·Eva Schinnerer·Jiayi Sun·Antonio Usero·Dyas Utomo·Alberto Bolatto·Mélanie Chevance·Christopher M. Faesi·Simon C. O. Glover·Amanda A. Kepley·J. M. Diederik Kruijssen·Mark R. Krumholz·Sharon E. Meidt·David S. Meier·Eric J. Murphy·Miguel Querejeta·Erik Rosolowsky·Toshiki Saito·Andreas Schruba
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Abstract

We use ALMA and IRAM 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 pc 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 pc 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.

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Molly J. Gallagher, Adam K. Leroy, Frank Bigiel, Diane Cormier, María J. Jiménez-Donaire, Annie Hughes, Jérôme Pety, Eva Schinnerer, Jiayi Sun, Antonio Usero, Dyas Utomo, Alberto Bolatto, Mélanie Chevance, Christopher M. Faesi, Simon C. O. Glover, Amanda A. Kepley, J. M. Diederik Kruijssen, Mark R. Krumholz, Sharon E. Meidt, David S. Meier, Eric J. Murphy, Miguel Querejeta, Erik Rosolowsky, Toshiki Saito, Andreas Schruba. 2018-11-19. Do Spectroscopic Dense Gas Fractions Track Molecular Cloud Surface Densities?. https://doi.org/10.3847/2041-8213%2Faaf16a

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