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; Chris Faesi; Simon C.O. Glover; Amanda A. Kepley; J. M.Diederik Kruijssen; Mark R. Krumholz; Sharon E. Meidt; David S. Meier; Eric Murphy; Miguel Querejeta; Erik Rosolowsky; Toshiki Saito; Andreas Schruba

doi:10.3847/2041-8213/aaf16a

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
, Chris Faesi
, Simon C.O. Glover
, Amanda A. Kepley
, J. M.Diederik Kruijssen
, Mark R. Krumholz
, Sharon E. Meidt
, David S. Meier

Eric Murphy, Miguel Querejeta, Erik Rosolowsky, Toshiki Saito, Andreas Schruba

Physics And Astronomy

Research output: Contribution to journal › Article › peer-review

37 Scopus citations

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.

Original language	English
Article number	L38
Journal	Astrophysical Journal Letters
Volume	868
Issue number	2
DOIs	https://doi.org/10.3847/2041-8213/aaf16a
State	Published - Dec 1 2018

Bibliographical note

Publisher Copyright:
© 2018. The American Astronomical Society. All rights reserved..

Funding

We thank the anonymous referee for a fast and constructive report that improved the quality of this Letter. This Letter makes use of the following ALMA data: ADS/JAO.ALMA #2015.1.00956.S, ADS/JAO.ALMA #2013.1.00634.S, ADS/ JAO.ALMA #2011.0.00004.SV. ALMA is a partnership of ESO (representing its member states), NSF (USA) and NINS (Japan), together with NRC (Canada) and NSC and ASIAA (Taiwan), and KASI (Republic of Korea), in cooperation with the Republic of Chile. The National Radio Astronomy Observatory is a facility of the National Science Foundation operated under cooperative agreement by Associated Universities, Inc. The Joint ALMA Observatory is operated by ESO, AUI/NRAO and NAOJ. M.G. acknowledges generous support from the NRAO student observing support program. The work of M.G., A.K.L., J.S., and D.U. is partially supported by the National Science Foundation under grants No. 1615105, 1615109, and 1653300. F.B. acknowledges funding from the European Unions Horizon 2020 research and innovation programme (grant agreement No. 726384). E.S. acknowledges funding from the European Research Council (ERC) under the European Unions Horizon 2020 research and innovation programme (grant agreement No. 694343). A.U. acknowledges support from Spanish MINECO grants ESP2015-68964 and AYA2016-79006. S.C.O.G. acknowledges support from the DFG via SFB 881 “The Milky Way System” (sub-projects B1, B2 and B8). M.R.K. acknowledges support from the Australian Research Council (Discovery Projects award DP160100695, and the Centre of Excellence for All Sky Astrophysics in 3 Dimensions, project CE170100013). J.M.D.K. and M.C. gratefully acknowledge funding from the German Research Foundation (DFG) in the form of an Emmy Noether Research Group (grant No. KR4801/ 1-1). J.M.D.K. gratefully acknowledges funding from the European Research Council (ERC) under the European Unions Horizon 2020 research and innovation programme via the ERC Starting Grant MUSTANG (grant agreement No. 714907). D.C. is supported by the European Union’s Horizon 2020 research and innovation programme under the Marie Skłodowska-Curie grant agreement No. 702622. J.P. acknowledges support from the Program National “Physique et Chimie du Milieu Interstellaire” (PCMI) of CNRS/INSU with INC/INP, co-funded by CEA and CNES. E.R. acknowledges the support of the Natural Sciences and Engineering Research Council of Canada (NSERC), funding reference number RGPIN-2017-03987. 23 This work is partially based on observations carried out with the IRAM 30 m telescope. IRAM is supported by INSU/CNRS (France), MPG (Germany) and IGN (Spain). 24 http://phangs.org

Funders	Funder number
Centre National d’Etudes Spatiales
INSU
Instituto Nacional del Cáncer
CNRS Programme National Physique Chimie du Milieu Interstellaire
CNRS Centre National de la Recherche Scientifique
Marie Skłodowska-Curie fellow
California Earthquake Authority
Instituto Nacional de Pediatria
H2020 European Research Council
Horizon 2020
Horizon 2020 Framework Programme	694343, 726384, 714907, 702622
Ministerio de Economía y Competitividad	ESP2015-68964, AYA2016-79006
Australian Research Council	DP160100695
Natural Sciences and Engineering Research Council of Canada	RGPIN-2017-03987
Deutsche Forschungsgemeinschaft	KR4801/ 1-1
National Science Foundation Arctic Social Science Program	1615109, 1653300, 1615105
Centre of Excellence EcolChange	CE170100013

Keywords

galaxies: ISM
galaxies: star formation
ISM: clouds
ISM: molecules
ISM: structure

ASJC Scopus subject areas

Astronomy and Astrophysics
Space and Planetary Science

Access to Document

10.3847/2041-8213/aaf16a

Cite this

Gallagher, M. J., Leroy, A. K., Bigiel, F., Cormier, D., Jiménez-Donaire, M. J., Hughes, A., Pety, J., Schinnerer, E., Sun, J., Usero, A., Utomo, D., Bolatto, A., Chevance, M., Faesi, C., Glover, S. C. O., Kepley, A. A., Kruijssen, J. M. D., Krumholz, M. R., Meidt, S. E., ... Schruba, A. (2018). Do Spectroscopic Dense Gas Fractions Track Molecular Cloud Surface Densities? Astrophysical Journal Letters, 868(2), Article L38. https://doi.org/10.3847/2041-8213/aaf16a

@article{36cc591dbed34532b7203afe786ac3b1,

title = "Do Spectroscopic Dense Gas Fractions Track Molecular Cloud Surface Densities?",

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 = "galaxies: ISM, galaxies: star formation, ISM: clouds, ISM: molecules, ISM: structure",

author = "Gallagher, \{Molly J.\} and Leroy, \{Adam K.\} and Frank Bigiel and Diane Cormier and Jim{\'e}nez-Donaire, \{Mar{\'i}a J.\} and Annie Hughes and J{\'e}r{\^o}me Pety and Eva Schinnerer and Jiayi Sun and Antonio Usero and Dyas Utomo and Alberto Bolatto and M{\'e}lanie Chevance and Chris Faesi and Glover, \{Simon C.O.\} and Kepley, \{Amanda A.\} and Kruijssen, \{J. M.Diederik\} and Krumholz, \{Mark R.\} and Meidt, \{Sharon E.\} and Meier, \{David S.\} and Eric Murphy and Miguel Querejeta and Erik Rosolowsky and Toshiki Saito and Andreas Schruba",

year = "2018",

month = dec,

day = "1",

doi = "10.3847/2041-8213/aaf16a",

language = "English",

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Gallagher, MJ, Leroy, AK, Bigiel, F, Cormier, D, Jiménez-Donaire, MJ, Hughes, A, Pety, J, Schinnerer, E, Sun, J, Usero, A, Utomo, D, Bolatto, A, Chevance, M, Faesi, C, Glover, SCO, Kepley, AA, Kruijssen, JMD, Krumholz, MR, Meidt, SE, Meier, DS, Murphy, E, Querejeta, M, Rosolowsky, E, Saito, T & Schruba, A 2018, 'Do Spectroscopic Dense Gas Fractions Track Molecular Cloud Surface Densities?', Astrophysical Journal Letters, vol. 868, no. 2, L38. https://doi.org/10.3847/2041-8213/aaf16a