Dense Gas, Dynamical Equilibrium Pressure, and Star Formation in Nearby Star-forming Galaxies

Gallagher, Molly; Leroy, Adam K.; Bigiel, Frank; Cormier, D.; Jiménez-Donaire, María J.; Ostriker, Eve C.; Usero, A.; Bolatto, Alberto D.; García‐Burillo, S.; Hughes, Annie; Kepley, Amanda A.; Krumholz, Mark R.; Meidt, Sharon E.; Meier, David S.; Murphy, E. J.; Pety, J.; Rosolowsky, Erik; Schinnerer, E.; Schruba, Andreas; Walter, Fabian

doi:10.3847/1538-4357/aabad8

Cited by 105 publications

(181 citation statements)

References 116 publications

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“…The lines in the plots are Local Polynomial Regression fits only to guide the eye, which is similar to the binning method used in many other studies, and they do not strongly suggest that our data points closely follow those fits. This is consistent with Usero et al (2015) and the larger galaxy sample compiled by Gallagher et al (2018a), where they show a very weak correlation (ρ sp = 0.13) and a large scatter about the relationships, and they suggest that the HCN/CO ratio is a relatively poor predictor of SFE mol . Our plot shows a similar case using high-J dense molecular lines, implying that the SFE, if measured as SFR per unit total molecular gas (SFE mol ) is rather independent of the dense-gas fraction ( f dense ) that is measured with the J = 4−3 transition.…”

Section: The Relationships Between Star-formation Efficiency Dense-gsupporting

confidence: 86%

“…This is likely due to our limited data for only one galaxy, and the variation of f dense is large, especially in the log 10 Σ stellar range between 2.5 and 3. If we compare our data points with previous studies (Gallagher et al 2018a;Usero et al 2015), they seem to lie in a similar range in the plot, though we are using high-J lines.…”

Section: The Relationships Between Star-formation Efficiency Dense-gsupporting

confidence: 53%

“…With regard to the relationship between SFE dense and Σ stellar , previous studies using the J = 1 − 0 transition of HCN and/or HCO + all showed anti-correlations (Usero et al 2015;Gallagher et al 2018a;Jiménez-Donaire et al 2019), so it is somewhat surprising to see an increasing trend between SFE dense and Σ stellar in Fig. 11b.…”

Section: The Relationships Between Star-formation Efficiency Dense-gmentioning

confidence: 83%

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The MALATANG survey: dense gas and star formation from high-transition HCN and HCO+ maps of NGC 253

Jiang

Greve

Gao

et al. 2020

Monthly Notices of the Royal Astronomical Society

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To study the high-transition dense-gas tracers and their relationships to the star formation of the inner ∼ 2 kpc circumnuclear region of NGC 253, we present HCN J = 4 − 3 and HCO + J = 4 − 3 maps obtained with the James Clerk Maxwell Telescope (JCMT). With the spatially resolved data, we compute the concentration indices r 90 /r 50 for the different tracers. HCN and HCO + 4-3 emission features tend to be centrally concentrated, which is in contrast to the shallower distribution of CO 1-0 and the stellar component. The dense-gas fraction ( f dense , traced by the velocity-integratedintensity ratios of HCN/CO and HCO + /CO) and the ratio R 31 (CO 3-2/1-0) decline towards larger galactocentric distances, but increase with higher SFR surface density. The radial variation and the large scatter of f dense and R 31 imply distinct physical conditions in different regions of the galactic disc. The relationships of f dense versus Σ stellar , and SFE dense versus Σ stellar are explored. SFE dense increases with higher Σ stellar in this galaxy, which is inconsistent with previous work that used HCN 1-0 data. This implies that existing stellar components might have different effects on the high-J HCN and HCO + than their low-J emission. We also find that SFE dense seems to be decreasing with higher f dense which is consistent with previous works, and it suggests that the ability of the dense gas to form stars diminishes when the average density of the gas increases. This is expected in a scenario where only the regions with high-density contrast collapse and form stars.

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Section: The Relationships Between Star-formation Efficiency Dense-gsupporting

confidence: 86%

Section: The Relationships Between Star-formation Efficiency Dense-gsupporting

confidence: 53%

Section: The Relationships Between Star-formation Efficiency Dense-gmentioning

confidence: 83%

See 1 more Smart Citation

The MALATANG survey: dense gas and star formation from high-transition HCN and HCO+ maps of NGC 253

Jiang

Greve

Gao

et al. 2020

Monthly Notices of the Royal Astronomical Society

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“…Momose et al (2010) measured the star formation efficiency (SFE = Σ SFR /Σ H 2 ) in a barred galaxy of NGC 4303 at a spatial resolution of 500 pc and reported that the SFEs in the arm regions are about two times higher than those in the bar regions (see also Yajima E-mail: fmaeda@kusastro.kyoto-u.ac.jp et al 2019). Such variations of the SFE with environments are reported for other nearby galaxies and the Milky Way (e.g., Watanabe et al 2011;Leroy et al 2013;Longmore et al 2013;Hirota et al 2014;Usero et al 2015;Gallagher et al 2018), but physical mechanism which controls the SFE within galaxies is still unclear.…”

Section: Introductionmentioning

confidence: 81%

Properties of giant molecular clouds in the strongly barred galaxy NGC 1300

Maeda

Ohta

Fujimoto

et al. 2020

Monthly Notices of the Royal Astronomical Society

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Star formation activity depends on galactic-scale environments. To understand the variations in star formation activity, comparing the properties of giant molecular clouds (GMCs) among environments with different star formation efficiency (SFE) is necessary. We thus focus on a strongly barred galaxy to investigate the impact of the galactic environment on the GMCs properties, because the SFE is clearly lower in bar regions than in arm regions. In this paper, we present the 12 CO(1 − 0) observations toward the western bar, arm and bar-end regions of the strongly barred galaxy NGC 1300 with ALMA 12-m array at a high angular resolution of ∼40 pc. We detected GMCs associated with the dark lanes not only in the arm and bar-end regions but also in the bar region, where massive star formation is not seen. Using the CPROPS algorithm, we identified and characterized 233 GMCs across the observed regions. Based on the Kolmogorov-Smirnov test, we find that there is virtually no significant variations in GMC properties (e.g., radius, velocity dispersion, molecular gas mass, and virial parameter) among the bar, arm and bar-end region. These results suggest that systematic differences in the physical properties of the GMCs are not the cause for SFE differences with environments, and that there should be other mechanisms which control the SFE of the GMCs such as fast cloud-cloud collisions in NGC 1300.

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“…A model of gas self-gravity and orbital motions throughout galaxies The cloud-scale measurements needed to examine how several of the parameters in our model of star formation are related and how they vary together throughout the disks of real star-forming galaxies, are currently being assembled by the PHANGS collaboration (A. K. Leroy et al, in prep. ; see also Gallagher et al 2018a;Sun et al 2018;Utomo et al 2018;Chevance et al 2019;P. Lang et al, ApJ subm.…”

Section: Bottleneck Using Semi-empirical Cloud and Galaxy Modelsmentioning

confidence: 94%

A Model for the Onset of Self-gravitation and Star Formation in Molecular Gas Governed by Galactic Forces. II. The Bottleneck to Collapse Set by Cloud–Environment Decoupling

Meidt

Glover

Kruijssen

et al. 2020

ApJ

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In Meidt et al. (2018), we showed that gas kinematics on the scale of individual molecular clouds are not dominated by self-gravity but also track a component that originates with orbital motion in the potential of the host galaxy. This agrees with observed cloud line widths, which show systematic variations from virial motions with environment, pointing at the influence of the galaxy potential. In this paper, we hypothesize that these motions act to slow down the collapse of gas and so help regulate star formation. Extending the results of Meidt et al. (2018), we derive a dynamical collapse timescale that approaches the free-fall time only once the gas has fully decoupled from the galactic potential. Using this timescale we make predictions for how the fraction of free-falling, strongly self-gravitating gas varies throughout the disks of star-forming galaxies. We also use this collapse timescale to predict variations in the molecular gas star formation efficiency, which is lowered from a maximum, feedback-regulated level in the presence of strong coupling to the galactic potential. Our model implies that gas can only decouple from the galaxy to collapse and efficiently form stars deep within clouds. We show that this naturally explains the observed drop in star formation rate per unit gas mass in the Milky Way's CMZ and other galaxy centers. The model for a galactic bottleneck to star formation also agrees well with resolved observations of dense gas and star formation in galaxy disks and the properties of local clouds.

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Dense Gas, Dynamical Equilibrium Pressure, and Star Formation in Nearby Star-forming Galaxies

Cited by 105 publications

References 116 publications

The MALATANG survey: dense gas and star formation from high-transition HCN and HCO+ maps of NGC 253

The MALATANG survey: dense gas and star formation from high-transition HCN and HCO+ maps of NGC 253

Properties of giant molecular clouds in the strongly barred galaxy NGC 1300

A Model for the Onset of Self-gravitation and Star Formation in Molecular Gas Governed by Galactic Forces. II. The Bottleneck to Collapse Set by Cloud–Environment Decoupling

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