The Kennicutt-Schmidt Law and Gas Scale Height in Luminous and Ultraluminous Infrared Galaxies

A new analysis of high-resolution data from the Atacama Large Millimeter/submillimeter Array for five luminous or ultraluminous infrared galaxies gives a slope for the Kennicutt-Schmidt (KS) relation equal to for gas surface densities mol > 103 M pc−2 and an assumed constant CO-to-H2 conversion f...

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Bibliographic Details
Published in:The Astrophysical journal 2019-09, Vol.882 (1), p.5
Main Authors: Wilson, Christine D., Elmegreen, Bruce G., Bemis, Ashley, Brunetti, Nathan
Format: Article
Language:English
Subjects:
Astrophysics
Computer simulation
Density
Depletion
Empirical analysis
Feedback
Galaxies
Infrared analysis
Infrared astronomy
Infrared galaxies
Interstellar medium
Radio telescopes
Scale height
Slopes
Star & galaxy formation
Star formation
Starburst galaxies
Stars & galaxies
Turbulence
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Summary:A new analysis of high-resolution data from the Atacama Large Millimeter/submillimeter Array for five luminous or ultraluminous infrared galaxies gives a slope for the Kennicutt-Schmidt (KS) relation equal to for gas surface densities mol > 103 M pc−2 and an assumed constant CO-to-H2 conversion factor. The velocity dispersion of the CO line, v, scales approximately as the inverse square root of mol, making the empirical gas scale height determined from nearly constant, 150-190 pc, over 1.5 orders of magnitude in mol. This constancy of H implies that the average midplane density, which is presumably dominated by CO-emitting gas for these extreme star-forming galaxies, scales linearly with the gas surface density, which in turn implies that the gas dynamical rate (the inverse of the freefall time) varies with , thereby explaining most of the super-linear slope in the KS relation. Consistent with these relations, we also find that the mean efficiency of star formation per freefall time is roughly constant, 5%-7%, and the gas depletion time decreases at high mol, reaching only ∼16 Myr at mol ∼ 104 M pc−2. The variation of v with mol and the constancy of H are in tension with some feedback-driven models, which predict v to be more constant and H to be more variable. However, these results are consistent with simulations in which large-scale gravity drives turbulence through a feedback process that maintains an approximately constant Toomre Q instability parameter.
ISSN:0004-637X
1538-4357
1538-4357
DOI:10.3847/1538-4357/ab31f3