Volumetric star formation laws of disc galaxies

Bacchini, Cecilia; Fraternali, Filippo; Iorio, Giuliano; Pezzulli, Gabriele

doi:10.1051/0004-6361/201834382

Cited by 116 publications

(143 citation statements)

References 88 publications

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“…From these we determine the average midplane density, free-fall time, gas consumption time, and efficiency per free-fall time. The results confirm the super-linear KS slope found previously for starbursts, and they also reveal a nearly constant disk thickness, confirming the most basic model in which three-dimensional density primarily determines the rate at which gas turns into stars (Madore 1977;Silk 1987;Katz 1992;Elmegreen 1994Elmegreen , 2002Krumholz & McKee 2005;Bacchini et al 2019;see review in Krumholz 2014).…”

Section: Introductionsupporting

confidence: 88%

“…Because the disk thickness and ff are much more constant than either Σ gas or ρ mid , integration over the thickness of the disk in starburst galaxies preserves the mathematical form of this law with the substitution of surface density for space density. This model is roughly similar in spiral galaxies, although it may be more complicated in the gas-dominated regions if the scale height varies significantly (e.g., Barnes et al 2012;Elmegreen & Hunter 2015;Elmegreen 2015;Bacchini et al 2019).…”

Section: Discussionmentioning

confidence: 99%

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

Wilson

Elmegreen

Bemis

et al. 2019

ApJ

118

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A new analysis of high-resolution data from the Atacama Large Millimeter/submillimeter Array (ALMA) for 5 luminous or ultra-luminous infrared galaxies gives a slope for the Kennicutt-Schmidt (KS) relation equal to 1.74 +0.09 −0.07 for gas surface densities Σ mol > 10 3 M pc −2 and an assumed constant CO-to-H 2 conversion factor. The velocity dispersion of the CO line, σ v , scales approximately as the inverse square root of Σ mol , making the empirical gas scale height determined from H ∼ 0.5σ 2 /(πGΣ mol ) nearly constant, 150-190 pc, over 1.5 orders of magnitude in Σ 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 free-fall time) varies with Σ 1/2 mol , 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 free-fall time is roughly constant, 5%-7%, and the gas depletion time decreases at high Σ mol , reaching only ∼ 16 Myr at Σ mol ∼ 10 4 M pc −2 . The variation of σ v with Σ mol and the constancy of H are in tension with some feedback-driven models, which predict σ 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.

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Section: Introductionsupporting

confidence: 88%

Section: Discussionmentioning

confidence: 99%

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

Wilson

Elmegreen

Bemis

et al. 2019

ApJ

118

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“…This peculiar kinematics, along with a significant thickness (1 < h < 3 kpc), imply that the EPG properties are not compatible with predictions based on hydrostatic equilibrium models (e.g. Barnabè et al 2006;Marinacci et al 2010b;Bacchini et al 2019). Nonstationary models are therefore required to explain the properties of this component.…”

Section: The Origin Of the Epgmentioning

confidence: 89%

HALOGAS: the properties of extraplanar HI in disc galaxies

Marasco

Fraternali

Heald

et al. 2019

A&A

128

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We present a systematic study of the extraplanar gas (EPG) in a sample of 15 nearby late-type galaxies at intermediate inclinations using publicly available, deep interferometric H I data from the HALOGAS survey. For each system we mask the H I emission coming from the regularly rotating disc and use synthetic datacubes to model the leftover 'anomalous' H I flux. Our model consists of a smooth, axisymmetric thick component described by 3 structural and 4 kinematical parameters, which are fit to the data via a Bayesian MCMC approach. We find that extraplanar H I is nearly ubiquitous in disc galaxies, as we fail to detect it in only two of the systems with the poorest spatial resolution. The EPG component encloses ∼ 5 − 25% of the total H I mass, with a mean value of 14%, and has a typical thickness of a few kpc, incompatible with expectations based on hydrostatic equilibrium models. The EPG kinematics is remarkably similar throughout the sample, and consists of a lagging rotation with typical vertical gradients of ∼ −10 km s −1 kpc −1 , a velocity dispersion of 15 − 30 km s −1 and, for most galaxies, a global inflow in both the vertical and radial directions with speeds of 20 − 30 km s −1 . The EPG H I masses are in excellent agreement with predictions from simple models of the galactic fountain powered by stellar feedback. The combined effect of photo-ionisation and interaction of the fountain material with the circumgalactic medium can qualitatively explain the kinematics of the EPG, but dynamical models of the galactic fountain are required to fully test this framework.

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“…This is an example of how magnetic fields can be used to indirectly probe other galactic properties. Flaring of galactic discs is expected on theoretical grounds [185,186], and has been observed in warm neutral (H I) gas in the Milky Way [187] and in other galaxies [121,188,189]. Flaring of the disc of warm ionized gas is not evident from observations in the Milky Way [120], and no data are available for external galaxies yet.…”

Section: Magnetic Pitch Angle From Dynamo Modelsmentioning

confidence: 99%

Synthesizing Observations and Theory to Understand Galactic Magnetic Fields: Progress and Challenges

et al. 2019

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Constraining dynamo theories of magnetic field origin by observation is indispensable but challenging, in part because the basic quantities measured by observers and predicted by modelers are different. We clarify these differences and sketch out ways to bridge the divide. Based on archival and previously unpublished data, we then compile various important properties of galactic magnetic fields for nearby spiral galaxies. We consistently compute strengths of total, ordered, and regular fields, pitch angles of ordered and regular fields, and we summarize the present knowledge on azimuthal modes, field parities, and the properties of non-axisymmetric spiral features called magnetic arms. We review related aspects of dynamo theory, with a focus on mean-field models and their predictions for large-scale magnetic fields in galactic discs and halos. Further, we measure the velocity dispersion of H I gas in arm and inter-arm regions in three galaxies, M 51, M 74, and NGC 6946, since spiral modulation of the root-mean-square turbulent speed has been proposed as a driver of non-axisymmetry in large-scale dynamos. We find no evidence for such a modulation and place upper limits on its strength, helping to narrow down the list of mechanisms to explain magnetic arms. Successes and remaining challenges of dynamo models with respect to explaining observations are briefly summarized, and possible strategies are suggested. With new instruments like the Square Kilometre Array (SKA), large data sets of magnetic and non-magnetic properties from thousands of galaxies will become available, to be compared with theory.

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Volumetric star formation laws of disc galaxies

Cited by 116 publications

References 88 publications

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

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

HALOGAS: the properties of extraplanar HI in disc galaxies

Synthesizing Observations and Theory to Understand Galactic Magnetic Fields: Progress and Challenges

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