The Universality of Turbulence in Galactic Molecular Clouds

Heyer, M. H.; Brunt, Christopher M.

doi:10.1086/425978

Cited by 457 publications

(547 citation statements)

References 26 publications

(42 reference statements)

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“…High mass clumps have velocity dispersions in the range 0.5 to 0.8 km s −1 . Compared to the observed distribution of Heyer & Brunt (2004), the clumps measured here appear to have lower velocity dispersions for their sizes. Velocity dispersions are underestimated by a factor of 2.8 ± 0.67 compared to the scaling law of Larson (1981) and 2.68 ± 0.63 compared to the scaling law of Solomon et al (1987).…”

Section: Clumpscontrasting

confidence: 77%

Magnetohydrodynamical simulation of the formation of clumps and filaments in quiescent diffuse medium by thermal instability

Wareing

Pittard

Falle

et al. 2016

Mon. Not. R. Astron. Soc.

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We have used the AMR hydrodynamic code, MG, to perform idealised 3D MHD simulations of the formation of clumpy and filamentary structure in a thermally unstable medium without turbulence. A stationary thermally unstable spherical diffuse atomic cloud with uniform density in pressure equilibrium with low density surroundings was seeded with random density variations and allowed to evolve. A range of magnetic field strengths threading the cloud have been explored, from β = 0.1 to β = 1.0 to the zero magnetic field case (β = ∞), where β is the ratio of thermal pressure to magnetic pressure. Once the density inhomogeneities had developed to the point where gravity started to become important, self-gravity was introduced to the simulation. With no magnetic field, clouds and clumps form within the cloud with aspect ratios of around unity, whereas in the presence of a relatively strong field (β = 0.1) these become filaments, then evolve into interconnected corrugated sheets that are predominantly perpendicular to the magnetic field. With magnetic and thermal pressure equality (β = 1.0), filaments, clouds and clumps are formed. At any particular instant, the projection of the 3D structure onto a plane parallel to the magnetic field, i.e. a line of sight perpendicular to the magnetic field, resembles the appearance of filamentary molecular clouds. The filament densities, widths, velocity dispersions and temperatures resemble those observed in molecular clouds. In contrast, in the strong field case β = 0.1, projection of the 3D structure along a line of sight parallel to the magnetic field reveals a remarkably uniform structure.

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Section: Clumpscontrasting

confidence: 77%

Magnetohydrodynamical simulation of the formation of clumps and filaments in quiescent diffuse medium by thermal instability

Wareing

Pittard

Falle

et al. 2016

Mon. Not. R. Astron. Soc.

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“…It has been used for studying the structure and scaling in several molecular cloud regions, simulations and synthetic images (Brunt & Heyer 2002a,b;Brunt et al 2003;Heyer & Brunt 2004;Heyer et al 2006). PCA can be used to characterise structure on different scales.…”

Section: Principal Component Analysismentioning

confidence: 99%

Comparing the statistics of interstellar turbulence in simulations and observations

Federrath

Duval

Klessen³

et al. 2010

A&A

808

101

1,286

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Context. Density and velocity fluctuations on virtually all scales observed with modern telescopes show that molecular clouds (MCs) are turbulent. The forcing and structural characteristics of this turbulence are, however, still poorly understood. Aims. To shed light on this subject, we study two limiting cases of turbulence forcing in numerical experiments: solenoidal (divergence-free) forcing and compressive (curl-free) forcing, and compare our results to observations. Methods. We solve the equations of hydrodynamics on grids with up to 1024 3 cells for purely solenoidal and purely compressive forcing. Eleven lower-resolution models with different forcing mixtures are also analysed. Results. Using Fourier spectra and Δ-variance, we find velocity dispersion-size relations consistent with observations and independent numerical simulations, irrespective of the type of forcing. However, compressive forcing yields stronger compression at the same rms Mach number than solenoidal forcing, resulting in a three times larger standard deviation of volumetric and column density probability distributions (PDFs). We compare our results to different characterisations of several observed regions, and find evidence of different forcing functions. Column density PDFs in the Perseus MC suggest the presence of a mainly compressive forcing agent within a shell, driven by a massive star. Although the PDFs are close to log-normal, they have non-Gaussian skewness and kurtosis caused by intermittency. Centroid velocity increments measured in the Polaris Flare on intermediate scales agree with solenoidal forcing on that scale. However, Δ-variance analysis of the column density in the Polaris Flare suggests that turbulence is driven on large scales, with a significant compressive component on the forcing scale. This indicates that, although likely driven with mostly compressive modes on large scales, turbulence can behave like solenoidal turbulence on smaller scales. Principal component analysis of G216-2.5 and most of the Rosette MC agree with solenoidal forcing, but the interior of an ionised shell within the Rosette MC displays clear signatures of compressive forcing. Conclusions. The strong dependence of the density PDF on the type of forcing must be taken into account in any theory using the PDF to predict properties of star formation. We supply a quantitative description of this dependence. We find that different observed regions show evidence of different mixtures of compressive and solenoidal forcing, with more compressive forcing occurring primarily in swept-up shells. Finally, we emphasise the role of the sonic scale for protostellar core formation, because core formation close to the sonic scale would naturally explain the observed subsonic velocity dispersions of protostellar cores.

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“…The irregular shapes of molecular clouds and their complex emission line profiles indicate that the gas motions are supersonic and vigorously turbulent [Heyer and Brunt, 2004]. Supersonic turbulence produces localised structures such as shocks and clumps which are amplified by gravity and cooling instabilities.…”

Section: Introductionmentioning

confidence: 99%

Star Formation in the Turbulent Interstellar Medium and Its Implications on Galaxy Evolution

Schmidt

Maier²,

Hupp³

et al.

High Performance Computing in Science and Engineering, Garching/Munich 2007

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The Universality of Turbulence in Galactic Molecular Clouds

Cited by 457 publications

References 26 publications

Magnetohydrodynamical simulation of the formation of clumps and filaments in quiescent diffuse medium by thermal instability

Magnetohydrodynamical simulation of the formation of clumps and filaments in quiescent diffuse medium by thermal instability

Comparing the statistics of interstellar turbulence in simulations and observations

Star Formation in the Turbulent Interstellar Medium and Its Implications on Galaxy Evolution

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