Comparing the statistics of interstellar turbulence in simulations and observations - Solenoidal versus compressive turbulence forcing
Christoph Federrath,Christoph Federrath,Christoph Federrath,Julia Roman-Duval,Julia Roman-Duval,Ralf S. Klessen,Wolfgang Schmidt,Wolfgang Schmidt,Mordecai-Mark Mac Low,Mordecai-Mark Mac Low +9 more
TLDR
In this paper, the authors study two limiting cases of turbulence forcing in numerical experiments: solenoidal (divergence-free) forcing and compressive (curl-free), and compare their results to observations.Abstract:
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 10243 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.read more
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A new class of accurate, mesh-free hydrodynamic simulation methods
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Characterizing interstellar filaments with Herschel in IC 5146
Doris Arzoumanian,Ph. André,Pierre Didelon,Vera Könyves,Nicola Schneider,Alexander Men'shchikov,Thierry Sousbie,Annie Zavagno,Sylvain Bontemps,J. Di Francesco,Matthew Joseph Griffin,M. Hennemann,Tracey Hill,Jason M. Kirk,Peter G. Martin,Vincent Minier,Sergio Molinari,Frédérique Motte,Nicolas Peretto,Stefano Pezzuto,Luigi Spinoglio,Derek Ward-Thompson,Glenn J. White,Christine D. Wilson +23 more
TL;DR: In this paper, the results of the Herschel Gould Belt survey toward the IC 5146 molecular cloud were analyzed and a preliminary analysis of the filamentary structure in this region was presented.
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The Star Formation Rate of Turbulent Magnetized Clouds: Comparing Theory, Simulations, and Observations
TL;DR: In this paper, the role of turbulence and magnetic fields in star formation in molecular clouds is studied, and it is shown that the SFR depends on four basic parameters: (1) virial parameter αvir; (2) sonic Mach number ; (3) turbulent forcing parameter b, which is a measure for the fraction of energy driven in compressive modes; and (4) plasma with the Alfven Mach number.
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Herschel view of the Taurus B211/3 filament and striations: evidence of filamentary growth?
P. Palmeirim,Ph. André,Jason M. Kirk,Derek Ward-Thompson,Doris Arzoumanian,Vera Könyves,Vera Könyves,Pierre Didelon,Nicola Schneider,Nicola Schneider,M. Benedettini,Sylvain Bontemps,J. Di Francesco,J. Di Francesco,Davide Elia,Matthew Joseph Griffin,M. Hennemann,Tracey Hill,Peter G. Martin,Alexander Men'shchikov,Sergio Molinari,Frédérique Motte,Q. Nguyen Luong,David John Nutter,Nicolas Peretto,Stefano Pezzuto,A. Roy,Kazi L.J. Rygl,Luigi Spinoglio,G. L. White,G. L. White +30 more
TL;DR: In this article, the results from the Herschel Gould Belt survey for the B211/L1495 region in the Taurus molecular cloud were presented, which revealed the structure of the dense, star-forming filament B211 with unprecedented detail, along with the presence of striations perpendicular to the filament.
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TL;DR: In this article, the authors review the observational and theoretical knowledge of molecular clouds trying to confront the two approaches wherever possible, and emphasize the dynamical processes with special focus to turbulence and its impact on cloud evolution.
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