Density Fluctuations in MHD Turbulence: Spectra, Intermittency, and Topology

By Grzegorz Kowal, A. Lazarian, A. Beresnyak. 2006

232 citations recorded by the source corpus.

We perform three-dimensional (3D) compressible MHD simulations over many dynamical times for an extended range of sonic and Alfvén Mach numbers and analyze the statistics of 3D density and 2D column density, which include probability distribution functions, spectra, skewness, kurtosis, She-Lévêque exponents, and genus. In order to establish the relation between the statistics of the observables, i.e., column densities, and the underlying 3D statistics of density, we analyze the effects of cloud boundaries. We define the parameter space for 3D measures to be recovered from column densities. In addition, we show that for subsonic turbulence the spectra of density fluctuations are consistent with k-7/3 in the case of a strong magnetic field and k-5/3 in the case of a weak magnetic field. For supersonic turbulence we confirm the earlier findings of the shallow spectra of density and Kolmogorov spectra of the logarithm of density. We find that the intermittencies of the density and velocity are very different.

Subfields: Astronomy and Astrophysics, Computational Mechanics

View Paper: https://www.semanticscholar.org/paper/57bc8947154e7ba821551e774c9307bbe5d0c85c

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In Computational Mechanics

Citations in the corpus

NUMERICAL TESTS OF FAST RECONNECTION IN WEAKLY STOCHASTIC MAGNETIC FIELDS (2009, methodology): “Supported by our studies of turbulence (see Kowal et al 2007; Kowal & Lazarian 2007) where we used similar code, we estimated the dissipation scale kν ≈ 30 for the resolution of models presented here.”
THE FRACTAL DENSITY STRUCTURE IN SUPERSONIC ISOTHERMAL TURBULENCE: SOLENOIDAL VERSUS COMPRESSIVE ENERGY INJECTION (2007, result): “Our estimates of density spectra for solenoidal forcing are in agreement with previous studies, e.g., the weakly magnetized super-Alfvénic supersonic MHD models by Padoan et al. (2004a) and Kowal et al. (2007), and consistent with the hydrodynamic estimates by Kritsuk et al. (2006).”
Studies of Regular and Random Magnetic Fields in the ISM: Statistics of Polarization Vectors and the Chandrasekhar-Fermi Technique (2008, methodology): “As an example, simulations have shown that strongly magnetized turbulent media develop structures with lower density contrasts when compared to pure hydrodynamic turbulence (Kowal et al. 2007; Kritsuk et al. 2007).”
The warm ionized medium in spiral galaxies (2009, background): “Data also suggest that the filling fraction increases from f ∼ 0.1 at the midplane to f > 0.3– 0.4 at |z| = 1000 pc (Berkhuijsen et al., 2006; Gaensler et al., 2008; Kulkarni and Heiles, 1987; Reynolds, 1991b).”
ON THE STAR FORMATION EFFICIENCY OF TURBULENT MAGNETIZED CLOUDS (2012, result): “All density spectra in Figures 7 and 8 are broadly consistent with previous studies exploring a limited subset of the parameter space analyzed in this study (Beresnyak et al. 2005; Kowal et al. 2007; Kritsuk et al. 2007; Federrath et al. 2009; Collins et al. 2012).”
EXTENDING THE BIG POWER LAW IN THE SKY WITH TURBULENCE SPECTRA FROM WISCONSIN Hα MAPPER DATA (2009, methodology): “This question was addressed by Hill et al. (2008), who compared the PDFs obtained via MHD simulations in Kowal et al. (2007) and the PDFs of WHAM data.”