DENSITY STUDIES OF MHD INTERSTELLAR TURBULENCE: STATISTICAL MOMENTS, CORRELATIONS AND BISPECTRUM

By B. Burkhart, Diego Falceta-Gonçalves, Grzegorz Kowal, A. Lazarian. 2008

158 citations recorded by the source corpus.

We present a number of statistical tools that show promise for obtaining information on turbulence in molecular clouds (MCs) and diffuse interstellar medium (ISM). For our tests we make use of three-dimensional 5123 compressible MHD isothermal simulations performed for different sonic, i.e., , where VL is the injection velocity, Vs is the sound velocity, and Alfvénic , where VA is the Alfvén velocity, Mach numbers. We introduce the bispectrum, a new tool for statistical studies of the interstellar medium which, unlike an ordinary power spectrum of turbulence, preserves the phase information of the stochastic field. We show that the bispectra of the three-dimensional stochastic density field and of column densities, available from observations, are similar. This opens good prospects for studies of MCs and diffuse media with the new tool. We use the bispectrum technique to define the role of nonlinear wave–wave interactions in the turbulent energy cascade. We also obtained the bispectrum function for density and column densities with varying magnetic field strength. As expected, a strong correlation is obtained for wave modes k1 = k2 for all models. Larger values of result in increased correlations for modes with k1 ≠ k2. This effect becomes more evident with increasing magnetic field intensity. We believe that the different MHD wave modes, e.g., Alfvén and magneto-acoustic, which arise in strongly magnetized turbulence, may be responsible for the increased correlations compared to purely hydrodynamical perturbations. In addition to the bispectrum, we calculated the third and fourth statistical moments of density and column density, namely, skewness and kurtosis, respectively. We found a strong dependence of skewness and kurtosis with . In particular, as increases, so does the Gaussian asymmetry of the density distribution. We also studied the correlations of two-dimensional column density with dispersion of velocities and magnetic field, as well as the correlations of three-dimensional density with magnetic and kinetic energy and for comparison. Our results show that column density is linearly correlated with magnetic field for high . This trend is independent of the turbulent kinetic energy and can be used to characterize inhomogeneities of physical properties in low density clumps in the ISM.

Subfields: Astronomy and Astrophysics, Atomic and Molecular Physics, and Optics

View Paper: https://www.semanticscholar.org/paper/bdd835a7b85b42538e64bb63a362c25528155645

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Citations in the corpus

AN IMPRINT OF MOLECULAR CLOUD MAGNETIZATION IN THE MORPHOLOGY OF THE DUST POLARIZED EMISSION (2013, background): “…structures along the magnetic field lines when the medium is strongly compressed supersonically (Ostriker et al. 2001; Heitsch et al. 2001; Falceta-Gonçalves et al. 2008), and linear correlation of the magnetic field strength with column density for supersonic turbulence (Burkhart et al. 2009).”
THE STAR FORMATION RATE OF TURBULENT MAGNETIZED CLOUDS: COMPARING THEORY, SIMULATIONS, AND OBSERVATIONS (2012, background): “…turbulence (Vázquez-Semadeni 1994), intermittency introduces skewness and kurtosis in the distributions (Klessen 2000; Kritsuk et al. 2007; Burkhart et al. 2009), which becomes stronger for more compressive forcing (Schmidt et al. 2009; Federrath et al. 2010b) and for higher Mach numbers…”
An improved map of the Galactic Faraday sky (2011, background): “…more realistic study will likely have to involve numerical magneto-hydrodynamical simulations of the interstellar medium, which have become more and more sophisticated over the last years (see e.g. de Avillez & Breitschwerdt 2007; Kissmann et al. 2008; Burkhart et al. 2009; Tofflemire et al. 2011).”
ON THE STAR FORMATION EFFICIENCY OF TURBULENT MAGNETIZED CLOUDS (2012, background): “Moreover, if an independent estimate of the sonic Mach number is available (e.g., Burkhart et al. 2009) and if the forcing can be constrained (Brunt et al. 2010b,a; Brunt 2010; Konstandin et al. 2012b; Kainulainen & Tan 2012; Seon 2012), measuring α and comparing it with the present set of…”
Turbulent molecular clouds (2012, methodology): “In the context of polytropic flows, the weakness of the correlation has been interpreted by Passot & Vazquez-Semadeni (2003) (see also Burkhart et al. 2009) in terms of the fact that the various types of (nonlinear, or simple) MHD wave are characterized by different scalings of the field strength…”