Velocity Anisotropy as a Diagnostic of the Magnetization of the Interstellar Medium and Molecular Clouds

We use a set of magnetohydrodynamic simulations of fully developed (driven) turbulence to study the anisotropy in the velocity field that is induced by the presence of the magnetic field. In our models, we study turbulence characterized by sonic Mach numbers Ms from 0.7 to 7.5 and Alfven Mach number...

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Vydáno v:The Astrophysical journal Ročník 740; číslo 2; s. 117 - jQuery1323902623958='48'
Hlavní autoři: Esquivel, A, Lazarian, A
Médium: Journal Article
Jazyk:angličtina
Vydáno: Bristol IOP Publishing 20.10.2011
IOP
Témata:
Astronomy
Earth, ocean, space
Exact sciences and technology
Magnetohydrodynamics
Turbulence
Magnetization
Molecular clouds
Structure functions
Model study
Velocity fields
ISM: structure
radio lines: ISM
Anisotropy
White noise
Density fluctuation
ISM: general
Magnetic fields
magnetohydrodynamics (MHD)
Interstellar matter
Mach number
ISSN:0004-637X, 1538-4357
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Shrnutí:We use a set of magnetohydrodynamic simulations of fully developed (driven) turbulence to study the anisotropy in the velocity field that is induced by the presence of the magnetic field. In our models, we study turbulence characterized by sonic Mach numbers Ms from 0.7 to 7.5 and Alfven Mach numbers from 0.4 to 7.7. These are used to produce synthetic observations (centroid maps) that are then analyzed. To study the effect of large-scale density fluctuations and of white noise, we have modified the density fields and obtained new centroid maps, which are analyzed. We show that restricting the range of scales at which the anisotropy is measured makes the method robust against such fluctuations. We show that the anisotropy in the structure function of the maps reveals the direction of the magnetic field for MA 1.5, regardless of the sonic Mach number. We find that the degree of anisotropy can be used to determine the degree of magnetization (i.e., MA ) for MA 1.5. To do this, one needs an additional measure of the sonic Mach number and an estimate of the line of sight magnetic field, both feasible by other techniques, offering a new opportunity to study the magnetization state of the interstellar medium.
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USDOE Office of Science (SC), Fusion Energy Sciences (FES)
ISSN:0004-637X
1538-4357
DOI:10.1088/0004-637X/740/2/117