Studies of Regular and Random Magnetic Fields in the ISM: Statistics of Polarization Vectors and the Chandrasekhar-Fermi Technique

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

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Polarimetry is extensively used as a tool to trace the interstellar magnetic field projected on the plane of sky. Moreover, it is also possible to estimate the magnetic field intensity from polarimetric maps based on the Chandrasekhar-Fermi method. In this work, we present results for turbulent, isothermal, three-dimensional simulations of sub/supersonic and sub/super-Alfvénic cases. With the cubes, assuming perfect grain alignment, we created synthetic polarimetric maps for different orientations of the mean magnetic field with respect to the line of sight (LOS). We show that the dispersion of the polarization angle depends on the angle of the mean magnetic field regarding the LOS and on the Alfvénic Mach number. However, the second-order structure function of the polarization angle follows the relation SF ∝ lα, α being dependent exclusively on the Alfvénic Mach number. The results show an anticorrelation between the polarization degree and the column density, with exponent γ ∼ − 0.5, in agreement with observations, which is explained by the increase in the dispersion of the polarization angle along the LOS within denser regions. However, this effect was observed exclusively on supersonic, but sub-Alfvénic, simulations. For the super-Alfvénic, and the subsonic model, the polarization degree showed to be independent of the column density. Our major quantitative result is a generalized equation for the CF method, which allowed us to determine the magnetic field strength from the polarization maps with errors <20%. We also account for the role of observational resolution on the CF method.

Subfields: Astronomy and Astrophysics

View Paper: https://www.semanticscholar.org/paper/3bd45a199a96b373c20aca5805da549b00b7d00d

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In Astronomy and Astrophysics

1. A. Banday
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Citations in the corpus

• DENSITY STUDIES OF MHD INTERSTELLAR TURBULENCE: STATISTICAL MOMENTS, CORRELATIONS AND BISPECTRUM (2008, methodology): “Similar examples of simulation scaling can also be found in Falceta-Gonçalves et al.(2008).”
• 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.…”
• Planck intermediate results: XXXV. Probing the role of the magnetic field in the formation of structure in molecular clouds (2015, unknown): “Falceta-Gonc¸alves et al. (2008) propose a method that is potentially valid for any value of ς ψ , based on a fit to the B DCF ⊥ values obtained from maps at di ff erent resolutions, again concluding that the field should be lower than estimated with Eq.”
• Planck intermediate results. XIX. An overview of the polarized thermal emission from Galactic dust (2014, background): “It provides important information on the magnetic field distribution and orientation (see, e.g., Falceta-Gonçalves et al. 2008; Poidevin et al. 2013).”