Studies of regular and random magnetic fields in the ISM: Statistics of polarization vectors and the Chandrasekhar-Fermi technique

Diego Falceta-Goncalves*, Alex Lazarian, Grzegorz Kowal

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

163 Citations (Scopus)

Abstract

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-Alfvenic 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 Alfvenic Mach number. However, the second-order structure function of the polarization angle follows the relation SF alpha l(alpha), alpha being dependent exclusively on the Alfvenic Mach number. The results show an anticorrelation between the polarization degree and the column density, with exponent gamma similar to -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-Alfvenic, simulations. For the super-Alfvenic, 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

Original languageEnglish
Pages (from-to)537-551
Number of pages15
JournalAstrophysical Journal
Volume679
Issue number1
Publication statusPublished - 20 May 2008

Keywords

  • ISM : magnetic fields
  • methods : numerical
  • methods : statistical
  • techniques : polarimetric
  • FAR-INFRARED POLARIMETRY
  • MOLECULAR CLOUDS
  • GRAIN ALIGNMENT
  • RADIATIVE TORQUES
  • DUST EMISSION
  • SUBMILLIMETER POLARIZATION
  • INTERSTELLAR GRAINS
  • BASIC PROPERTIES
  • MHD TURBULENCE
  • DARK CLOUDS

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