DAMPING OF MAGNETOHYDRODYNAMIC TURBULENCE IN PARTIALLY IONIZED GAS AND THE OBSERVED DIFFERENCE OF VELOCITIES OF NEUTRALS AND IONS

D. Falceta-Goncalves*, A. Lazarian, M. Houde

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

27 Citations (Scopus)

Abstract

Theoretical and observational studies on the turbulence of the interstellar medium developed fast in the past decades. The theory of supersonic magnetized turbulence, as well as the understanding of the projection effects of observed quantities, is still in progress. In this work, we explore the characterization of the turbulent cascade and its damping from observational spectral line profiles. We address the difference of ion and neutral velocities by clarifying the nature of the turbulence damping in the partially ionized. We provide theoretical arguments in favor of the explanation of the larger Doppler broadening of lines arising from neutral species compared to ions as arising from the turbulence damping of ions at larger scales. Also, we compute a number of MHD numerical simulations for different turbulent regimes and explicit turbulent damping, and compare both the three-dimensional distributions of velocity and the synthetic line profile distributions. From the numerical simulations, we place constraints on the precision with which one can measure the three-dimensional dispersion depending on the turbulence sonic Mach number. We show that no universal correspondence between the three-dimensional velocity dispersions measured in the turbulent volume and minima of the two-dimensional velocity dispersions available through observations exist. For instance, for subsonic turbulence the correspondence is poor at scales much smaller than the turbulence injection scale, while for supersonic turbulence the correspondence is poor for the scales comparable with the injection scale. We provide a physical explanation of the existence of such a two-dimensional to three-dimensional correspondence and discuss the uncertainties in evaluating the damping scale of ions that can be obtained from observations. However, we show that the statistics of velocity dispersion from observed line profiles can provide the spectral index and the energy transfer rate of turbulence. Also, by comparing two similar simulations with different viscous coefficients, it was possible to constrain the turbulent cut-off scale. This may especially prove useful since it is believed that ambipolar diffusion may be one of the dominant dissipative mechanisms in star-forming regions. In this case, the determination of the ambipolar diffusion scale may be used as a complementary method for the determination of magnetic field intensity in collapsing cores. We discuss the implications of our findings in terms of a new approach to magnetic field measurement proposed by Li & Houde.

Original languageEnglish
Pages (from-to)1376-1385
Number of pages10
JournalAstrophysical Journal
Volume713
Issue number2
DOIs
Publication statusPublished - 20 Apr 2010

Keywords

  • ISM: kinematics and dynamics
  • ISM: magnetic fields
  • methods: numerical
  • methods: statistical
  • techniques: radial velocities
  • MAGNETIC-FIELD STRUCTURE
  • STAR-FORMATION
  • INTERSTELLAR TURBULENCE
  • MOLECULAR CLOUD
  • MHD TURBULENCE
  • RECONNECTION
  • POLARIZATION
  • STATISTICS
  • SPECTRA
  • DENSITY

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