Direct Evidence for Two-Fluid Effects in Molecular Clouds

Abstract

We present a combination of theoretical and simulation-based examinations of the role of two-fluid ambipolar drift on molecular line widths. The dissipation provided by ion-neutral interactions can produce a significant difference between the widths of neutral molecules and the widths of ionic species, comparable to the sound speed. We demonstrate that Alfven waves and certain families of magnetosonic waves become strongly damped on scales comparable to the ambipolar diffusion scale. Using the RIEMANN code, we simulate two-fluid turbulence with ionization fractions ranging from 10^{-2} to 10^{-6}. We show that the wave damping causes the power spectrum of the ion velocity to drop below that of the neutral velocity when measured on a relative basis. Following a set of motivational observations by Li & Houde (2008), we produce synthetic line width-size relations that shows a difference between the ion and neutral line widths, illustrating that two-fluid effects can have an observationally detectable role in modifying the MHD turbulence in the clouds.

18 pages, 4 figures, submitted to MNRAS

References in corpus (7)

• Cold Dark Clouds: The Initial Conditions for Star Formation
• Testing Magnetic Star Formation Theory
• Probing the Turbulence Dissipation Range and Magnetic Field Strengths in Molecular Clouds
• Sub-Alfvenic Non-Ideal MHD Turbulence Simulations with Ambipolar Diffusion: I. Turbulence Statistics
• Magnetically-Regulated Fragmentation Induced by Nonlinear Flows and Ambipolar Diffusion
• A three-dimensional numerical method for modelling weakly ionized plasmas
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Cited by in corpus (17)

• Dispersion of Magnetic Fields in Molecular Clouds. I
• The Dynamics of Massive Starless Cores with ALMA
• Dispersion of Magnetic Fields in Molecular Clouds. III
• Alfvenic Turbulence Beyond the Ambipolar Diffusion Scale
• Linewidth Differences of Neutrals and Ions Induced by MHD Turbulence
• Non-Zeeman Circular Polarization of Molecular Rotational Spectral Lines
• Evidence for Dynamically Important Magnetic Fields in Molecular Clouds
• Probing the Turbulence Dissipation Range and Magnetic Field Strengths in Molecular Clouds. II. Directly Probing the Ion-neutral Decoupling Scale
• Probing the Turbulent Ambipolar Diffusion Scale in Molecular Clouds with Spectroscopy
• Sub-Alfvenic Non-Ideal MHD Turbulence Simulations with Ambipolar Diffusion: III. Implications for Observations and Turbulent Enhancement
• Observational Diagnostics for Two-Fluid Turbulence in Molecular Clouds As Suggested by Simulations
• Turbulent dynamo in a weakly ionized medium
• Characterization of Turbulence from Submillimeter Dust Emission
• Two-dimensional partially ionized magnetohydrodynamic turbulence
• Magnetic Fields in Molecular Clouds -- Observation and Interpretation
• Molecular Line Emission from Multifluid Shock Waves. I. Numerical Methods and Benchmark Tests
• CO Structures with Narrow Lines in Nearby Quiescent Regions