On Scaling Laws and Alfvenic Magnetic Fluctuations in Molecular Clouds

Abstract

Under the basic assumption that the observed turbulent motions in molecular clouds are Alfvenic waves or turbulence, we emphasize that the Doppler broadening of molecular line profiles directly measures the velocity amplitudes of the waves instead of the Alfven velocity. Assuming an equipartition between the kinetic energy and the Alfvenic magnetic energy, we further propose the hypothesis that observed standard scaling laws in molecular clouds imply a roughly scale-independent fluctuating magnetic field, which might be understood as a result of strong wave-wave interactions and subsequent energy cascade. We predict that ${\sigma }_v\propto {\rho }^{-0.5}$ is a more basic and robust relation in that it may approximately hold in any regions where the spatial energy density distribution is primarily determined by wave-wave interactions, including gravitationally unbound regions. We also discuss the fact that a scale-independent ${\sigma }_B^2$ appears to contradict existing 1-D and 2-D computer simulations of MHD turbulence in molecular clouds.

11 pages, to appear in Astrophysical Journal Letters, email: [email protected]

References in corpus (4)

• Dense Gas and Star Formation: Characteristics of Cloud Cores Associated with Water Masers
• A Turbulent Model for the Interstellar Medium. II. Magnetic Fields and Rotation
• A Search for Larson-Type Relations in Numerical Simulations of the ISM. Evidence for Non-Constant Column Densities
• Can Nonlinear Hydromagnetic Waves Support a Self-Gravitating Cloud?

Cited by in corpus (6)

• Interstellar Turbulence I: Observations and Processes
• A Super-Alfvenic Model of Dark Clouds
• Synthetic Molecular Clouds from Supersonic MHD and Non-LTE Radiative Transfer Calculations
• Formation and loss of hierarchical structure in two-dimensional MHD simulations of wave-driven turbulence in interstellar clouds
• A Prescription for Star Formation Feedback: The Importance of Multiple Shell Interactions
• Energy Budget and the Virial Theorem in Interstellar Clouds