Statistical analysis of the mass-to-flux ratio in turbulent cores: effects of magnetic field reversals and dynamo amplification

Abstract

We study the mass-to-flux ratio (M/Φ) of clumps and cores in simulations of supersonic, magnetohydrodynamical turbulence for different initial magnetic field strengths. We investigate whether the (M/Φ)-ratio of core and envelope, R = (M/Φ)_{core}/(M/Φ)_{envelope} can be used to distinguish between theories of ambipolar diffusion and turbulence-regulated star formation. We analyse R for different Lines-of-Sight (LoS) in various sub-cubes of our simulation box. We find that, 1) the average and median values of |R| for different times and initial magnetic field strengths are typically greater, but close to unity, 2) the average and median values of |R| saturate at average values of |R| ~ 1 for smaller magnetic fields, 3) values of |R| < 1 for small magnetic fields in the envelope are caused by field reversals when turbulence twists the field lines such that field components in different directions average out. Finally, we propose two mechanisms for generating values |R| ~< 1 for the weak and strong magnetic field limit in the context of a turbulent model. First, in the weak field limit, the small-scale turbulent dynamo leads to a significantly increased flux in the core and we find |R| ~< 1. Second, in the strong field limit, field reversals in the envelope also lead to values |R| ~< 1. These reversals are less likely to occur in the core region where the velocity field is more coherent and the internal velocity dispersion is typically subsonic.

12 pages, 8 figures, accepted for publication in MNRAS

References in corpus (14)

• Theory of Star Formation
• Cold Dark Clouds: The Initial Conditions for Star Formation
• A new Jeans resolution criterion for (M)HD simulations of self-gravitating gas: Application to magnetic field amplification by gravity-driven turbulence
• Mach Number Dependence of Turbulent Magnetic Field Amplification: Solenoidal versus Compressive Flows
• The Nature of the Dense Core Population in the Pipe Nebula: Thermal Cores Under Pressure
• Numerical simulations of compressively driven interstellar turbulence: I. Isothermal gas
• From the warm magnetized atomic medium to molecular clouds
• The Fractal Density Structure in Supersonic Isothermal Turbulence: Solenoidal versus Compressive Energy Injection
• The generation of strong magnetic fields during the formation of the first stars
• A robust numerical scheme for highly compressible magnetohydrodynamics: Nonlinear stability, implementation and tests
• Molecular Cloud Evolution IV: Magnetic Fields, Ambipolar Diffusion, and the Star Formation Efficiency
• The Perils of Clumpfind: The Mass Spectrum of Sub-structures in Molecular Clouds
• The structure of molecular clouds and the universality of the clump mass function
• Self-Consistent Analysis of OH-Zeeman Observations: Too Much Noise about Noise

Cited by in corpus (9)

• The Star Formation Rate of Turbulent Magnetized Clouds: Comparing Theory, Simulations, and Observations
• Inefficient star formation through turbulence, magnetic fields and feedback
• Self-similar Fragmentation Regulated by Magnetic Fields in a Massive Star Forming Filament
• Magnetized Interstellar Molecular Clouds. I. Comparison Between Simulations and Zeeman Observations
• Accretion and magnetic field morphology around Class 0 stage protostellar discs
• Magnetized converging flows towards the hot core in the intermediate/high-mass star-forming region NGC 6334 V
• Simulations of the star-forming molecular gas in an interacting M51-like galaxy: cloud population statistics
• The Link between Magnetic-field Orientations and Star Formation Rates
• The sub-critical illusion: synthetic Zeeman effect observations from galactic zoom-in simulations