Ambipolar Diffusion in Action: Transient C shock Structure and Prestellar Core Formation

Abstract

We analyze the properties of steady and time-dependent C shocks under conditions prevailing in giant molecular clouds. For steady C shocks, we show that ionization equilibrium holds and use numerical integrations to obtain the shock thickness mediated by ambipolar diffusion as a function of density, inflow velocity, magnetic field, and ionization fraction in the cloud. Our formula also agrees with an analytic estimate based on ion-neutral momentum exchange. Using time-dependent numerical simulations, we show that C shocks have a transient stage when the neutrals are compressed much more strongly than the magnetic field. The transient stage has a duration set by the neutral-ion collision time, t_AD ~ L_shock/v_drift ~ 0.1 - 1 Myr. This transient creates a strong enhancement in the mass-to-magnetic flux ratio. Under favorable conditions, supercritical prestellar cores may form and collapse promptly as a result of magnetic flux loss during the transient stage of C shocks.

44 pages, 11 figures, 2 table, accepted for publication in Astrophysical Journal

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Cited by in corpus (19)

• Formation of Magnetized Prestellar Cores with Ambipolar Diffusion and Turbulence
• Change of Magnetic Field$-$Gas Alignment at Gravity-Driven Alfvénic Transition in Molecular Clouds: Implications for Dust Polarization Observations
• Anisotropic Formation of Magnetized Cores in Turbulent Clouds
• Prestellar Core Formation, Evolution, and Accretion from Gravitational Fragmentation in Turbulent Converging Flows
• Geometry, Kinematics, and Magnetization of Simulated Prestellar Cores
• A New Method to Trace Three-dimensional Magnetic Field Structure within Molecular Clouds Using Dust Polarization
• The Responses of Magnetically Sub-Critical Cores to Shocks
• Connecting the Scales: Large Area High-resolution Ammonia Mapping of NGC 1333
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• GMC Collisions As Triggers of Star Formation. IV. The Role of Ambipolar Diffusion
• Magnetic Fields and Star Formation
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