MHD simulation of the formation of clumps and filaments in quiescent diffuse medium by thermal instability

Abstract

We have used the AMR hydrodynamic code, MG, to perform idealised 3D MHD simulations of the formation of clumpy and filamentary structure in a thermally unstable medium without turbulence. A stationary thermally unstable spherical diffuse atomic cloud with uniform density in pressure equilibrium with low density surroundings was seeded with random density variations and allowed to evolve. A range of magnetic field strengths threading the cloud have been explored, from beta=0.1 to beta=1.0 to the zero magnetic field case (beta=infinity), where beta is the ratio of thermal pressure to magnetic pressure. Once the density inhomogeneities had developed to the point where gravity started to become important, self-gravity was introduced to the simulation. With no magnetic field, clouds and clumps form within the cloud with aspect ratios of around unity, whereas in the presence of a relatively strong field (beta=0.1) these become filaments, then evolve into interconnected corrugated sheets that are predominantly perpendicular to the magnetic field. With magnetic and thermal pressure equality (beta=1.0), filaments, clouds and clumps are formed. At any particular instant, the projection of the 3D structure onto a plane parallel to the magnetic field, i.e. a line of sight perpendicular to the magnetic field, resembles the appearance of filamentary molecular clouds. The filament densities, widths, velocity dispersions and temperatures resemble those observed in molecular clouds. In contrast, in the strong field case beta=0.1, projection of the 3D structure along a line of sight parallel to the magnetic field reveals a remarkably uniform structure.

17 pages, 10 figures. Accepted to MNRAS, minor changes and additions to text, primarily in Section 6

References in corpus (17)

• Cold Dark Clouds: The Initial Conditions for Star Formation
• Filamentary structure of star-forming complexes
• Molecular Cloud Evolution II. From cloud formation to the early stages of star formation in decaying conditions
• From the warm magnetized atomic medium to molecular clouds
• Magnetic Fields in High-Mass Infrared Dark Clouds
• Magnetically Regulated Star Formation in 3D: The Case of Taurus Molecular Cloud Complex
• On the nature of star-forming filaments: I. Filament morphologies
• Is Turbulence in the Interstellar Medium Driven by Feedback or Gravity? An Observational Test
• Strong Lens Time Delay Challenge: II. Results of TDC1
• The dynamical properties of dense filaments in the infrared dark cloud G035.39-00.33
• Aspect Ratio Dependence of the Free-Fall Time for Non-Spherical Symmetries
• SCUBA and Spitzer observations of the Taurus molecular cloud - pulling the bull's tail
• Core and filament formation in magnetized, self-gravitating isothermal layers
• The Role of Turbulence and Magnetic Fields in Simulated Filamentary Structure
• Feedback from Winds and Supernovae in Massive Stellar Clusters - II. X-Ray Emission
• Filament L1482 in the California molecular cloud
• A Dynamically Collapsing Core and a Precursor of a Core in a Filament Supported by Turbulent and Magnetic Pressures

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