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"Formation of interstellar filaments: the role of magnetic fields"
Dr. Eva Ntormousi, CEA/Saclay, France
CEA/Saclay, France

When:  Thursday 21 August 2007 at 1:00pm
Where: 2nd Floor Seminar Room

Abstract:

The filamentary structure of interstellar matter and its potential link to star formation has been brought back into focus recently by high resolution observational surveys, such as Herschel. Among the plethora of interesting results, an especially puzzling matter is that local interstellar filaments appear to have a preferred thickness of 0.1 pc, which is independent of their column density. We present a theory which views filaments as the diffusive end of the interstellar turbulence cascade, so that diffusive processes such as ambipolar diffusion are setting this characteristic thickness. For this we employ high-resolution, 3D MHD simulations with the AMR code RAMSES   to investigate non-ideal MHD turbulence as a filament formation mechanisms.  The main focus of this analysis is the thickness distribution of the resulting structures.  

Simulations of both driven and decaying MHD turbulence show a different morphology when ambipolar diffusion is included in the model.  In particular, dense structures appear broader due to ion-neutral friction.  The magnitude of this effect, however, depends on the chosen threshold for identifying filaments. Although the peak in the thickness distribution of filaments is not as dramatic in this series of simulations as in the observations, the comparison between ideal and non-ideal MHD simulations shows that ambipolar diffusion does alter the morphology of MHD turbulence and especially affects the thickness distribution of the structures.

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