Wednesday 10 Dec 2014: Seminar: Filament formation in MHD turbulence
Dr Eva Ntormousi - CEA, Saclay (Paris)
Physics, 4th floor 14:00-15:00
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. From a theoretical point of view, explaining the properties of these filaments will point to the physical mechanisms regulating the Galactic ISM. To that end, in this work we employ high-resolution, 3D MHD simulations performed with the AMR code RAMSES to investigate different filament formation mechanisms. The first series of simulations has the particular aim to address the origin of the characteristic filament thickness found in observations.
Starting from the hypothesis that diffusive processes are responsible, our numerical experiments consist of (driven or decaying) ideal and non-ideal MHD turbulence, at a resolution that greatly exceeds the reported 0.1pc thickness. The comparison points to ion-neutral friction as an excellent candidate for setting a characteristic scale. In this picture dense filaments are the diffusive end of the turbulent cascade, an interpretation with important implications for our understanding of the dynamical behavior of the ISM.
A second series of simulations investigates filament formation by the fragmentation of large-scale shocks. We find a striking difference between hydrodynamical and MHD runs as in the first case the sheets fragment into small cores, while in the latter they produce large filaments. In addition though, we see that low-density filaments preferentially form along the dominant component of the magnetic field. In this scenario filaments are prominent features in the ISM, but their fate is still determined by the local magnetic field.
A detailed comparison of the filament properties between the two runs is work in progress and will reveal the physical mechanisms responsible for shaping the ISM and setting the initial conditions for star formation.