Eva Ntormousi Colloquium: Formation and evolution of diffuse molecular filaments

The interstellar medium is threaded by a complex network of molecular filaments which range from low-density, relatively diffuse structures to dense, star-forming regions. The Gould Belt survey of the Herschel space observatory studied these filaments in great detail and found that they all have the same central thickness of 0.1 pc in submm dust continuum. A theoretical explanation for this property can provide an important insight into ISM physics.

I will present a theory in which the 0.1 pc thickness of these filaments represents the cut-off scale of the ISM turbulent cascade. In particular, we consider ion-neutral friction damping of Alfven waves responsible for this cut-off and we investigate this scenario with high resolution, 3D simulations of ideal and non-ideal MHD turbulence. The simulations are designed to resolve the ion-neutral friction scale with at least 25 grid cells.

When ambipolar diffusion is included, both driven and decaying turbulence experiments show a significant change in the number of filaments formed and in their appearance. Although the dynamical range of the simulations is still not enough for an exact comparison to observations, this work shows that non-ideal MHD effects are essential in the study of ISM turbulence and that ambipolar diffusion in particular is a very good candidate for setting the characteristic 0.1 pc scale of molecular filaments.

A plot is attached, showing column densities in two turbulence simulations: ideal and non-ideal MHD.