Description of turbulent dynamics in the interstellar medium: Multifractal-microcanonical analysis I. Application to Herschel observations of the Musca filament

Vol. 649
6. Interstellar and circumstellar matter

Description of turbulent dynamics in the interstellar medium: Multifractal-microcanonical analysis I. Application to Herschel observations of the Musca filament

by H. Yahia, N. Schneider, S. Bontemps, et al. 2021, A&A, 649, A33 alt

The flow of energy in turbulence between the source and dissipation scales is a self-similar irreversible cascade process. For engineers this loss of energy from the system is a phenomenological nuisance since star formation is the core mystery: the impediment to collapse presented by the large-scale motions must be eliminated before the gas can become gravitationally dominated, but how does this dissipation occur? The signature of this process is non-Gaussianity, called “intermittency," which is the revelation of spatial and velocity correlations. This can be understood through the analysis of the singular points in the flow where the velocity gradients are steepest, hence regions of strong coupling. The authors provide a superb introduction to the multifractals and present new methods to reveal and analyze these structures in far-infrared molecular cloud images with Herschel. Here the focus is on the Musca filament as a demonstration, comparing their results with magnetohydrodynamic (MHD) simulations and demonstrating the presence of a cascade over an order of magnitude in length with a driving at parsec scales with intermittency operating in a spectacular array of small-scale filaments and knots.