Dynamical Evolution of the Turbulent Interstellar Medium at the Kiloparsec Scale

Abstract

The interstellar medium (ISM) is a highly compressible medium, with pervasive magnetic fields, abundant energy sources such as supernova blasts, expanding HII regions, bipolar outflows, large-scale shear due to differential rotation, etc., and a range of densities spanning at least nine orders of magnitude (see e.g. [1]), from the rare, hot diffuse medium with n ~ 10⁻³ cm⁻³ to the densest clumps in molecular clouds with now n ~ 10⁶ cm⁻³. Thus a better understanding of turbulent motions within the interstellar medium is in demand. For example, shocks have been known for a long time to play an essential role in star and cloud formation, be it the density wave at the origin of the spiral structure of the galaxy, or the blast wave emanating from a supernova. Many approaches can be found in the literature (e.g. [2] [3] [4]) to tackle this problem. This paper is devoted to the description of the model developed in this context at the kiloparsec scale [5] [6] [7]. It incorporates magnetic fields, heating and cooling, self-gravity, thresholded and discrete star formation, rotation and shear; numerical computations using a pseudo-spectral code and hyper-viscosities have been performed, mostly in two dimensions; some of their results are described succinctly here.