On the probability density function of galactic gas. I. numerical simulations and the significance of the polytropic index

摘要

We investigate the from the one-point probability density function (pdf) for the density field of the interstellar medium using numerical simulations that successively reduce the number of physical pro- cesses included. Two-dimensional simulations of self-gravitating supersonic MHD turbulence, of super- sonic self-gravitating hydrodynamic turbulence, and of decaying Burgers turbulence produce in all cases filamentary density structures and evidence for a power-law density pdf at large densities with logarith- mic slope between -1.7 and -2.3. This suggests that a power-law shape of the pdf and the general filamentary morphology are the signature of the nonlinear advection operator.