Spectral Properties of Interstellar Turbulence via Velocity Channel Analysis

Abstract

In this presentation we review the link between the statistics of intensity fluctuations in spectral line data cubes with underlying statistical properties of turbulence in the interstellar medium. Both the formalism of Velocity Channel Analysis for optically thin lines and its extension to the lines with self-absorption is described. We demonstrate that by observing optically thin lines from cold gas in sufficiently narrow (thin) velocity channels one may recover the scaling of the stochastic velocities from turbulent cascade, in particular, Kolmogorov velocities give $K^{-2.7}$ contribution to the intensity power spectrum. Synthetically increasing the channel thickness separates out the underlying density inhomogeneities of the gas. Effects of self absorption, on the other hand, retain the velocity signature even for integrated lines. As a result, intensity fluctuations tend to show universal but featureless scaling of the power $\propto K^{-3}$ over the range of scales.