Projected velocity statistics of interstellar turbulence

TL;DR

This paper introduces a new method to analyze interstellar turbulence by using projected velocity structure functions, enabling the study of turbulence spectra, cloud thickness, and driving scales from observational data.

Contribution

It presents a novel approach to extract turbulence statistics from projected velocity data, applicable across different interstellar phases and turbulence regimes.

Findings

Identified a transition from Kolmogorov to Burgers turbulence scaling in Taurus cloud.

Demonstrated the method's ability to determine cloud thickness and turbulence driving scale.

Revealed that small-scale compressive motions occupy a minor volume fraction.

Abstract

Velocity statistics is a direct probe of the dynamics of interstellar turbulence. Its observational measurements are very challenging due to the convolution between density and velocity and projection effects. We introduce the projected velocity structure function, which can be generally applied to statistical studies of both sub- and super-sonic turbulence in different interstellar phases. It recovers the turbulent velocity spectrum from the projected velocity field in different regimes, and when the thickness of a cloud is less than the driving scale of turbulence, it can also be used to determine the cloud thickness and the turbulence driving scale. By applying it to the existing core velocity dispersion measurements of the Taurus cloud, we find a transition from the Kolmogorov to the Burgers scaling of turbulent velocities with decreasing length scales, corresponding to the large-scale solenoidal motions and small-scale compressive motions, respectively. The latter occupy a small fraction of the volume and can be selectively sampled by clusters of cores with the typical cluster size indicated by the transition scale.