An observational method to measure the relative fractions of solenoidal and compressible modes in interstellar clouds

Abstract

We introduce a new method for observationally estimating the fraction of momentum density (ρv) power contained in solenoidal modes (for which ∇ · ρv = 0) in molecular clouds. The method is successfully tested with numerical simulations of supersonic turbulence that produce the full range of possible solenoidal/compressible fractions. At present, the method assumes statistical isotropy, and does not account for anisotropies caused by (e.g.) magnetic fields. We also introduce a framework for statistically describing density-velocity correlations in turbulent clouds. © 2014 The Authors. Published by Oxford University Press on behalf of the Royal Astronomical Society.