Exponential Tails in the Centroid Velocity Distributions of Star-Forming Regions
M. S. Miesch, J. M. Scalo;
ApJ, 1995, 450, L27
ABSTRACT:Probability density functions (pdfs) of 13CO emission line centroid (line-of-sight, intensity-weighted average) velocities are presented for several
densely sampled molecular clouds as quantitative descriptors of their
underlying dynamics.
Some are found to be approximately Gaussian in form, but
most of the pdfs exhibit relatively broader, often nearly exponential,
tails, similar to the behavior found for pdfs of velocity differences and
derivatives (but not the velocity field itself) in experiments and numerical
simulations of incompressible turbulence.
Other nonturbulent processes can
also give rise to non-Gaussian pdfs, although we know of no interpretations
(turbulent or otherwise) that can unambiguously account for the nearly
exponential tails.
The centroid pdfs presented here are less sensitive to
systematic motions, optical depth effects, and secondary thermal components
than are individual molecular line profiles, which have also been used as
pdf estimators and which have also been recently found to exhibit excess
wing emission similar to the broad pdf tails found here.
KEYWORDS: ism: clouds, ism: molecules, stars: formation
PERSOKEY:turbulence, ,
CODE: miesch95