Interstellar Turbulence. II. Energy Spectra of Molecular Regions in the Outer Galaxy
C. M. Brunt, M. H. Heyer;
ApJ, 2002, 566, 289
ABSTRACT:The multivariate tool of principal component analysis (PCA) is applied to
23 fields in the FCRAO CO Survey of the Outer Galaxy.
PCA enables the
identification of line profile differences, which are assumed to be generated from
fluctuations within a turbulent velocity field.
The variation of these velocity
differences with spatial scale within a molecular region is described by a singular
power law, δv=cLα, which can be used as a powerful
diagnostic to turbulent motions.
For the ensemble of 23 fields, we find a mean
value <α>=0.62+/-0.11.
From a recent calibration of this method
using fractal Brownian motion simulations (Brunt & Heyer), the
measured velocity difference-size relationship corresponds to an energy
spectrum, E(k), which varies as k-β, where
β=2.17+/-0.31.
We compare our results to both decaying and forced hydrodynamic
simulations of turbulence.
We conclude that energy must be continually injected
into the regions to replenish that lost by dissipative processes such as
shocks.
The absence of large, widely distributed shocks within the targeted
fields suggests that the energy is injected at spatial scales less than
several parsecs.
KEYWORDS: hydrodynamics, ism: clouds, ism: kinematics and dynamics, line: profiles, methods: statistical, turbulence
PERSOKEY:turbulence, ,
CODE: brunt2002