Emissivity Statistics in Turbulent Compressible Magnetohydrodynamic Flows and the Density-Velocity Correlation
A. Lazarian, D. Pogosyan, E. V\'azquez-Semadeni, B. Pichardo;
ApJ, 2001, 555, 130
ABSTRACT:In this paper we test the results of a recent analytical study by Lazarian and Pogosyan on the statistics of emissivity in velocity channel maps,
in the case of realistic density and velocity fields obtained from
numerical simulations of magnetohydrodynamic turbulence in the interstellar
medium.
To compensate for the lack of well-developed inertial ranges in the
simulations owing to the limited resolution, we apply a procedure for modifying the
spectral slopes of the fields while still preserving the spatial
structures.
We find that the density and velocity are moderately correlated in space,
and we prove that the analytical results by Lazarian and Pogosyan hold in
the case when these fields obey the fluid conservation equations.
Our
results imply that the spectra of velocity and density can be safely recovered
from the position-position-velocity (PPV) data cubes available through
observations and confirm that the relative contributions of the velocity and
density fluctuations to those of the emissivity depend on the velocity
resolution used and on the steepness of the density spectral index.
Furthermore,
this paper supports previous reports that an interpretation of the
features in the PPV data cubes as simple density enhancements (i.e.,
``clouds'') can often be erroneous, as we observe that changes in the velocity
statistics substantially modify the emissivity statistics within the velocity
data cubes.
KEYWORDS: ism: general, ism: structure, radio lines: ism, turbulence
PERSOKEY:turbulence, ,
CODE: lazarian2001