Cloud/Intercloud Structure from Nonlinear Magnetic Waves
B. G. Elmegreen;
ApJ, 1997, 480, 674
ABSTRACT:One-dimensional numerical simulations of interacting plane-polarized Alfven waves including magnetic diffusion and thermal energy
dissipation form structures between the sources of excitation that are analogous
to clumpy cool diffuse clouds surrounded by a warm low-density
intercloud medium.
The cloud oscillates slightly after formation but has an
average state that is in both thermal and total pressure equilibrium with the
intercloud medium.
The cloud substructure has a realistic size--line width
relation, Delta v ~ R0.5, that is the result of a systematically decreasing
correlation among random motions for increasingly large scales.
The
substructure also has a peak-density versus size relation rho ~ R-0.18 because of
self-similar hierarchical structure.
The gas continuously changes its
temperature in response to density fluctuations in the turbulent medium, i.e.,
each region picks the temperature of the nearest equilibrium phase for the
current density.
The gas motions are generally less than the Alfven speed and
comparable to the sound speed.
This implies that supersonic turbulence in real
clouds is probably the result of supersonic relative motions between very
tiny clumps inside which the actual motions are nearly sonic.
The magnetic
field plays the important role of allowing energy from the perturbation to
spread over a large distance with minimal dissipation.
KEYWORDS: ism: clouds, ism: kinematics and dynamics, ism: magnetic fields, polarization, waves
PERSOKEY:magnetic field, statistical analysis, simulation, ,
CODE: elmegreen97a