Astronomy and Astrophysics – Astrophysics
Scientific paper
1998-10-20
Astronomy and Astrophysics
Astrophysics
34 pages, 7 postscript figures, to appear in ApJ 3/1/99
Scientific paper
10.1086/306842
The molecular component of the Galaxy is comprised of turbulent, magnetized clouds, many of which are self-gravitating and form stars. To understand how these clouds' evolution may depend on their level of turbulence, mean magnetization, and degree of self-gravity, we perform a survey of direct numerical MHD simulations in 2.5 dimensions. Two of our independent survey parameters allow us to model clouds which either meet or fail conditions for magneto-Jeans stability and magnetic criticality. Our third survey parameter allows us to initiate turbulence of either sub- or super-Alfv\'enic amplitude. We evaluate the times for each cloud model to become gravitationally bound, and measure each model's kinetic energy loss over the fluid flow crossing time. We compare the evolution of density and magnetic field structural morphology, and quantify the differences in the density contrast generated by internal stresses, for models of differing mean magnetization. We find that the values of (c_s/v_A)^2 and L/L_Jeans, but not the initial Mach number v/c_s, determine the time for cloud gravitational binding and collapse. We find, contrary to some previous expectations, less than a factor of two difference between turbulent decay times for models with varying magnetic field strength. In all models, we find turbulent amplification in the magnetic field strength, with the turbulent magnetic energy between 25-60% of the turbulent kinetic energy after one flow crossing time. We find that for non-self-gravitating stages of evolution, the mass-averaged density contrast magnitudes
Gammie Charles F.
Ostriker Eve C.
Stone James M.
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