A. Pon, D. Johnstone, M. J. Kaufman
Giant molecular clouds contain supersonic turbulence and simulations of MHD
turbulence show that these supersonic motions decay in roughly a crossing time,
which is less than the estimated lifetimes of molecular clouds. Such a
situation requires a significant release of energy. We run models of C-type
shocks propagating into gas with densities around 10^3 cm^(-3) at velocities of
a few km / s, appropriate for the ambient conditions inside of a molecular
cloud, to determine which species and transitions dominate the cooling and
radiative energy release associated with shock cooling of turbulent molecular
clouds. We find that these shocks dissipate their energy primarily through CO
rotational transitions and by compressing pre-existing magnetic fields. We
present model spectra for these shocks and by combining these models with
estimates for the rate of turbulent energy dissipation, we show that shock
emission should dominate over emission from unshocked gas for mid to high
rotational transitions (J >5) of CO. We also find that the turbulent energy
dissipation rate is roughly equivalent to the cosmic ray heating rate and that
the ambipolar diffusion heating rate may be significant, especially in shocked
gas.
View original:
http://arxiv.org/abs/1201.1919
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