MOLECULAR TRACERS OF TURBULENT SHOCKS IN GIANT MOLECULAR CLOUDS

2012/01/25 by A. Pon, Andy Pon, Doug Johnstone +3
Physics and Astronomy · #Ambipolar diffusion #Astrophysics #Astrophysics and Star Formation Studies #Atomic physics #Computational physics #Dissipation #Galaxies: Formation, Evolution, Phenomena #Magnetohydrodynamic turbulence #Magnetohydrodynamics #Mechanics #Molecular cloud #Nuclear physics #Optics #Physics #Plasma #Radiative cooling #Radiative transfer #Shock (circulatory) #Shock wave #Stellar, planetary, and galactic studies #Supersonic speed #Thermodynamics #Turbulence #astro-ph.GA

paper · pdf · doi:10.1088/0004-637x/748/1/25

published as ApJ 748 (2012) 25-39 · 14 pages, 5 figures, accepted for publication in ApJ; minor grammatical errors corrected

arxiv created 2012/01/25 · openalex publication_date 2012/03/01 · arxiv updated 2012/07/13 · openalex created_date 2025/10/10 · openalex updated_date 2026/08/05

Abstract

Giant molecular clouds contain supersonic turbulence and simulations of magnetohydrodynamic 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 −1 , 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.

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