Atomic chemistry in turbulent astrophysical media. I. EFFECT OF Atomic cooling

We carry out direct numerical simulations of turbulent astrophysical media that explicitly track ionizations, recombinations, and species-by-species radiative cooling. The simulations assume solar composition and follows the evolution of hydrogen, helium, carbon, oxygen, sodium, and magnesium, but they do not include the presence of an ionizing background. In this case, the medium reaches a global steady state that is purely a function of the one-dimensional turbulent velocity dispersion, σ_1D, and the product of the mean density and the driving scale of turbulence, nL. Our simulations span a grid of models with ${\sigma }_{1D}$ ranging from 6 to 58 km s⁻¹ and nL ranging from 10¹⁶ to 10²⁰ cm⁻², which correspond to turbulent Mach numbers from M = 0.2 to 10.6. The species abundances are well described by single-temperature estimates whenever M is small, but local equilibrium models can not accurately predict the global equilibrium abundances when $M\gtrsim 1.$ To allow future studies to account for nonequilibrium effects in turbulent media, we gather our results into a series of tables, which we will extend in the future to encompass a wider range of elements, compositions, and ionizing processes.