Turbulent Diffuse Molecular Media with Nonideal Magnetohydrodynamics and Consistent Thermochemistry: Numerical Simulations and Dynamic Characteristics

Abstract

Turbulent diffuse molecular clouds can exhibit complicated morphologies caused by the interactions among radiation, chemistry, fluids, and fields. We performed full 3D simulations for turbulent diffuse molecular interstellar media, featuring time-dependent nonequilibrium thermochemistry coevolved with magnetohydrodynamics (MHD). Simulation results exhibit the relative abundances of key chemical species (e.g., C, CO, OH) vary by more than one order of magnitude for the “premature” epoch of chemical evolution ( t ≲ 2 × 10 ^5 yr). Various simulations are also conducted to study the impacts of physical parameters. Nonideal MHD effects are essential in shaping the behavior of gases, and strong magnetic fields (∼10 μ G) tend to inhibit vigorous compressions and thus reduce the fraction of warm gases ( T ≳ 10 ^2 K). Thermodynamical and chemical conditions of the gas are sensitive to modulation by dynamic conditions, especially the energy injection by turbulence. Chemical features, including ionization (cosmic ray and diffuse interstellar radiation), would not directly affect the turbulence power spectra. Nonetheless, their effects are prominent in the distribution profiles of temperatures and gas densities. Comprehensive observations are necessary and useful to eliminate the degeneracies of physical parameters and constrain the properties of diffuse molecular clouds with confidence.

Keywords

• Interstellar medium
• Molecular clouds
• Astrochemistry
• Hydrodynamical simulations
• Magnetohydrodynamical simulations