Turbulent Diffuse Molecular Media with Non-ideal Magnetohydrodynamics and Consistent Thermochemistry: Numerical Simulations and Dynamic Characteristics

TL;DR

This study uses advanced 3D simulations to explore the complex interplay of turbulence, chemistry, and magnetic fields in diffuse molecular clouds, revealing significant chemical and thermal variability influenced by physical parameters.

Contribution

It introduces detailed non-ideal MHD simulations with time-dependent thermochemistry, highlighting the impact of magnetic fields and turbulence on cloud properties, which advances understanding of diffuse molecular media.

Findings

Chemical abundances vary by over an order of magnitude during early evolution.

Strong magnetic fields suppress gas compression and reduce warm gas fractions.

Chemical and thermal distributions are significantly affected by turbulence and magnetic effects.

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 non-equilibrium thermochemistry co-evolved 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 ($t\lesssim 2\times 10^5~{\rm yr}$). Various simulations are also conducted to study the impacts of physical parameters. Non-ideal MHD effects are essential in shaping the behavior of gases, and strong magnetic fields ($\sim 10~\mu{\rm G}$) tend to inhibit vigorous compressions and thus reduce the fraction of warm gases ($T\gtrsim 10^2~{\rm K}$). 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.