The Astrochemical Evolution of Turbulent Giant Molecular Clouds : I - Physical Processes and Method of Solution for Hydrodynamic, Embedded Starless Clouds

Abstract

Contemporary galactic star formation occurs predominantly within gravitationally unstable, cold, dense molecular gas within supersonic, turbulent, magnetized giant molecular clouds (GMCs). Significantly, because the chemical evolution timescale and the turbulent eddy-turnover timescale are comparable at typical GMC conditions, molecules evolve via inherently non-equilibrium chemistry which is strongly coupled to the dynamical evolution of the cloud. Current numerical simulation techniques, which include at most three decades in length scale, can just begin to bridge the divide between the global dynamical time of supersonic turbulent GMCs, and the thermal and chemical evolution within the thin post-shock cooling layers of their background turbulence. We address this GMC astrochemical scales problem using a solution methodology, which permits both complex three-dimensional turbulent dynamics as well as accurate treatment of non-equilibrium post-shock thermodynamics and chemistry. We present the current methodology in the context of the larger scope of physical processes important in understanding the chemical evolution of GMCs, including gas-phase chemistry, dust grains and surface chemistry, and turbulent heating. We present results of a new Lagrangian verification test for supersonic turbulence. We characterize the evolution of these species according to the dimensionless local post-shock Damköhler number, which quantifies the ratio of the dynamical time in the post-shock cooling flow to the chemical reaction time of a given species. Lastly, we discuss implications of this work to the selection of GMC molecular tracers, and the zeroing of chemical clocks of GMC cores.

arXiv comment35 pages, 7 figures, 16 tables. Accepted to MNRAS. Revised to correct some typographic errors

References in corpus (34)

• Theory of Star Formation
• Control of star formation by supersonic turbulence
• Interstellar Turbulence I: Observations and Processes
• Cold Dark Clouds: The Initial Conditions for Star Formation
• Comparing the statistics of interstellar turbulence in simulations and observations: Solenoidal versus compressive turbulence forcing
• The Statistics of Supersonic Isothermal Turbulence
• The Universality of the Stellar IMF
• The Energy Dissipation Rate of Supersonic, Magnetohydrodynamic Turbulence in Molecular Clouds
• The Density Probability Distribution in Compressible Isothermal Turbulence: Solenoidal versus Compressive Forcing
• Kinetic Energy Decay Rates of Supersonic and Super-Alfvenic Turbulence in Star-Forming Clouds
• Density probability distribution in one-dimensional polytropic gas dynamics
• Polycylcic Aromatic Hydrocarbons (PAH's) in dense cloud chemistry
• Simulating the formation of molecular clouds. I. Slow formation by gravitational collapse from static initial conditions
• Extensible Component Based Architecture for FLASH, A Massively Parallel, Multiphysics Simulation Code
• Simulating the formation of molecular clouds. II. Rapid formation from turbulent initial conditions
• Molecular Evolution and Star Formation: From Prestellar Cores to Protostellar Cores
• Numerical simulations of compressively driven interstellar turbulence: I. Isothermal gas
• Molecular Evolution in Collapsing Prestellar Cores III: Contraction of A Bonnor-Ebert Sphere
• Universal intermittent properties of particle trajectories in highly turbulent flows
• The Post-Shock Chemical Lifetimes of Outflow Tracers and a Possible New Mechanism to Produce Water Ice Mantles
• Models of turbulent dissipation regions in the diffuse interstellar medium
• Kolmogorov-Burgers Model for Star Forming Turbulence
• The Polytropic Equation of State of Interstellar Gas Clouds
• Algorithmic comparisons of decaying, isothermal, supersonic turbulence
• Intermittency and Universality in Fully-Developed Inviscid and Weakly-Compressible Turbulent Flows
• Density Probability Distribution Functions in Supersonic Hydrodynamic and MHD Turbulence
• The Temperature of Interstellar Clouds from Turbulent Heating
• Mixing in Supersonic Turbulence
• Adaptive Mesh Refinement for Supersonic Molecular Cloud Turbulence
• Statistical properties of supersonic turbulence in the Lagrangian and Eulerian frameworks
• The Kinematics of Molecular Cloud Cores in the Presence of Driven and Decaying Turbulence: Comparisons with Observations
• Ambipolar Drift Heating in Turbulent Molecular Clouds
• Hydrodynamical simulations of the decay of high-speed molecular turbulence. I. Dense molecular regions
• Hydrodynamical simulations of the decay of high-speed molecular turbulence. II. Divergence from isothermality

Cited by in corpus (5)

• KROME - a package to embed chemistry in astrophysical simulations
• Modeling the Atomic-to-Molecular Transition and Chemical Distributions of Turbulent Star-Forming Clouds
• SHOCKFIND - An algorithm to identify magnetohydrodynamic shock waves in turbulent clouds
• Neural networks: solving the chemistry of the interstellar medium
• Systematic selection of surrogate models for nonequilibrium chemistry