Chemodynamics in Star-Forming Molecular Clouds

Licentiate thesis, 2021

Stars are fundamental building blocks of galaxies. However, the answers to many basic questions about their formation remain elusive. There is no consensus on a theory that can predict the rate of star formation, its clustering properties, and the conditions needed for massive stars to be born. Although stars are known to form from dense regions of molecular clouds, measuring the physical properties in such regions is an outstanding challenge. Astrochemistry is the crucial set of processes that control the chemical evolution of the universe. It is important for controlling physical evolution, e.g., by setting heating and cooling rates and ionization fractions, but also for allowing predictions to be made for the emission from key diagnostic species to probe interstellar processes, such as star formation. To reconstruct the three-dimensional structures of galaxies and their interstellar media, chemodynamics, which is the combination of hydrodynamics and chemistry, is necessary.

In this thesis, chemodynamical simulations are applied to star-forming regions to follow their combined physical and chemical evolution and make predictions for observations. In particular a gas phase deuterium fractionation network is applied to massive prestellar core simulations. Various chemical model parameters are investigated to understand whether fast collapse of a turbulent, magnetised prestellar core can achieve the high levels of deuteration that are commonly observed in such systems. The structure, kinematics and dynamics of the core, as traced by the rotational transitions of the key diagnostic species of $\rm N_2D^+$, are investigated. Another astrochemical network, including gas-grain processes, is constructed for simulations of larger-scale, generally lower density molecular clouds and applied to a simulation of giant molecular cloud collisions. We also discuss the computational performance of our chemodynamical simulations and summarize some methods to improve their efficiency.