The Interaction of Astrophysical Flows with Clouds and Filaments

This thesis presents numerical simulations of the interaction of winds and shocks with clouds and filaments. Firstly, the shock-driven evolution of a 3D filament in a magnetised medium is investigated by varying the shock Mach number, cloud density contrast (χ), magnetic field strength and orientation, and cloud aspect ratio and angle to the shock. The morphology and lifetime of the filament is compared between simulations and the conditions that best extend the lifetime of the filament (e.g. a mild shock and a perpendicular/oblique magnetic field) are noted. The orientation of the magnetic field has a significant effect on the lifetime of the filament. Moreover, filaments in a parallel magnetic field can survive for longer if they are orientated ‘broadside’ to the shock front.
Secondly, a comparison of shock-cloud and wind-cloud interactions with increas- ing wind Mach number at both low and high χ is presented. This is the first study to demonstrate Mach scaling in a wind-cloud study and differences between wind-cloud and shock-cloud simulations at low χ. It also notes the shorter normalised cloud mixing time for the wind case, as well as the lack of Mach number dependence for that time-scale and the normalised cloud drag time at higher χ. Additionally, there are significant morphological differences between the two processes, particularly in the progress of the shock through the cloud and in the formation of tails in the higher χ simulations.
Finally, previous shock-filament studies are extended into the isothermal regime. The most significant finding is the large variation in the normalised evolution of the filament at high Mach numbers. Furthermore, the ‘three-rolled’ structure observed in previous adiabatic studies is present only in sideways-oriented filaments with χ = 100.