Morphology, fragmentation, and dynamic balance: an investigation into early stages of structure formation in molecular clouds

How molecular clouds fragment and create the dense structures which go on to eventually form stars is an open question. This thesis numerically investigates vari- ous aspects of fragmentation and structure formation in young molecular clouds based on the SILCC-Zoom and SILCC deep-zoom simulations. The SILCC-Zoom simulations follow the self-consistent formation of molecular clouds in a few hun- dred parsec sized region of a stratified galactic disc, which include (self-) gravity, magnetic fields, supernova driven turbulence, as well as a non-equilibrium chem- ical network and treatment of the interstellar radiation field, with resolutions of ∼ 0.1 parsec. The SILCC deep-zoom simulations are an extension of the cloud scale SILCC-Zoom simulations and allow us to resolve structures with a maximum res- olution of 0.0078 parsec ( ∼ 1600 AU). We identify 3D volumes inside the simulated clouds as structures using dendrograms and analyze their behaviour. By consider- ing the energetic balance of cloud scale sub-structures, we find that our molecular clouds are dominated by the interplay of turbulence and self-gravity - with self- gravity becoming dynamically dominant only over time. This supports the gravo- turbulent scenario of structure formation. By tracing the morphology of cloud scale structures, we evaluate our clouds to be sheet-like on larger scales, likely tracing the shells of bubbles driven by supernovae. We estimate the effect of magnetic fields in molecular clouds and their atomic envelopes and find that magnetic fields alter the nature of fragmentation at low densities, slow down the formation of denser structures, but do not seem to be dynamically important in the further evolution of these potentially star forming sub-structures. We extend the study of energet- ics and morphology to sub-pc scale structures using the novel SILCC deep-zoom simulations. We find different methods of forming filaments - fragmentation of mostly self-gravitating structures, as well as shock compression. Moreover, we find that gravitationally bound, spheroidal cores emerge at ∼ 0.1 parsec scales and are embedded inside gravitationally dominated filaments