Star cluster formation involves the conversion of molecular gas into stars inside giant molecular clouds (GMCs). Such a process involves many dynamical evolution mechanisms, including mergers between smaller star clusters (subclusters) on which we focus in this thesis. We take results of simulations performed by Howard et al. 2018 (H18) which found that young massive cluster (YMC) formation is heavily dependant on the process of subcluster mergers, and we simulate said mergers at higher resolution. Subclusters inside such GMC simulations are modelled using the sink particle prescription which does not resolve individual star particles or gas parcels inside the subcluster they represent. We employ a more controlled method in simulating subcluster mergers to better understand the response of the stellar and gas components of a subcluster from the merger process. To do this, we take the parameters of the sink particles created in H18 and set up spheres of stars and gas. We use the AMUSE framework to couple the N-body evolution of the stars to the smoothed particle hydrodynamics (SPH) evolution of the gas such that both components of a given cluster can realistically react to each other. We model 15 of these mergers and find that once the velocity at which the two clusters collide (collisional velocity) exceeds $\approx 10$kms$^{-1}$, the resultant cluster is not monolithic (i.e. it still contains two separate stellar components) while all other simulations merge into one monolithic stellar and gas component cluster. We also find that, regardless of the collisional velocity of masses of the component clusters, all resultant clusters lose a fraction of their stellar and gas mass. This fraction is directly proportional to the collisional velocity and is a discrepancy between the sink particle prescription (where all mass is contained inside a constant sink particle accretion radius) and real cluster mergers. A further discrepancy we find is that all simulations result in a cluster whose outermost regions are expanding and that the rate of this expansion is somewhat proportional to the collisional velocity of the merger. These results point to the inaccuracy of the sink particle prescription and allow us to develop tools to improve on it in future simulations. Next, we fit commonly used analytical density profiles to both the stellar and gas component of our resultant clusters and find that, while they do not provide particularly excellent fits, they provide constraints on what is an acceptable fit. Lastly, we analyze the amount by which gas with potentially star forming densities increase due to the merger and we find that all mergers increase their star forming gas mass fraction by roughly 50 per cent implying that mergers may be an effective tool for triggering star formation.

Master of Science (MSc)

Thesis