The effects of gravitation and fluid dynamics on velocity estimation by stagnation point method of a minor galaxy cluster merger, by analysis of full hydro + N-body simulations

Fish, Thomas Marrick

Abstract

Galaxy clusters are collections of galaxies that grow by merging with galaxies or other clusters. Galaxy clusters are predominantly dark matter and a hot plasma called the intracluster medium (ICM), which can be observed through X-ray bright emission. Using X-ray observations of this fluid plasma, the stagnation point method (SPM) can be applied to estimate the velocity of a galaxy or subcluster merging with its host cluster. However, the efficacy of this cannot be tested in the real world due to the timescales over which mergers occur, so this thesis presents a careful analysis of a series of hydrodynamic + N-body simulations of the Fornax cluster to assess the applicability of several versions of the SPM. This analysis was applied throughout the simulations to cover a range of scenarios from a typical minor merger. A new modification to the SPM was also tested, which additionally considers the effects of gravity on the surrounding ICM. This modification improved the accuracy of the SPM during the first infall of each simulation, whereas the other methods significantly overestimated the velocity during this period. Following this, from pericentre passage until after apocentre passage, the SPM was found to be unsuitable as the flow could not be considered stable. During later infalls, the disturbed ICM made the definition of the free stream variables unreliable, which caused systematic issues and highlights the difficulties in defining free stream variables, even within a simplified, but realistic, scenario. This thesis sets out a range of recommendations to help assess validity and improve the application of the SPM to minor mergers. We also recommend the use of the new SPM that includes gravity, with careful modelling of the gravitational potential.

Citation

Fish, T. M. (2020). The effects of gravitation and fluid dynamics on velocity estimation by stagnation point method of a minor galaxy cluster merger, by analysis of full hydro + N-body simulations. (Thesis). University of Hull. Retrieved from https://hull-repository.worktribe.com/output/4224503

• Thesis Type: Thesis
• Deposit Date: Dec 6, 2022
• Publicly Available Date: Feb 24, 2023
• Keywords: Physics
• Public URL: https://hull-repository.worktribe.com/output/4224503
• Additional Information: Department of Physics and Mathematics, The University of Hull
• Award Date: Jun 1, 2020