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Title: The role of large scale flows in molecular cloud formation in spiral galaxies
Author: Ramon Fox, Felipe Gerardo
ISNI:       0000 0004 7963 1744
Awarding Body: University of St Andrews
Current Institution: University of St Andrews
Date of Award: 2019
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Star formation begins on the large scales of a galaxy and takes place on the smallest scales. As the interstellar gas flows into a spiral arm, it forms a shock where the change in density, coupled to self-gravity and thermal instabilities, leads to the formation of high density structures where molecular clouds grow. It is important to understand the role of large-scale flows in assembling these clouds. This work explores the gas flows in spiral arms to understand its role on molecular cloud formation comparing between grand-design and flocculent galaxies. A set of high-resolution smoothed particle hydrodynamics (SPH) simulations are used. One simulation evolves the gas in a potential including a halo, stellar disc, and spiral arms. The second simulation evolves the gas in an N-body stellar disc and bulge within a fixed halo potential. The first and second models are representative of grand-design and flocculent galaxies, respectively. The third simulation is a high-resolution simulation of a region of gas flowing in a spiral arm based on the simulations of Bonnell et al. (2013), which follows in more detail the local cloud dynamics. In the global models, the mass resolution is about 45M⊙ per gas particle and in the spiral simulation, about 0.6M⊙. The results show that in both the grand-design and flocculent models, the gas is shocked as it flows through an arm. The N-body model shows flow characteristics qualitatively similar to the spiral potential model but with more variations due to the potentials arm-to-arm variations. Clouds are identified using a friends-of-friends algorithm to catalogue clumps above a given density threshold. These have non-negligible streaming motions and their properties are consistent with observed mass-radius and size-velocity dispersion relations.
Supervisor: Bonnell, Ian Alexander Sponsor: European Research Council (ERC) ; University of St Andrews
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
Keywords: Hydrodynamics ; Interstellar medium--Kinematics and dynamics ; Interstellar medium--Molecular clouds--Formation ; Galaxies--Kinematics and dynamics ; Milky Way--Structure ; Astrophysics--Astrophysics of galaxies