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A numerical study of spiral galaxies and dynamical effects of spiral arms

Grand, RJJ; (2014) A numerical study of spiral galaxies and dynamical effects of spiral arms. Doctoral thesis , UCL (University College London). Green open access

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Abstract

We use high-resolution numerical simulations of disc galaxies to study spiral arms and their dynamical influence on nearby stars. We find that in the numerical simulations the spiral arms are winding, transient features whose pattern speeds decrease with radius in such a way that the pattern speed is almost equal to the rotation curve of the galaxy. We validate this for normal and barred-spirals, and demonstrate that there is no significant offset of different star-forming tracers across the spiral arm. We show from the dynamics of nearby star particles that star particles are drawn towards and join the spiral arm from behind (in front of) the arm and migrate towards the outer (inner) regions of the disc until the arm disappears. The resulting gain (loss) of angular momentum of star particles behind (in front of) the spiral arm is termed radial migration, and occurs over the entire radial range analyzed. A direct consequence of ubiquitous co-rotation radii is that the guiding centre radii of particles are changed while their degree of random motion is unchanged. We show that there are several types of migrator particles, as well as particles that do not migrate, that each have a different orbital evolution. We show that the orbital type depends on position in configuration and phase space, and show how the orbits can make up moving group features in velocity space. We investigate the correlation between the galactic shear rate and the pitch angle of both individual density waves and the apparent co-rotating spiral arms. We find that, in both cases, higher galactic shear rates produce more tightly wound spiral arms, in agreement with observation. We find also that winding spiral arms can naturally explain the scatter in the pitch angle-shear rate relation seen from observations.

Type: Thesis (Doctoral)
Title: A numerical study of spiral galaxies and dynamical effects of spiral arms
Open access status: An open access version is available from UCL Discovery
Language: English
UCL classification: UCL > Provost and Vice Provost Offices
UCL > Provost and Vice Provost Offices > UCL BEAMS
UCL > Provost and Vice Provost Offices > UCL BEAMS > Faculty of Maths and Physical Sciences
UCL > Provost and Vice Provost Offices > UCL BEAMS > Faculty of Maths and Physical Sciences > Dept of Space and Climate Physics
URI: https://discovery.ucl.ac.uk/id/eprint/1433765
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