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Impact of cosmological satellite galaxies on the dynamics of the Milky Way disc

Moetazedian, Reza

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I present a high resolution study of the impact of realistic satellite galaxies, extracted from cosmological simulations of Milky Way-like haloes including 6 Aquarius and one Via Lactea II suites, on the dynamics of the Galactic disc. The initial conditions for the multi-component Milky Way galaxy were generated, to ensure an isolated system in a dynamical equilibrium state. After analysing the statistical properties of the subhaloes, candidates likely to impact the disc with the initial mass,tidal mass > 10^8 solar mass, were identified, inserted into our high resolution N-body simulations and evolved for 2 Gyr. I quantified the vertical heating due to such impacts by measuring the disc thickness and squared vertical velocity dispersion across the disc. According to our analysis, the strength of the heating is strongly dependent on the high mass end of the subhalo distribution from cosmological simulations. The mean increase of the vertical dispersion is approximately 20 km^2/s^2/Gyr for R > 4 kpc with a flat radial profile. Excluding Aq-F2 results with a very massive perturber with tidal mass = 6.10^10 solar mass, the mean heating is less than 12 km^^2/s^2/Gyr. These heating values correspond to 28% and 17% of the observed vertical heating rate in the solar neighbourhood, respectively. Taking into account the statistical dispersion around the mean, we miss the observed heating rate by more than 3 sigma. I observed a general flaring of the disc height in the case of all 7 simulations in the outer parts. The dynamics of the disc in the presence of satellites was also studied in the final two chapters where the selected runs were extended to 4 Gyr. The infall of satellites can be responsible for delaying/advancing the bar-formation, depending on the crossing epoch. The passage influences the bar-formation, if the passage occurs between the end of the shot noise regime T1 (0.75 Gyr) and before the exponential growth T2. The Aq-F2 run with the most massive candidate, induces localised vertical heating in the outer disc with R > 15 kpc. I also observed signatures of radial oscillatory behaviour in the outer disc plane, with features similar to that of the Monoceros ring. Disc warping is prominent after 3 Gyr of evolution, reaching median z coordinate of approximately 4 kpc. The asymmetric m = 1 mode is dominant for R > 15 kpc in the form of vertical motion, with the m = 2 mode influencing the rotation of disc particles.

Item Type: Dissertation
Supervisor: Just, Apl. Prof. Dr. Andreas
Date of thesis defense: 16 November 2016
Date Deposited: 07 Dec 2016 07:05
Date: 2016
Faculties / Institutes: The Faculty of Physics and Astronomy > Dekanat der Fakultät für Physik und Astronomie
Subjects: 520 Astronomy and allied sciences
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