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Structure and evolution of simulated dwarf galaxies and Milky Way satellites in Cold and Warm dark matter models

Frings, Jonas

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The satellite galaxies and dwarf galaxies in the neighborhood of the Milky Way provide us with detailed observations that can be used to test our standard model of cosmology and structure formation, the $\Lambda$CDM model. I present a sample of 27 cosmological hydrodynamical simulations with virial masses between $5\times 10^8$ and $10^{10}\,\Msun$ that are aimed to study the properties of dwarf galaxies before accretion. The simulated galaxies are able to reproduce observed scaling relations like the dispersion - size and metallicity - stellar mass relation. The stochasticity of merger induced star formation causes a large scatter in the stellar mass - halo mass relation. In galaxies of stellar masses below $10^6 \, \Msun$ stellar feedback is unable to affect the dark matter halo and hence those galaxies retain a cuspy profile. A subsample of 7 halos is used as initial conditions for simulations of satellite - host galaxy interactions in a Milky Way mass halo. The mass removal due to tidal forces creates flat stellar velocity dispersion profiles and efficiently decreases the circular velocity at $0.5\,\mathrm{kpc}$ without stripping a large amount of stars. Additionally the stripping seems to happen in a way that effectively steepens the central dark matter density slope. To investigate the effects of warm dark matter on dwarf galaxies and Milky Way satellites I repeat the study in a $3\,\mathrm{keV}$ warm dark matter scenario. I present the simulations of 21 halos in both CDM and WDM. In WDM the critical halo mass for the onset of star formation is shifted towards higher masses, while the simulations that do produce stars, reproduce the same scaling relations as their CDM counterparts. However, WDM seems to delay the bulk star formation, making galaxies in CDM look about $2\,\mathrm{Gyr}$ older. While halo concentrations are significantly lower in WDM, the central dark matter density slope is slightly steeper for the low mass end. For four halos (in WDM and CDM) I present their evolution as Milky Way satellites. In contrast to the CDM halos, WDM halos are stripped more effective due to their lower concentrations. The survival probability for WDM satellites, on the other hand, is not necessarily lower because of their steeper central slope. Again, the WDM as well as CDM satellites end up with very cuspy profiles after being stripped. I come to the conclusion that the predictions from my simulations do not challenge the $\Lambda$CDM compared to current observational data of dwarf galaxies and Milky Way satellites. An observation of a cored density profile in one of the very low mass objects, however, would force us reconsider the dark matter model. Also WDM would not pose a solution to this problem.

Item Type: Dissertation
Supervisor: Macciò, Prof. Dr. Andrea Valerio
Date of thesis defense: 11 July 2018
Date Deposited: 26 Jul 2018 13:02
Date: 2018
Faculties / Institutes: The Faculty of Physics and Astronomy > Dekanat der Fakultät für Physik und Astronomie
Subjects: 520 Astronomy and allied sciences
530 Physics
Uncontrolled Keywords: Cosmology, Galaxy Formation, Dark Matter
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