The structure of dark matter haloes in cosmological simulations

• Main Author: Bett, Philip Edward
• Published: Durham University 2008
• Subjects: 530
• Online Access: http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.529681

We study the angular momentum, shape and density structures of dark matter haloes using very large dark matter simulations, and use smaller, higher-resolution simulations to investigate how the distributions of these properties are changed by the physical processes associated with baryons and galaxy formation. We begin with a brief review of the necessary background theory, including the growth of cosmic structures, the origin of their angular momenta, and the techniques used to simulate galaxies, haloes and the large scale structure. In Chapter 2, we use the Millennium Simulation (MS) to investigate the distributions of the spin and shape parameters of millions of dark matter haloes. We compare results for haloes identified using three different algorithms, including one based on the branches of the halo merger trees. In addition to characterising the relationships between halo spin, shape and mass, we also study their impact on halo clustering and bias. We go on in Chapter 3 to investigate the internal angular momentum structure of dark matter haloes. We look at the radial profiles of the dark matter angular momentum in terms of both magnitude and direction, again using large-volume dark matter simulations including the MS. We then directly compare dark matter haloes simulated both with and without baryonic physics, studying how this changes the dark matter angular momentum. After relating the spin orientation of galaxies to their haloes, we consider the shape of the projected, stacked mass distribution of haloes oriented according to their central galaxy, mimicking attempts to measure halo ellipticity by weak gravitational lensing. We consider the density structure of dark matter haloes in Chapter 4. For the dark matter simulations, we focus our interest on the source of the scatter in the distribution of concentration parameters, correlating it with both the halo spin and formation time. We compare different algorithms for predicting the concentration distribution using different aspects of the merger histories. We again go on to directly compare high-resolution haloes in simulations run with and without baryons and galaxy formation, looking at how these additional physical processes transform the density profiles. Finally, we compare the circular velocity curves of the haloes simulated with galaxies to the rotation curves of observed galaxies, using the Universal Rotation Curve model.