PhD thesis,
The Structure of Dark Matter Haloes in Cosmological Simulations
Institute for Computational Cosmology, University of Durham, (September 2008)
Abstract
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.<p/>
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.<p/>
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.<p/>
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.<p/>
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.
