Title
Analytical and numerical studies of dark matter halos
Abstract
This dissertation focuses on the evolution and structure of dark matter halos of
galaxies, groups and clusters of galaxies. I explore the dependence of the final halo’s
properties on the initial conditions and the physical processes that guide the halo to
equilibrium, with special focus on the power-law nature of the ρ/σ3 profile, where ρ is
the density profile and σ is the velocity dispersion profile. As the astronomy community
does not yet fully understand these processes, this research expands our understanding
of collisionless, gravitationally-interacting systems.
In the initial chapters, I study the collisionless semi-analytic halo simulations and
show that the final properties are sensitive to the initial conditions, such as the powerspectra
filtering scale, the secondary velocities’ magnitudes and directions, and the
accretion rate. The general conclusions are that semi-analytic halos are in hydrostatic
equilibrium and have a power-law ρ/σ3 profile. If there were discontinuities in the
initial conditions, the power-law feature in ρ/σ3 breaks. Because of this, hydrostatic
equilibrium is a less restrictive condition than the ρ/σ3 profile. These halos can recover
from moderate discontinuities by either correcting a single profile by sacrificing other
quantities or by sufficient post-accretion.
Finally, I compare collisionless semi-analytic and N-body simulations directly. This
novel comparison is useful because these techniques use different physics to collapse
the proto-halo. The physical differences between these two methods are used to determine
causes of the final halo profiles. Specifically, I find the NFW density profile
and power-law ρ/σ3 are due to the slow rate of evolution, which is determined from
the initial conditions and cosmology. The density slope-velocity anisotropy relationship
is dependent, rather, on the physical processes (notably the radial orbit instability)
and three-dimensional evolution used to collapse the proto-halos. We also find that
the slow-evolution halos do not undergo violent relaxation (large changes in the global potential). Thus we suggest that slow, collisionless relaxation is responsible for creating
the power-law feature ρ/σ3.
Description
University of Minnesota Ph.D. dissertation. December 2008.Major: Astrophysics. Advisor: Liliya L.R. Williams. 1 computer file (PDF); xx 155 pages.
Suggested Citation
Austin, Crystal Gayle.
(2008).
Analytical and numerical studies of dark matter halos.
Retrieved from the University of Minnesota Digital Conservancy,
https://hdl.handle.net/11299/46908.