자료유형  

 학위논문

Control Number  

0017160115

International Standard Book Number  

9798382775227

Dewey Decimal Classification Number  

530

Main Entry-Personal Name  

Liu, Xin.

Publication, Distribution, etc. (Imprint  

[S.l.] : The University of Chicago., 2024

Publication, Distribution, etc. (Imprint  

Ann Arbor : ProQuest Dissertations & Theses, 2024

Physical Description  

143 p.

General Note  

Source: Dissertations Abstracts International, Volume: 85-12, Section: B.

General Note  

Advisor: Habib, Salman.

Dissertation Note  

Thesis (Ph.D.)--The University of Chicago, 2024.

Summary, Etc.  

요약In cosmological models of hierarchical structure formation, small primordial density fluctuations grow to eventually collapse under gravity and finally form halos dominated by dark matter. Cosmological simulations play a key role in studying structure formation especially on non-linear scales where analytical predictions are very challenging. This thesis presents three studies which focus on early and late stages of cosmic structure formation.We first use the density power spectrum as a probe to investigate non-collisional numerical discreteness errors in two-species cosmological N-body simulations. When initializing both species with the same total matter transfer function, biased power growth is measured on small scales if the solver force resolution is set to be finer than the mean interparticle separation. Significant large-scale power offsets are found from simulations with conventional offset grid initial conditions when individual transfer functions are applied to each species. These offsets still exist when the two species are designated with the same mass, implying the error does not come from the unequal particle mass but rather the discreteness in the total matter field. Two mitigation strategies are presented to address discreteness errors: the frozen potential method and softened inter-species short-range forces. Both mitigation strategies shows notable improvements in large-scale offsets by approaching the continuum limit.We then turn to dark matter halos in "Last Journey", a gravity-only cosmological simulation, with the aim of resolving questions regarding "too big to fail" substructure in group-scale halos, by studying the properties of fossil groups. Fossil groups are typically distinguished by high X-ray brightness and a large luminosity gap in the group between the brightest and second brightest galaxy. We exploit halo merger tree information to suggest two parameters: a luminous merger mass threshold and a last luminous merger redshift cut-off, in order to identify fossil group candidate halos. Our assumptions give rise to early formation, higher concentrations, and more relaxed fossil group candidates in contrast to other halos within the same mass range.The final project is a study of halo structure and how it can affect observations based on gravitational lensing. Current descriptions of dark matter halos often assume a specific form of the density profile and apply parametric fitting methods. We utilize Gaussian Processes, a non-parametric machine learning method to determine the spatial distribution of matter in halos and obtain a more robust understanding of halo profiles. Stable and smooth descriptions of halos are produced by this procedure which leads to more reliable results. We present a detailed study of halo profile fitting as well as classify halos into various sub-types based on the fitting results. This classification, which considers types of relaxed and unrelaxed halos, is useful to understand selection effects in surveys that use strong gravitational lensing to identify group and cluster scale halos.

Subject Added Entry-Topical Term  

Physics.

Subject Added Entry-Topical Term  

Computational physics.

Subject Added Entry-Topical Term  

Astrophysics.

Index Term-Uncontrolled  

Cosmology

Index Term-Uncontrolled  

Dark matter

Index Term-Uncontrolled  

Halos

Index Term-Uncontrolled  

Gravitational lensing

Index Term-Uncontrolled  

Cosmic structure formation

Added Entry-Corporate Name  

The University of Chicago Physics

Host Item Entry  

Dissertations Abstracts International. 85-12B.

Electronic Location and Access  

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Control Number  

joongbu:657860