Physics and Astronomy Electronic Theses and Dissertations (UMKC)
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The items in this collection are the theses and dissertations written by students of the Department of Physics and Astronomy. Some items may be viewed only by members of the University of Missouri System and/or University of Missouri-Kansas City. Click on one of the browse buttons above for a complete listing of the works.
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Item Shocks & fronts in the merging x-ray bright cluster Abell 2219(2025) Huber, Joe (Graduate student in physics); Rulis, Paul Michael, 1976-We present a deep 470 ks Chandra observation of Abell 2219, a very hot and X-ray luminous cluster experiencing a major merger event. Abell 2219, at a redshift of z = 0.225, is only the second galaxy cluster merger where both the forward and reverse shock fronts are identified with X-ray temperature and density measurements (Russell et al., 2012, the other is Abell 2146) and one of only a handful with any shock fronts unambiguously detected as both temperature and density discontinuities. The reason for this rarity is the requirement of a near plane-of-sky merger, to mitigate the effects of projection, and also the inherently low X-ray surface brightness of shocked regions in the outskirts of clusters. Nonetheless, these sharp discontinuities, along with cluster cold fronts, have the potential to illuminate the micro-scale transport processes occurring in the hot intracluster medium. Abell 2219 is also one of the hottest and most X-ray luminous galaxy clusters known, with a system temperature of 12 keV, and unusually, a hot yet dense core, suggesting evidence for ongoing shock activity at the core. It hosts a bright radio halo and three strong radio galaxies. Previous Chandra observations have revealed this system is in the early throes of a violent merger. In this work we present the development of data reduction and analysis pipelines to process our high spatial-resolution, deeper X-ray data, allowing us to confirm the presence of of both shocks and cold fronts within the cluster merger.Item Electronic band structure variations in photothermal catalytic materials(2025) Vanderslice, Jennifer Kylie; Rulis, Paul Michael, 1976-Novel photothermal catalytic devices based on layered semiconductors have great promise as efficient overall water splitting devices for hydrogen production, which can help make H2 into an economically viable alternative to fossil fuels. The effectiveness of the proposed device is sensitively influenced by both the electronic structure of the materials and their interfaces. Yet, the electronic band structure of many of these materials under thermal expansion is under explored. In this study we calculate the electronic structures of a select group of sulfide semiconductors and their lattice thermal expansions, focusing on key parameters such as their band gaps, valence band edges, and conduction band edges. The materials (CoS₂, CoAsS, FeS₂) were selected for their simple structures, lower electron numbers and increasing band gaps compared to each other. By calculating band structures along a universal high-symmetry path in k-space, we can compare how temperature induced asymmetric lattice changes impact the electronic properties of the different materials and the overall stability of the proposed photothermal catalytic device. These insights help identify what materials can function reliably at higher temperatures without compromising charge separation or light absorption, two important factors in water splitting performance. This approach provides valuable insights into optimizing materials for efficient photothermal catalytic devices and guides future designs for water splitting applications.Item Quenching mechanisms in recently quenched elliptical galaxies: insights from neutral hydrogen studies and environmental analysis(2025) Deo, Deepak Kumar; Rulis, Paul Michael, 1976-; Schlein, CandaceRecently Quenched Elliptical galaxies (RQEs) represent a critical phase in the transition from star-forming to quiescent galaxies. However, the mechanisms driving their quenching remain elusive. We conduct a multi-wavelength analysis of 695 RQEs, along with their precursors (preRQEs) and descendants (postRQEs), focusing on their neutral hydrogen (HI) content and star formation properties. Contrary to conventional quenching models emphasizing gas depletion, RQEs retain substantial HI reservoirs (fgas ≥ 17%), suggesting that quenching is not primarily driven by gas exhaustion. We identify a critical halo mass threshold at log(Mhalo) = 12.1 M⊙, delineating different evolutionary pathways for RQEs. This threshold aligns with the transition from cold-mode to hot-mode gas accretion in theoretical models. RQEs in lower-mass halos (log Mhalo < 12.1M⊙) likely experience rapid quenching, possibly initiated by major mergers, followed by brief AGN activity and sustained LINER emission. We propose two evolutionary pathways: (a) rapid quenching via major mergers followed by AGN/LINER activity and passive evolution, and (b) rapid quenching followed by rejuvenation through minor mergers before evolving into more massive, long-term quenched ellipticals. These results challenge the conventional understanding of galaxy quenching, especially in low-density environments where RQEs typically reside. Our findings suggest that while RQEs may follow a rapid quenching pathway, their evolution is influenced by interactions between gas accretion modes, feedback mechanisms, and environmental factors. Future observations with advanced radio interferometers like SKA will be crucial for elucidating the quenching mechanisms in RQEs and their role in galaxy evolution.Item Infrared-Bright Active Galactic Nuclei in Massive Galaxy Clusters(2024) Floyd, Benjamin, 1989-; Brodwin, Mark; Bani-Yaghoub, MajidThe number of active galactic nuclei (AGN) in galaxy clusters has been observed to grow by nearly two orders of magnitude from the local universe to z ~ 1.5. Star formation rates in clusters have also been observed to rise rapidly over this redshift interval. These trends, along with several other recent observations of high-redshift clusters, have led to the idea that this enhanced star formation and AGN activity may be driven by galaxy mergers within the clusters. Since mergers are more efficient in lower mass clusters with smaller galaxy velocity dispersions, the expectation is that AGN incidence should scale inversely with cluster mass. A recent study using X-ray selected AGN has offered some support for this model in low-redshift clusters, though with large uncertainties. We select infrared bright AGN from a large, uniform, mass-selected galaxy cluster sample from the South Pole Telescope spanning a redshift range of 0.15 ≲ z ≲ 1.7 for which we have acquired follow-up Spitzer Space Telescope observations. With these data we explore the incidence of IR-bright AGN in clusters as a function of cluster mass, redshift, and projected cluster-centric radius.Item Toward high thermoelectric performance of solids: ab initio forces within the orthogonalized linear combination of atomic orbitals method(2024) Alzahrani, Nuha; Rulis, Paul Michael, 1976-; Peng, Zhonghua, Ph. D.Toward the long-term goal of predicting the figure of merit of complex thermoelectric materials, we introduce the computational and theoretical groundwork for the calculation of interatomic forces in ab initio calculations using the Orthogonalized Linear Combination of Atomic Orbitals (OLCAO) method. The approach is based on the Hellmann-Feynman (HF) theorem and Pulay forces in the presence of an atomic orbital basis set. To accomplish this, we offered a thorough derivation of a HF theorem that holds for all quantum mechanical systems. This theorem serves as a valuable tool for understanding the nature of chemical bonding in quantum chemistry and solid-state physics. We follow Pulay's suggestion [Mol. Phys.17, 153 (1969)] to update the HF theorem by including contributions from changes in the wave function with respect to nuclear sites. Additionally, we developed the Obara–Saika scheme for evaluating the derivative of different molecular integrals that contribute to the HF force using Gaussian-type orbitals, i.e., electron repulsion integrals, kinetic energy integrals, and nuclear attraction integrals. Once the force calculation was implemented in the OLCAO method, we applied this method to compute the interatomic forces between various pairs of atoms in diatomic molecules such as N2, H2, O2, F2, Cl2, I2, CO, and NO.