ASU Electronic Theses and Dissertations
This collection includes most of the ASU Theses and Dissertations from 2011 to present. ASU Theses and Dissertations are available in downloadable PDF format; however, a small percentage of items are under embargo. Information about the dissertations/theses includes degree information, committee members, an abstract, supporting data or media.
In addition to the electronic theses found in the ASU Digital Repository, ASU Theses and Dissertations can be found in the ASU Library Catalog.
Dissertations and Theses granted by Arizona State University are archived and made available through a joint effort of the ASU Graduate College and the ASU Libraries. For more information or questions about this collection contact or visit the Digital Repository ETD Library Guide or contact the ASU Graduate College at gradformat@asu.edu.
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- All Subjects: Astrophysics
Description
The distribution of galaxies traces the structure of underlying dark matter, and carries signatures of both the cosmology that evolved the universe as well as details of how galaxies interact with their environment and each other. There are many ways to measure the clustering of galaxies, each with unique strengths, uses, theoretical background, and connection to other physical concepts. One uncommon clustering statistic is the Void Probability Function (VPF): it simply asks, how likely is a circle/sphere of a given size to be empty in your galaxy sample? Simple and efficient to calculate, the VPF is tied to all higher order volume-averaged correlation functions as the 0$^{\text{th}}$ moment of count-in-cells, and encodes information from higher order clustering that the robust two-point correlation function cannot always capture. Using simulations of Lyman-alpha emitting galaxies across either redshift history or the epoch of reionization, this work asks: how powerful is the VPF itself? When can and should it be used for galaxy clustering? What unique constraints or guidelines can it give for the pacing of reionization, in the Lyman-$\alpha$ Galaxies in the Epoch of Reionization (LAGER) narrowband survey or across the Roman Space Telescope grism? This work provides practical guidelines for creating and carrying out clustering studies using the the VPF, and motivates the use of the VPF for reionization. The VPF of LAEs can complement LAGER constraints for the end of reionization, and thoroughly inform the timing and pace of reionization with Roman.
ContributorsPerez, Lucia Alexandra (Author) / Malhotra, Sangeeta (Thesis advisor) / Butler, Nathaniel (Thesis advisor) / Groppi, Christopher (Committee member) / Scannapieco, Evan (Committee member) / Rhoads, James E (Committee member) / Arizona State University (Publisher)
Created2022
Description
Building on the legacies of Planck and the Atacama Cosmology Telescope, among others, future cosmic microwave background (CMB) observatories are poised to revolutionize our understanding of the cosmos by implementing proven detector systems at scales previously incomprehensible. Leading the charge is Simons Observatory (SO), a suite of four telescopes located at 5,200 meters elevation in the Atacama Desert of Chile. With more than 60,000 transition-edge sensor (TES) detectors deployed in six frequency bands across three half-meter telescopes and one 6-meter telescope, SO will observe CMB temperature and polarization at small and large scales with greater sensitivity and control over systematics than has yet been achieved. In deploying more detectors than all other previous CMB experiments combined, SO must also chart new territory in the realm of TES readout. Breakthroughs in microwave multiplexing (μ-mux) readout technology now allow the simultaneous readout of approximately 1,000 detectors on a single set of cables, far surpassing the capabilities of previous systems. For the Large Aperture Telescope’s >30,000 detectors, this translates to a total of just 45 input/output lines. A crucial piece of the SO readout architecture is the Universal Readout Harness (URH), a "plug-and-play" assembly that contains the 300K-4K elements. Configurable to support the readout requirements of each receiver, each URH can support up to 24 readout lines. In addition to the radiofrequency (RF) components, the URH can also support up to 12x50-wire DC cable looms, which provide detector and amplifier power. This dissertation describes the construction and testing of the 6 URHs required for nominal SO operations, as well as the on-site integration of the first Small Aperture Telescope. Separately, an optical stacking analysis of quiescent galaxies at z~1 using images from the Dark Energy Survey is presented. Motivated by a desire to better understand the evolution of massive elliptical galaxies, high signal-to-noise images generated from averaging ~100,000 individual galaxy cutouts are used to calculate surface brightness profiles in the grizY bands. Additionally, the extragalactic background light is derived from these stacks and is found to be in good agreement with previous measurements.
ContributorsMoore, Jenna Elizabeth (Author) / Mauskopf, Philip D (Thesis advisor) / Groppi, Christopher (Committee member) / Scannapieco, Evan (Committee member) / Cohen, Seth (Committee member) / Arnold, Kam (Committee member) / Arizona State University (Publisher)
Created2023
Description
TolTEC is a three-band millimeter-wave, imaging polarimeter installed on the 50 m diameter Large Millimeter Telescope (LMT) in Mexico. This camera simultaneously images the focal plane at three wavebands centered at 1.1 mm (270 GHz), 1.4 mm (214 GHz), and 2.0 mm (150 GHz). TolTEC combines polarization-sensitive kinetic inductance detectors (KIDs) with the LMT to produce high resolution images of the sky in both total intensity and polarization. I present an overview of the TolTEC camera’s optical system and my contributions to the optomechanical design and characterization of the instrument. As part of my work with TolTEC, I designed the mounting structures for the cold optics within the cryostat accounting for thermal contraction to ensure the silicon lenses do not fracture when cooled. I also designed the large warm optics that re-image the light from the telescope, requiring me to perform static and vibration analyses to ensure the mounts correctly supported the mirrors. I discuss the various methods used to align the optics and the cryostat in the telescope. I discuss the Zemax optical model of TolTEC and compare it with measurements of the instrument to help with characterization. Finally, I present the results of stacking galaxies on data from the Atacama Cosmology Telescope (ACT) to measure the Sunyaev-Zel’dovich (SZ) effect and estimate the thermal energy in the gas around high red-shift, quiescent galaxies as an example of science that could be done with TolTEC data. Since the camera combines high angular resolution with images at three wavelengths near distinct SZ features, TolTEC will provide precise measurements to learn more about these types of galaxies.
ContributorsLunde, Emily Louise (Author) / Mauskopf, Philip (Thesis advisor) / Groppi, Christopher (Committee member) / Scannapieco, Evan (Committee member) / Noble, Allison (Committee member) / Bryan, Sean (Committee member) / Arizona State University (Publisher)
Created2023
Description
Direct imaging is a powerful tool in revealing the architectures of young planetary systems, clearly showing the structure of circumstellar disks. Circumstellar disks, similar to the asteroid belt, are critical elements of any planetary system, and the study of them is important to understanding planet formation. Disks around several main sequence stars have already been observed directly interacting with exoplanets in their respective systems. Imaging can help answer many of the key questions of how disks interact in their respective systems. The Gemini Planet Imager is a high contrast imaging instrument that has spatially resolved several circumstellar disks for the first time, many exhibiting tracers of ongoing planet formation or the presence of a perturbing exoplanet. With this new sample, population analyses of characteristics of disks can now be explored and compared to information at other wavelengths. Direct imaging is also a uniquely accessible tool in engaging students and the community in astronomy. In combination with a course-based undergraduate research experience, direct imaging has the ability to engage students in the process of doing research in a very accessible manner. In Chapter 1, I introduce the concepts related to circumstellar debris disks, further focusing on the sub-field of direct imaging and its value in understanding these systems and engaging students in astronomy. In Chapter 2, I present four images of newly-resolved debris disks in the Scorpius-Centaurus association, comparing their characteristics with many other spatially-resolved circumstellar disks within the moving group. In Chapter 3, I present a uniform analysis of debris disk structure using a consistent and empirically-informed modeling approach. In Chapter 4, I present my findings and experiences in developing and teaching a course-based undergraduate research experience for students in the country’s first online astronomy degree program centered on the direct imaging of brown dwarfs. In Chapter 5, I present my conclusions on the topics I have investigated and discuss future work within the field of direct imaging and its role in driving astronomy research and education forward.
ContributorsHom, Justin (Author) / Patience, Jennifer (Thesis advisor) / Knierman, Karen (Committee member) / Scowen, Paul (Committee member) / Simon, Molly (Committee member) / Young, Patrick (Committee member) / Arizona State University (Publisher)
Created2023
Description
Most stars in our galaxy are M–dwarfs, much cooler and smaller than the sun. The ubiquitous nature of these stars is also paired with the formation of terrestrial exoplanets orbiting them. The strategic placement of M-dwarfs between main-sequence stars and brown dwarfs, their uniqueness as exoplanet analogs, and their dominating presence in the galactic stellar population make them priority targets for study. This work investigates outstanding questions, including the need to acquire constraints on their chemical compositions to decode formation processes, evolution, and interaction with companion objects. Chapter 1 lays out a broad background emphasizing the importance of studying the most populous star in the galaxy, their far-reaching implications, and primarily the numerous challenges in characterizing the atmospheres and environments of these stars. Chapter 2 investigates the influence of M-dwarf star spots propagating into spectra of transiting terrestrial planets, showing that inaccurate modeling of M-dwarf photospheres leads to significant bias when inferring atmospheric properties of companion exoplanets. These biases persist despite correcting M-dwarf spot signatures imprinted onto the exoplanetary spectra, even with high-fidelity JWST observations. This result emphasizes the need for improved stellar atmosphere models as the first step to improving our understanding of the companion planets. To address this, chapter 3 introduces SPHINX—a new stellar atmosphere model grid for M-dwarfs. SPHINX provides improved constraints on fundamental properties of benchmark M-dwarf systems (e.g., temperature, surface gravity, radius, and chemistry). The improvement is significant relative to the state-of-the-art stellar model grid available today. Chapter 4 expands this model, applying it to mid-to-late type M-dwarfs, and investigating chemical trends in their atmospheric properties. Using low-resolution observations, both archival data (from SpeX Prism Library Database) and from previous empirical studies; this chapter presents constraints on fundamental atmospheric properties of 71 low-mass, late-type M-dwarfs to understand spectroscopic degeneracies arising due to stellar activity, cloud/dust condensation and convection. With SPHINX models, the chemical properties of these stars are compared against main-sequence stars to acquire a more holistic understanding of M-dwarfs as a class—in the quest to ultimately characterize their companions.
ContributorsIyer, Aishwarya (Author) / Line, Michael (Thesis advisor) / Patience, Jennifer (Committee member) / Young, Patrick (Committee member) / Shkolnik, Evgenya (Committee member) / O'Rourke, Joseph (Committee member) / Arizona State University (Publisher)
Created2023
Description
The interactions that take place in the ionized halo of gas surrounding galaxies, known as the circumgalactic medium (CGM), dictates the host galaxy's evolution throughout cosmic time. These interactions are powered by inflows and outflows that enable the transfer of matter and energy, and are driven by feedback processes such as accretion, galactic winds, star formation and active galactic nuclei. Such feedback and the interactions that ensue leads to the formation of non-equilibrium chemistry in the CGM. This non-equilibrium chemistry is implied by observations that reveal the highly non-uniform distribution of lower ionization state species, such as Mg II and Si II, along with widespread higher ionization state material, such as O VI, that is difficult to match with equilibrium models. Given these observations, the CGM must be viewed as a dynamic, multiphase medium, such as occurs in the presence of turbulence. To better understand this ionized halo, I used the non-equilibrium chemistry package, MAIHEM, to perform hydrodynamic (HD) simulations. I carried out a suite of HD simulations with varying levels of artificially driven, homogeneous turbulence to learn how this influences the non-equilibrium chemistry that develops under certain conditions present in the CGM. I found that a level of turbulence consistent with velocities implied by observations replicated many observed features within the CGM, such as low and high ionization state material existing simultaneously. At higher levels of turbulence, however, simulations lead to a thermal runaway effect. To address this issue, and conduct more realistic simulations of this environment, I modeled a stratified medium in a Milky Way mass Navarro-Frenk-White (NFW) gravitational potential with turbulence that decreased radially. In this setup and with similar levels of turbulence, I alleviated the amount of thermal runaway that occurs, while also matching observed ionization states. I then performed magneto-hydrodynamic (MHD) simulations with the same model setup that additionally included rotation in the inner halo. Magnetic fields facilitate the development of an overall hotter CGM that forms dense structures within where magnetic pressure dominates. Ion ratios in these regions resemble detections and limits gathered from recent observations. Furthermore, magnetic fields allow for the diffusion of angular momentum throughout the extended disk and gas cooling onto the disk, allowing for the maintenance of the disk at late times.
ContributorsBuie II, Edward (Author) / Scannapieco, Evan (Thesis advisor) / Borthakur, Sanchyeeta (Committee member) / Groppi, Christopher (Committee member) / Jacobs, Danny (Committee member) / Young, Patrick (Committee member) / Arizona State University (Publisher)
Created2022
Description
In this opus, I challenge the claim that inflationary spacetimes must be past geodesi-cally incomplete. To do this, I utilize the warped product formalism of Bishop and
O’Neill and build upon the venerable Friedmann Robertson Walker (FRW) space-
time formalism to the Generalized Friedmann Robertson Walker (GFRW) spacetime
formalism, where the achronal spacelike sections can be any geodesically complete
Riemannian manifold (Σ, gΣ ). I then solve the GFRW geodesic equation in generality
as a functional of the scale factor f , and derive a main theorem, which characterizes
the geodesic completeness in GFRW spacetimes. After offering a definition of infla-
tion which enumerates the topological requirements which permit a local foliation of
a scale factor, I discuss a cohort of geodesically complete inflationary GFRWs which
have averaged expansion quantity Havg > 0, proving that classical counter-examples
to the theorem of Borde, Guth, and Vilenkin do exist. I conclude by introducing
conjectures concerning the relationship between geodesic completeness and inflation:
in particular, I speculate that if a spacetime is geodesically complete and non-trivial,
it must inflate!
ContributorsLesnefsky, Joseph Edward (Author) / Easson, Damien A (Thesis advisor) / Davies, Paul C (Thesis advisor) / Parikh, Maulik (Committee member) / Kotschwar, Brett (Committee member) / Arizona State University (Publisher)
Created2024
Description
This dissertation presents a comprehensive study on the advancement of astrophysical radio, microwave, and terahertz instrumentation/simulations with three pivotal components.First, theoretical simulations of high metallicity galaxies are conducted using the supercomputing resources of Purdue University and NASA. These simulations model the evolution
of a gaseous cloud akin to a nascent galaxy, incorporating variables such as kinetic energy,
mass, radiation fields, magnetic fields, and turbulence. The objective is to scrutinize the
spatial distribution of various isotopic elements in galaxies with unusually high metallicities and measure the effects of magnetic fields on their structural distribution.
Next, I proceed with an investigation of the technology used for reading out Microwave Kinetic Inductance Detectors (MKIDs) and their dynamic range limitations tied to the current
method of FPGA-based readout firmware. In response, I introduce an innovative algorithm
that employs PID controllers and phase-locked loops for tracking the natural frequencies
of resonator pixels, thereby eliminating the need for costly mid-observation frequency recalibrations which currently hinder the widespread use of MKID arrays.
Finally, I unveil the novel Spectroscopic Lock-in Firmware (SpLiF) algorithm designed to
address the pernicious low-frequency noise plaguing emergent quantum-limited detection
technologies. The SpLiF algorithm harmonizes the mathematical principles of lock-in amplification with the capabilities of a Fast Fourier Transform to protect spectral information
from pink noise and other low-frequency noise contributors inherent to most detection systems. The efficacy of the SpLiF algorithm is substantiated through rigorous mathematical
formulation, software simulations, firmware simulations, and benchtop lab results.
ContributorsHoh, Jonathan (Author) / Groppi, Christopher E (Thesis advisor) / Jamison-Hooks, Tracee (Committee member) / Buie II, Edward (Committee member) / Trichopoulos, Georgios (Committee member) / Scannapieco, Evan (Committee member) / Arizona State University (Publisher)
Created2024