Theses and Dissertations - Department of Physics & Astronomy

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Bounds on large extra dimensions from the simulation of black hole events at the Large Hadron Collider
(University of Alabama Libraries, 2016) Hou, Shaoqi; Harms, B.; University of Alabama Tuscaloosa
Large extra dimensions were originally proposed to solve the hierarchy problem of the Standard Model (SM) of elementary particle physics. The presence of large extra dimensions dilutes gravity, lowering the Planck scale, while SM particles are required to propagate only in the usual 4 dimensional spacetime, leaving the electroweak scale unchanged. If large extra dimensions exist and they are large enough, the Planck scale may be as low as a few TeV’s, so that the hierarchy problem is solved. A smaller Planck scale will bring about numerous phenomenological consequences; in particular, microscopic black holes may be produced in high-energy particle collisions at this energy scale. The decay of black holes, via the Hawking effect, into elementary particles enables the detection of the black hole events, which can be used to infer the existence of large extra dimensions. In this work, we simulate microscopic black hole formation at the Large Hadron Collider with the black hole event generator CATFISH, and compare the simulation results with the experimental data published by the Compact Muon Solenoid collaboration in 2013 at a center of mass energy $\sqrt{s}= 8$ TeV, corresponding to an integrated luminosity of 12.1 fb$^{-1}$. The goal of this work is to test the large extra dimension model and to determine the value of the Planck scale if large extra dimensions exist. The absence of observed black hole events in the experimental data allows us to set lower bounds on the Planck scale and various parameters related to microscopic black hole formation for a number (3 - 6) of large extra dimensions. Assuming no energy loss during high-energy particle collisions, our analysis sets lower bounds on the fundamental Planck scale ranging from 0.8 TeV to 4.9 TeV for black holes fully decaying into SM particles and 0.5 TeV to 3.0 TeV for black holes settling down to a charge neutral, invisible remnant, depending on the minimum allowed black hole mass at formation. Formation of black holes with mass less than 5.2 TeV to 6.5 TeV (SM decay) and 2.2 TeV to 4.0 TeV (remnant) is excluded at 95\% C.L. Further investigation takes into account the effects of the Generalized Uncertainty Principle (GUP), which is expected to play an important role because the mass of a microscopic black hole is only a few fundamental Planck masses. An analysis similar to the one carried out without including GUP effects reveals smaller lower bounds on the fundamental Planck scale ranging from 0.8 TeV to 1.4 TeV for black holes fully decaying into SM particles, only when $\alpha\ge0.9$, depending on the minimum allowed black hole mass at formation. Therefore, this work constrains not only the sizes of the large extra dimensions and the masses of the microscopic black holes, but also sets the lower limits on the energy scale where the effects of quantum gravity start to become significant.
Coupling semi-analytic models and N-body simulations: a new way of making galaxies and stellar halos
(University of Alabama Libraries, 2017) McCord, Krista; Bailin, Jeremy; University of Alabama Tuscaloosa
Stellar halos give insight into the initial conditions that existed when a host galaxy first formed and provide details on disrupted satellites via their different stellar populations. An algorithm that is computationally inexpensive compared to hydrodynamic simulations is necessary in order to theoretically study the structure and formation of galactic stellar halos in sufficient detail to probe substructure. CoSANG (Coupling Semi-Analytic/N-body Galaxies) is a new computational method that we are developing which couples pure dark matter N-body simulations with a semi-analytic galaxy formation model. At each timestep, results from the N-body simulation feed into the semi-analytic code, whose results feed back into the N-body code making the evolution of the dark matter and baryonic matter dependent on one another. CoSANG will enable a variety of galaxy formation science, including analysis of stellar populations, halo merging, satellite accretion, supermassive black holes, and indirect and direct dark matter detection. In this dissertation, I will describe the new simulation code CoSANG. The results from the extensive testing phase on CoSANG will be presented which indicate CoSANG is properly simulating feedback from galaxies within a dark matter halo. I used this validated code to analyze a CoSANG zoom simulation of a $10^{12} \mathrm{M_{\odot}}$ dark matter halo. Results showed a flatter inner halo near the disk and a more spherical outer halo which is expected when a galaxy exists at the center of a dark matter halo. A comparison is made with a simulation run with the same initial conditions, but with the baryonic component simulated using a hydrodynamic algorithm. The semi-analytic model predicted galaxy types better than the hydrodynamic simulation leading to the conclusion that the CoSANG halo is more accurate. I also present a dark matter direct detection analysis on the CoSANG zoom halo to measure the dark matter velocity distributions and modulation amplitudes. The CoSANG results show that the dark matter velocity distribution does not fit well to a Maxwell Boltzmann distribution and the modulation amplitudes derived indicate an anisotropic dark matter velocity distribution. Future work will include tagging dark matter particles with stellar properties to build and evolve a stellar halo.
Dust mapping of spiral galaxy disks from the Hubble starsmog survey
(University of Alabama Libraries, 2016) Bradford, Sarah; Keel, W. C.; University of Alabama Tuscaloosa
Dust in spiral galaxy disks plays an important role in observations through its interaction with starlight. While arguments have been made in favor of completely opaque spiral disks as a result of the dust (see Valentijn, 1990), most subsequent studies agree that spiral galaxies include both optically thick and optically thin regions. Using the occulting-galaxies technique introduced by White & Keel (1992), we created transmission maps of nine partially overlapped galaxy systems taken from the STARSMOG (STarlight Absorption Reduction through a Survey of Multiple Occulting Galaxies) catalog to probe the optical depth in regions of backlit dust. The measurements of all nine targets show a wide range of opacities, and therefore none of them can be definitively classified as either "optically thick" or "optically thin". In the analysis of the transmission maps of predominantly highly inclined systems, we noticed a distinct edge to the dust structure beyond which no dust was present in the foreground galaxy disk. This radius varied amongst systems but was distinct enough to be measured for three of the systems. The transmission maps also reveal a web-like pattern to the dust structure in some galaxy disks. Four of the targets showed dust structure which not only followed the pitch angle of the spiral arms, but also crossed at other various angles. This web-like pattern was only observed in systems where the foreground galaxy was of Hubble type SBc/Sc/Sbc. While there appears to be no real trend in the statistics of transmission through backlit dust with respect to stellar mass of the galaxies, there does appear to be a correlation with respect to star formation rates. In this nine-system sample, the targets with the least star formation appear more opaque. By continuing this study for the rest of the STARSMOG targets, we will be able to determine how representative this sample is of the entire target set.
Finding fossil galaxy system progenitors using strong gravitational lensing
(University of Alabama Libraries, 2018) Johnson, Lucas Edward; Irwin, Jimmy A.; University of Alabama Tuscaloosa
Fossil galaxy systems have been described as some of the oldest systems in the universe, where the central galaxy has cannibalized most nearby member galaxies over cosmic time. While the progenitors to fossil systems have been predicted to exist in numerical simulations, little effort has gone into locating them until now. The discovery of fossil progenitors in the CASSOWARY catalog of strong gravitational lensing demonstrates that not all fossils are old, and their formation histories are more complex than originally thought. These progenitors have optical characteristics consistent with them being the transition phase between non-fossils and fossils, as we are observing the central galaxies in mid-assembly. We also identify a bias where systems acting as strong gravitational lenses are ~5 times more likely to be seen as fossils than non-lensing systems. Chandra X-ray images of eight CASSOWARY fossil progenitors show them being significantly over-luminous and hotter than comparable non-fossils which could be due to the strong lensing bias in our data, or fossils have characteristically deeper potential wells than non-fossils. Two progenitors were luminous enough to see a rise in gas temperature toward their cores which suggests these may be undergoing group mergers akin to the previously studied progenitor CSWA 2 verifying this as a viable fossil formation mechanism. Refinements to our original CASSOWARY data using the Hubble Space Telescope allowed us to disentangle complex merging environments at the centers of these eight progenitors, which further solidified the notion that progenitors are indeed transitioning toward fossil systems.
Investigating the effects of progenitor metallicity on observable features of chandrasekhar mass type ia supernovae and improving detonation models of sub-chandrasekhar mass type ia supernovae
(University of Alabama Libraries, 2018) Miles, Broxton Jake; Townsley, Dean M.; University of Alabama Tuscaloosa
Type Ia Supernovae are generally considered to be the result of the thermonuclear disruption of carbon oxygen white dwarfs. However, the exact mechanism behind the explosion remains uncertain. The pre-explosion progenitor of a white dwarf has never been observed, so all conclusions must be drawn from comparisons between observed events and computational models. Here, work is presented on identifying spectral features indicative of progenitor metallicity. Metallicity affects the production of alpha-chain elements, which leaves imprints in the spectra. Two features are found that may be signals of progenitor metallicity, a Ti feature at 4200 \AA\ and an Fe feature at 5500 \AA . The second portion of this work focuses on the accurate modeling of detonations in sub-Chandrasekhar mass type Ia supernovae. The scales of the burning processes involved, compared to the size of the white dwarf, make fully resolving the detonation computationally impossible in full-star simulations. To mitigate this problem, past studies have used sub-grid scale models that attempt to capture the energetics of the explosion and post-process the results to calculate their models' nucleosynthetic products. If sub-grid models are to be believed, they must have accurate treatments of detonation physics such as curvature and shock strengthening. In low-density regions of the white dwarf, the curvature of the detonation front slows its propagation, affecting the production of intermediate mass elements. We find that the sharp density gradient in the outer radii of the white dwarf counteracts the weakening effect of curvature, resulting in more complete burning than expected in this low density region.
Quantitative analysis of 3-arm spiral galaxies
(University of Alabama Libraries, 2019) Hancock, Colin; Keel, William C.; University of Alabama Tuscaloosa
A relatively small fraction of spiral galaxies has three spiral arms. It has been theorized that these "3-arm spirals" are relatively unstable and prone to decaying into even numbered patterns due to tidal interactions. We present a series of quantitative analyses on a large sample of 3-arm spiral galaxies selected by the Galaxy Zoo 2 group. Much of this analysis used the image processing interface known as the Spiral Arc Finder and Reporter (SpArcFiRe). This program traced spiral arms on submitted images of galaxies and provided information that allowed us to replicate the arms in another program like MS Excel. Most of our work involved images taken from the Sloan Digital Sky Survey (SDSS), supplemented with high-resolution Hubble Space Telescope (HST) observations. This allowed us to study the morphological demographics of our sample, for both the internal structure and arm symmetry. The HST images provided special insight into spiral structure and star formation for these galaxies. We analyzed the star formation in particular using the MIRA AL software for photometry. We also attempted in improve the signal-to-noise of our images using data from the Stripe 82 region of SDSS. Unexpectedly, 3-arm patterns coexist with strong central bars roughly as often as other spiral patterns. We also found that 3-arm spirals do not preferentially exist in low-density regions and may be triggered by interactions.
Simulating dwarf-dwarf galaxy flyby interactions
(University of Alabama Libraries, 2018) Timsina, Ashok; Bailin, Jeremy; University of Alabama Tuscaloosa
This thesis presents the N-body simulation results for the interaction between two equal mass dwarf galaxies. We studied how flyby interactions can cause a different level of disturbance on the dwarf galaxies with the help of four different simulations and measured the departure from their equilibrium state during the interactions. We performed the simulations using N-body code ChaNGa. Initially, we make sure that the interacting galaxies are in an equilibrium state separated by 100 kpc. We established the motion of one galaxy towards another galaxy, which is at rest. We designed the interactions to be increasingly strong by setting the components of velocity and finally we studied the distortion on the galaxies by using Fourier analysis looking at modes m = 1 and m = 2. This analysis allowed us to determine the minimum tidal force required for galaxy distortion.
A study of white dwarfs: cataclysmic variables and double-detonation supernovae
(University of Alabama Libraries, 2019) Caldwell, Spencer; Townsley, Dean M.; University of Alabama Tuscaloosa
Novae, be it classical, dwarf, or supernovae, are some of the most powerful and luminous events observed in the Universe. Although they share the same root, they are produced by different physical processes. We research systems capable of experiencing novae with the intention of furthering our understanding of these astrophysical phenomena. A cataclysmic variable is a binary star system that contains a white dwarf with the potential of undergoing classical or dwarf novae. A recent observation of a white dwarf within one of these systems was found to have an unusually high surface temperature for its orbital period. The discovery contradicts current evolutionary models, motivating research to determine a theoretical justification for this outlier. Using MESA (Modules for Experiments in Stellar Astrophysics), we simulated novae for a progenitor designed to represent a white dwarf in an interacting binary. We developed post-novae cooling timescales to constrain the temperature value. We found the rate at which classical novae cool post-outburst (< 1 K yr−1) is in general agreement with the four−year follow-up observation (∼ 2 K). The evolution of white dwarfs during double- detonation type Ia supernovae was also studied. The progenitors capable of producing these events are not fully established, requiring a consistent model to be developed for parametric analysis. Three improvements were made to the simulation model used in (Townsley et al., 2019): the inclusion of a de-refinement condition, a new particle distribution, and a burning limiter. The focus here was to enhance the computational efficiency, offer better representation of particles in the supernova ejecta, and control the nuclear energy release. These developments were employed to test double-detonation scenarios capable of producing spectra analogous to type Ia supernovae, which will offer insight into their prevalence and strengthen their use in measuring cosmological distance.

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Browsing Theses and Dissertations - Department of Physics & Astronomy by Author "Bailin, Jeremy"

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