Astrophysics and Astronomy Commons^™

Bayesian Model Comparisons In Planetary Science, John Henry Boisvert

UNLV Theses, Dissertations, Professional Papers, and Capstones

Model comparison in the modern era allows us to use statistical methods that were previously difficult with older machines. I present a state-of-the-art model comparison code that uses modern Bayesian statistics to measure the Bayes factor between two competing models. The Bayes factor is the ratio of the probability of the data given one model to the probability of the data given another model. My code was used to compare models in five problems in planetary science. The first three pertain to radial velocity exoplanet data. There is a degeneracy in the radial velocity exoplanet signal between a single planet …

Force Multiplier Calculations For X-Ray Binaries And Active Galactic Nuclei, Randall Cody Dannen

UNLV Theses, Dissertations, Professional Papers, and Capstones

Motivated by the work done to explore the winds from hot stars (Lamers & Cassinelli 1999), we develop a method for self consistently calculating force multipliers for Type 1 and Type 2 active galactic nuclei (AGN), soft and hard start X-ray binaries (XRBs) spectral energy distributions (SEDs). We find that the ampflication to the radiation force can be as large as 100 even when the gas is highly ionized due to Fe and O ions. We discuss future efforts to incorporate these findings in magnetohydrodynamic simulations.

Primordial Black Holes In The Cosmological Context And Transient Electromagnetic Signatures From Merging Black Hole Binaries, Jared Robert Rice

UNLV Theses, Dissertations, Professional Papers, and Capstones

The cosmological evolution of primordial black holes (PBHs) is presented via analysis of the accretion and evaporation histories of the holes. The ultimate end of any BH is evaporation — a spectacular seconds-long burst of high-energy radiation and particles. The critical initial mass of a PBH undergoing current era evaporation is ∼ 510 trillion grams. A near- critical mass PBH will not accrete radiation or matter in sufficient quantity to retard its inevitable evaporation, if the hole remains within an average volume of the universe. The gravitational waves (GWs) from five BH binary merger events discovered by the LIGO/Virgo collaborations …

Exterior Giant Planet Effects On Terrestrial Architecture, Anna Corinne Childs

UNLV Theses, Dissertations, Professional Papers, and Capstones

Terrestrial planet formation is a chaotic and violent process which is not fully understood. Prior to Kepler, Solar System observations were the basis for planet formation models. How- ever, Kepler observations have shown that exoplanet systems are very different from our solar system, thus requiring a more complete planet formation model. With advancements in com- putational ability, N-body integrators, and collision models, we can explore planet formation by experimenting with simulations in different parameter space. Our Solar System has shown us that exterior giant planets can play a vital role in the shaping of the final terrestrial planet system. Our …

Using Two Simulation Tools To Teach Concepts In Introductory Astronomy: A Design-Based Research Approach, Pamela A. Maher

UNLV Theses, Dissertations, Professional Papers, and Capstones

Technology in college classrooms has gone from being an enhancement to the learning experience to being something expected by both instructors and students. This design-based research investigation takes technology one step further, putting the tools used to teach directly in the hands of students. The study examined the affordances and constraints of two simulation tools for use in introductory astronomy courses. The variety of experiences participants had using two tools; a virtual reality headset and fulldome immersive planetarium simulation, to manipulate a lunar surface flyby were identified using a multi-method research approach with N = 67 participants. Participants were recruited …

Probing Broad Line Regions Of Active Galactic Nuclei, Champika Sandamali Weerasooriya

UNLV Theses, Dissertations, Professional Papers, and Capstones

The broad line regions (BLR) of Type I Active galactic nuclei (AGN) are too small to be spatially resolved even with the most powerful telescopes available. Observations suggest that BLR gas is moving under the influence of the gravitational potential of the central supermassive black-hole (SMBH) and responds to the variations in the ionizing continuum flux of the accretion disk, giving rise to broad emission line variations with a time delay. Reverberation mapping campaigns seek to use this time variability to resolve the BLRs in the time domain instead of spatial domain, providing a way to infer geometry and kinematics …

Understanding Progenitors Of Gamma Ray Bursts With Multi-Wavelength Properties, Ye Li

UNLV Theses, Dissertations, Professional Papers, and Capstones

Gamma-ray bursts (GRBs) are among the most brilliant explosions in the universe, named for their intense, seconds-duration $\gamma$-ray emission. They are generally classified into two categories according to the durations of their $\gamma$-ray emission: the long-duration GRBs (LGRBs) with durations more than 2 seconds, and the short-duration GRBs (SGRBs) with durations less than 2 seconds. Most SGRBs are believed to originate from mergers of compact stars (e.g., neutron star-neutron star and neutron star-black hole; also known as Type I GRBs by their physical mechanism), while the LGRBs are thought to originate from core-collapse of massive stars (Type II). In addition …

Secular Resonances During Main-Sequence And Post-Main-Sequence Planetary System Dynamics, Jeremy L. Smallwood

UNLV Theses, Dissertations, Professional Papers, and Capstones

We investigate gravitational perturbations of an asteroid belt by secular resonances. We ap- ply analytic and numerical models to main–sequence and post–main–sequence planetary systems. First, we investigate how the asteroid impact rate on the Earth is affected by the architecture of the planetary system. We find that the nu6 resonance plays an important role in the asteroid collision rate with the Earth. Compared to exoplanetary systems, the solar system is somewhat special in its lack of a super–Earth mass planet in the inner solar system. We therefore consider the effects of the presence of a super–Earth in the terrestrial planet …

The Formation And Dynamics Of Clouds In The Environment Of Active Galactic Nuclei, Timothy Waters

UNLV Theses, Dissertations, Professional Papers, and Capstones

Active galactic nuclei (AGN) are among the most luminous objects in the universe and are known to be powered by accretion onto supermassive black holes in the centers of galaxies. AGN clouds are prominent components of successful models that attempt to unify the diversity of AGN. These clouds are often hypothesized to be the source of the broad and narrow line emission features seen in AGN spectra. Moreover, the high column densities of gas needed to account for broad absorption lines has been attributed to the same population of clouds, while the motion of AGN clouds has been invoked to …

Study The Mechanism Of The Prompt Emission Of Gamma-Ray Bursts, Wei Deng

UNLV Theses, Dissertations, Professional Papers, and Capstones

The prompt emission of Gamma-Ray Bursts (GRBs) has been detected over 40 years, but the mechanism of the prompt emission is still a mystery. The problem can be summarized as several debatable questions: What is the energy composition of the jets/outflows? What is the energy dissipation mechanism? How are the particles accelerated during the energy dissipation process? What is the radiation mechanism to produce the observed prompt emission? In order to solve these problems, several theoretical models have been proposed, including the classical "internal shock (IS)" model, the "dissipative photosphere" model, the "magnetic dissipation" model, and so on. Different models …

Constraining The Progenitor And Central Engine Of Gamma-Ray Bursts With Observational Data, Lu Houjun

UNLV Theses, Dissertations, Professional Papers, and Capstones

Gamma-ray bursts (GRBs) are extremely energetic explosions at cosmological distances. We have made great progress in understanding the mysteries of these events since they were discovered more than forty years ago. However, some open questions still remain, e.g. how many classes of GRBs are there, what are the progenitors of these classes, and what is the central engine powering these huge explosions? Thanks to the NASA missions Swift and Fermi, which are used to detect the multi-wavelength emission from these transients, our understanding of GRBs has been greatly advanced. In this dissertation, I use multi-wavelength data to constrain the progenitor …

Mars-Relevant Phosphate Minerals And Implications For Martian Habitability, Christopher Adcock

UNLV Theses, Dissertations, Professional Papers, and Capstones

This dissertation is comprised of three studies focused on martian phosphate availability, with an introductory chapter introducing and linking the three studies. Chapter two is on the subject of merrillite synthesis. Merrillite is an extraterrestrial Ca-phosphate mineral similar to the mineral whitlockite and is found as a dominant primary phosphate mineral in martian meteorites. The chapter includes methods of whitlockite and merrillite synthesis as well as a detailed characterization of the produced minerals and a mechanism by which charge balance can be maintained when merrillite is synthesized through dehydrogenation of whitlockite.

Chapter three presents the results of kinetic and thermodynamic …

A Physically-Based Type Ii Supernova Feedback Model In Sph Simulations, Keita Todoroki

UNLV Theses, Dissertations, Professional Papers, and Capstones

We implement and test a core-collapse Type II SN feedback that is physically motivated and produces good agreement with observations in galaxy formation simulations. The model includes both kinetic and thermal feedback, allowing wind particles to receive a velocity kick that mimics galactic winds and distributes mass and metallicity to the interstellar and intergalactic medium. We also include a phenomenological stellar feedback to study a possible enhancement of the efficiency of the SN-II feedback by creating lower-density ambient gas medium of the stellar populations by distribution of thermal energy. Our SN-II model is unique in the sense that it computes …

Physics Of Gamma-Ray Bursts And Multi-Messenger Signals From Double Neutron Star Mergers, He Gao

UNLV Theses, Dissertations, Professional Papers, and Capstones

My dissertation includes two parts:

Physics of Gamma-Ray Bursts (GRBs): Gamma-ray bursts are multi-wavelength transients, with both prompt gamma-ray emission and late time afterglow emission observed by telescopes in different wavelengths. I have carried out three investigations to understand GRB prompt emission and afterglow. Chapter 2 develops a new method, namely, "Stepwise Filter Correlation" method, to decompose the variability components in a light curve. After proving its reliability through simulations, we apply this method to 266 bright GRBs and find that the majority of the bursts have clear evidence of superposition of fast and slow variability components. Chapter 3 gives …

How Accurately Can The Inclination Angle, Position Angle, And Location Of The Dynamic Center Be Measured From The Neutral Hydrogen Disk In The Central Regions Of Dwarf Galaxies?, John Henry Boisvert

UNLV Theses, Dissertations, Professional Papers, and Capstones

Rotation curves measured using Hi emission are a powerful tool for probing the mass distribution of galaxies. We investigate the accuracy with which rotation curves can be determined using the tilted-ring model. We have examined the effect of varying the dynamic center on measured rotation velocities within the inner regions of galaxies where the disagreement between theory and observation is the greatest. We examine a sample of dwarf galaxies (and one spiral galaxy) from the THINGS high-resolution survey (Walter et al. 2008). We find that the measured rotation curve is quite sensitive to the location of the dynamic center. This …

Dissolution Rates Of Amorphous Al- And Fe-Phosphates And Their Relevance To Phosphate Mobility On Mars, Valerie Tu

UNLV Theses, Dissertations, Professional Papers, and Capstones

Phosphate is an essential element for life on Earth, and therefore if life exists or ever existed on Mars it may have required phosphate. Amorphous Al- and Fe-phosphates rapidly precipitate from acidic solutions and amorphous Al-phosphates likely control phosphate concentrations in some natural waters on Earth. Amorphous phases may be even more important on Mars than on Earth, and amorphous phosphates are therefore likely important in the phosphate cycle on Mars. Despite this importance, however, few dissolution rates exist for amorphous Al- and Fe- phosphates. In this study, dissolution rates of amorphous Al- and Fe-phosphates were measured in flow-through reactors …

Molecular Processes In Astrophysics: Calculations Of H + H2 Excitation, De-Excitation, And Cooling, Matthew Kelley

UNLV Theses, Dissertations, Professional Papers, and Capstones

The implications of H+H2 cooling in astrophysics is important to several applications. One of the most significant and pure applications is its role in cooling in the early universe. Other applications would include molecular dynamics in nebulae and their collapse into stars and astrophysical shocks. Shortly after the big bang, the universe was a hot primordial gas of photons, electrons, and nuclei among other ingredients. By far the most dominant nuclei in the early universe was hydrogen. In fact, in the early universe the matter density was 90 percent hydrogen and only 10 percent helium with small amounts of lithium …

Topics In Galaxy Formation: Pairwise Velocities Of Dark Matter Halos And Molecular Hydrogen Regulated Star Formation In Cosmological Simulations, Robert Jo Thompson

UNLV Theses, Dissertations, Professional Papers, and Capstones

In this dissertation we investigate two distinct challenges within the concordance LCDM model and an unrelated project.

The first is a discrepancy between theory and observation. A massive galaxy sub-cluster known as the `bullet' has fallen through a more massive parent galaxy cluster at a redshift of z=0.296.

Theory finds that in order to reproduce the observational quantities of this cluster, an unusually high relative velocity of v12=3000 km/s between the two cluster's parent halos is required.

We quantify the statistical probability of producing a `bullet-like' halo pair within large N-body simulations, and

conclude that either the LCDM model is …

Parker Winds Revisited: An Extension To Disk Winds, Timothy Waters

UNLV Theses, Dissertations, Professional Papers, and Capstones

A simple 1D dynamical model of thermally driven disk winds is proposed, based on the results of recent, 2.5D axi-symmetric simulations. Our formulation of the disk wind problem is in the spirit of the original Parker (1958) and Bondi (1952) problems, namely we assume an elementary flow configuration consisting of an outflow following pre-defined trajectories in the presence of a central gravitating point mass. Viscosity and heat conduction are neglected. We consider two different streamline geometries, both comprised of straight lines in the (x,z)-plane: (i) streamlines that converge to a geometric point located at (x,z)=(0,-d) and (ii) streamlines that emerge …

New Cross Sections For H On H2 Collisional Transitions, Qianxia Zou

UNLV Theses, Dissertations, Professional Papers, and Capstones

The cross section for H on H₂ collisions is important for astrophysics as well as our understanding of the simple chemical systems. This is the simplest atom-molecule cross section. With a new H₃ potential surface by Mielke et al., we have modified the ABC code by Skouteris, Castillo and Manolopoulos to calculate new cross sections. These cross sections are compared to previous cross section calculations.

Modeling Gamma-Ray Bursts, Amanda Maxham

UNLV Theses, Dissertations, Professional Papers, and Capstones

Discovered serendipitously in the late 1960s, gamma-ray bursts (GRBs) are huge explosions of energy that happen at cosmological distances. They provide a grand physical playground to those who study them, from relativistic effects such as beaming, jets, shocks and blastwaves to radiation mechanisms such as synchrotron radiation to galatic and stellar populations and history. Through the Swift and Fermi space telescopes dedicated to observing GRBs over a wide range of energies(from keV to GeV), combined with accurate pinpointing that allows ground based follow-up observations in the optical, infrared and radio, a rich tapestry of GRB observations has emerged. The general …

A Multi-Wavelength Study On Gamma-Ray Bursts And Their Afterglows, Binbin Zhang

UNLV Theses, Dissertations, Professional Papers, and Capstones

During the prompt emission and afterglow phases, GRBs(Gamma-Ray Bursts) release their huge amount of energy not limited in gamma-ray, but in a wide range of muti-wavelengths, from radio band to GeV gamma-rays. Thanks to the recent missions of Swift and Fermi, I was able to use their multi-wavelength observation data of GRBs and study their physical natures. I have processed all the Swift BAT/XRT and Fermi GBM/LAT GRB observation data. Based on the Swift data, I have studied the following comprehensive topics: (1) high-latitude "curvature effect" of early X-ray tails of GRBs Swift XRT afterglow (2) diverse physical origins of …

Gamma-Ray Burst Populations, Francisco J. Virgili

UNLV Theses, Dissertations, Professional Papers, and Capstones

Over the last fifty years the field of gamma-ray bursts has shown incredible growth, but the amassing of data has also left observers and theorists alike wondering about some of the basic questions surrounding these phenomena. Additionally, these events show remarkable individuality and extrema, ranging in redshift throughout the observable universe and over ten orders of magnitude in energy. This work focuses on analyzing groups of bursts that are different from the general trend and trying to understand whether these bursts are from different intrinsic populations and if so, what can be said about their progenitors. This is achieved through …

Numerical Simulations Of Accretion Disks And Extrasolar Planets, Stefan Luketic

UNLV Theses, Dissertations, Professional Papers, and Capstones

We study mass outflows from astrophysical objects. Using numerical hydrodynamical simulations, we investigate outflows from accretion disks and exoplanets. In the first part of this dissertation, we present the results of Zeus 2D hydrodynamical simulations of the disk photosphere irradiated by strong X–rays that are produced in the innermost part of the disk of an accreting black hole. As expected, the irradiation heats the photosphere and drives a thermal wind. To apply our results to the well– studied X–ray transient source GRO J1655–40, we utilized the observed mass of its black hole and the observed properties of its X–ray radiation …

The Interaction Of Rock And Water During Shock Decompression: A Hybrid Model For Fluidized Ejecta Formation, Audrey Hughes Rager

UNLV Theses, Dissertations, Professional Papers, and Capstones

Crater and ejecta morphology provide insight into the composition and structure of the target material. Martian rampart craters, with their unusual single-layered (SLE), double-layered (DLE), and multi-layered ejecta (MLE), are the subject of particular interest among planetary geologists because these morphologies are thought to result from the presence of water in the target. Also of interest are radial lines extending from the crater rim to the distal rampart of DLE craters. Exactly how these layered ejecta morphologies and radial lines form is not known, but they are generally thought to result from interaction of the ejecta with the atmosphere, subsurface …

Velocity Distribution Of Dark Matter Halos: A Critical Test For The Λ Cold Dark Matter Model, Robert Jo Thompson

UNLV Theses, Dissertations, Professional Papers, and Capstones

The existence of a bullet cluster (such as 1E0657-56) poses a challenge to the concordance cold dark matter model. Here we investigate the velocity distribution of dark matter halo pairs in large N-body simulations with differing box sizes and resolutions. We examine various basic statistics such as halo masses, relative halo velocities, collisional angles, and separation distances in our simulations. We then compare the results to the observational properties of 1E0657-56. Our results suggest that it is very difficult to produce such a halo pair with such a high relative velocity at a redshift of z=0. The relative velocities increase …

Dla-Lbg Cross-Correlation And Basic Properties Of Infrared Galaxies In Cosmological Simulations, Tae Song Lee

UNLV Theses, Dissertations, Professional Papers, and Capstones

PART I

We calculate the cross-correlation function (CCF) between damped Ly-alpha systems (DLAs) and Lyman break galaxies (LBGs) using cosmological hydrodynamic simulations at z = 3. We compute the CCF with two different methods. First, we assume that there is one DLA in each dark matter halo if its DLA cross section is non-zero. In our second approach we weight the pair-count by the DLA cross section of each halo, yielding a cross-section-weighted CCF. We also compute the angular CCF for direct comparison with observations. Finally, we calculate the auto-correlation functions of LBGs and DLAs, and their bias against the …