The book Astro4U: An Introduction to the Science of the Cosmos excites students about the grandeur of astronomy and how the universe functions. Filled with vibrant figures and informative tables that support the written text, the book has a fresh, casual, student-friendly tone that dramatically increases interest in the material while also making it more accessible.The book provides a college-level description of science, with astronomy serving as the vehicle of delivery for displaying the scientific model. The content follows a traditional progression, beginning with a study of the sky, followed by discussions of ancient and medieval astronomy, modern scientific practices, and key physical principles. Chapters move through the Solar System, stars, then galaxies, and finally the cosmos as a whole. The book presents astronomy as the story of light and gravity, crucial threads that run through the text. Chapters include Ponder Sections—in-depth, quantitative passages dealing with particular applications of interest such as “space junk”, the solar energy budget, and light travel time. Appendices provide information about physical constants, astronomical symbols, and multiple choice problem sets.Because students often express concern about the math content in astronomy classes, the book begins with a chapter entitled “Astro Maths” that reviews all the mathematical skills and concepts needed to complete the course. This up-front investment increases student confidence, eliminates one of the primary blocks students face, and improves chances for student achievement and success.Astro4U is written for general education survey courses in astronomy that are geared toward non-science majors. / https://dc.etsu.edu/etsu_books/1188/thumbnail.jpg

In this dissertation, we investigate various aspects of dark matter detection and model building. Motivated by the cosmic ray positron excess observed by PAMELA, we construct models of decaying dark matter to explain the excess. Specifically we present an explicit, TeV-scale model of decaying dark matter in which the approximate stability of the dark matter candidate is a consequence of a global symmetry that is broken only by instanton-induced operators generated by a non-Abelian dark gauge group. Alternatively, the decaying operator can arise as a Planck suppressed correction in a model with an Abelian discrete symmetry and vector-like states at an intermediate scale that are responsible for generating lepton Yukawa couplings. A flavor-nonconserving dark matter decay is also considered in the case of fermionic dark matter. Assuming a general Dirac structure for the four-fermion contact interactions of interest, the cosmic-ray electron and positron spectra were studied. We show that good fits to the current data can be obtained for both charged-lepton-flavor-conserving and flavor-violating decay channels. Motivated by a possible excess of gamma rays in the galactic center, we constructed a supersymmetric leptophilic higgs model to explain the excess. Finally, we consider an improvement on dark matter collider searches using the Razor analysis, which was originally utilized for supersymmetry searches by the CMS collaboration.

A study of magnetohydrodynamics (MHD) in an open universe is presented. We discuss the data and justification behind our choice of an open universe for investigation in this thesis, as opposed to the closed universe theory, which is more appealing in some ways. We explicitly define all parameters used in the analysis of magnetohydrodynamic Bianchi Type V cosmologies and outline the formulation behind them. We then proceed to present a solution to a Bianchi Type V magnetohydrodynamic cosmology with a diagonal metric. After that, the results are compared with present observations. Lastly, we conclude with an assessment of the model and discuss areas for future work, such as nondiagonal metrics and the role of perturbations of the models in galaxy formation.

<p> Stellar velocity dispersion is a key measurable quantity in galactic astronomy, yet its variation during galaxy mergers is not well-understood theoretically. Thus, while it is fairly common to measure velocity dispersion in galaxies that are in the process of merging, it is unclear how these measurements should be interpreted. In this dissertation, I provide a theoretical analysis of the evolution of stellar velocity dispersion during galaxy mergers. This is done using a set of numerical simulations. The temporal and directional evolution of velocity dispersion are examined in detail for a variety of merger simulations. I also examine the effects that dust attenuation and star formation have on measurements of velocity dispersion by creating detailed, Doppler broadened galaxy spectra. Velocity dispersions are measured from the synthetic spectra using the same technique that is employed for observations of real galaxies. </p><p> I find that velocity dispersion increases rapidly and significantly as two galaxies pass through one another. As galaxies recede from a collision, their velocity dispersions rapidly decrease and nearly return to their pre-collision values. Velocity dispersion increases in all directions during collisions, however the enhancement is most significant along the collision axis. After the nuclei of the progenitor system coalesce, the velocity dispersion oscillates slightly of the coalesced system oscillated around its final equilibrium value for up to several dynamical timescales. </p><p> I also find that the mean velocity dispersion of young stars tends to be lower than the velocity dispersion of the galaxy as a whole. The young stars become dynamically heated with time. In most cases, the youngest stars are found in dusty environments. Thus, dust preferen- tially obscures young stars, partially removing them from the flux-weighted velocity dispersion measurement. This causes flux-weighted velocity dispersion measurements to be elevated with respect to mass-weighted measurements because the young stars are dynamically cooler. On the other hand, since young stellar populations are brighter, per unit mass, than older stellar populations, the low dispersion of young stars tends to weight measurements of velocity dis- persion downward when the young stars are not more significantly obscured by dust than the older populations.</p>

<p>Kuiper Belt Objects (KBOs) are primordial icy objects in the outer solar system. Compositional information for KBOs helps us understand the original environment of the solar system as well as identify objects that are compositionally anomalous. Due to the faint nature of KBOs, very few spectroscopic observations have been made of them. Instead, photometric observations at infrared wavelengths are made to partially construct their spectra. I calculate near infrared reflectances for 12 objects using photometric observations from the Gemini North telescope. I combine these near infrared reflectances with data from the Spitzer Space Telescope. This combination of Gemini and Spitzer photometry along with compositional model analysis allows us to find the surface composition (organics, <i> H</i>₂<i>O</i>, <i>CO</i>₂, <i> CH</i>₄, and other hydrated silicates) for these 12 objects. I found that my objects fit into one of four taxonomic classes found in the Kuiper Belt. We have found using the color analysis, that Haumea has water on its surface and Eris is most likely to have methane on its surface. By analyzing this data we measure the compositional mixing in the outer solar system. </p>

<p>In my thesis I investigate the luminous <i>z</i> &sim; 3 Lyman break galaxies in deep wide field surveys.</p><p> In the first part of the thesis, I use the LBT/LUCIFER to observe a lensed high-redshift star-forming galaxy (J0900+2234) at <i>z</i> = 2.03. With the high S/N near-IR spectroscopic observations, I reveal the detailed physical properties of this high-redshift galaxy, including SFR, metallicity, dust extinction, dynamical mass, and electron number density.</p><p> In the second part of the thesis, I select a large sample of LBGs at <i> z</i> &sim; 3 from our new LBT Bo&ouml;tes field survey, and study the bright end luminosity function (LF), stellar mass function (SMF) and clustering properties of bright LBGs (1<i>L</i>_&lowast; &lt; <i> L</i> &lt; 2.5<i>L</i>_&lowast;). Together with other LF and SMF measurements, the evolution of LF and SMF can be well described by continuously rising star formation history model. Using the clustering measurements in this work and other works, a tight relation between the average host galaxy halo mass and the galaxy star formation rate is found, which can be interpreted as arising from cold flow accretion. The relation also suggests that the cosmic star formation efficiency is about 5%-20% of the total cold flow mass. This cosmic star formation efficiency does not evolve with redshift (from <i>z</i> &sim; 5 to <i>z</i> &sim; 3), hosting dark matter halo mass (10¹¹ &ndash; 10¹³ [special characters omitted]), or galaxy luminosity (from 0.3<i>L*</i> to 3<i>L* </i>).</p><p> In the third and fourth parts, with the spectroscopic follow-up observations of the bright LBGs, I establish a sample of spectroscopically-confirmed ultraluminous LBGs (ULBGs) in NOAO Boo&Dot;tes field. With this new ULBG sample, the rest-frame UV LF of LBG at M_1700&angst; = &minus;23.0 was measured for the first time. I find that the ULBGs have larger outflow velocity, broader Ly&alpha; emission and ISM absorption line profiles, and more prominent C <p style="font-variant: small-caps">IV </p> P-Cygni profile. This profile may imply a top-heavy IMF in these ULBGs. The ULBGs have larger stellar mass and SFR, but smaller dust extinction than the typical <i>L*</i> LBGs at <i>z</i> &sim; 2 &ndash; 3. We proposed two evolutionary scenarios, pre-burst and post-burst. The properties of the ULBGs, especially the morphologies, prefer the pre-starburst scenario. Further high spatial resolution HST imaging and IFU spectroscopic observations will allow us to distinguish these two scenarios.</p>

<p> The Arecibo Legacy Fast ALFA (ALFALFA) survey is a blind, extragalactic survey in the 21cm emission line of atomic hydrogen (HI). Presently, sources have been cataloged over &ap;4,000 deg² of sky (~60% of its final area), resulting in the largest HI-selected sample to date. We use the rich ALFALFA dataset to measure the statistical properties of HI-bearing galaxies, such as their mass distribution and clustering characteristics. These statistical distributions are determined by the properties of darkmatter on galactic scales, and by the complex baryonic processes through which galaxies form over cosmic time. As a result, detailed studies of these distributions can lead to important insights in galaxy formation &amp; evolution and near-field cosmology.</p><p> In particular, we measure the space density of HI-bearing galaxies as a function of the width of their HI profile (i.e. the velocity width function of galaxies), and find substantial disagreement with the distribution expected in a lambda cold dark matter (&Lambda;CDM) universe. In particular, the number of galaxies with maximum rotational velocities &upsi;<i>_rot</i> &ap; 35 kms^&ndash;1 (as judged by their HI velocity width) is about an order of magnitude lower than what predicted based on populating &Lambda;CDM halos with modeled galaxies. We identify two possible solutions to the discrepancy: First, an alternative dark matter scenario in which the formation of low-mass halos is heavily suppressed (e.g. a warm dark matter universe with keV-scale dark matter particles). Secondly, we consider the possibility that rotational velocitites of dwarf galaxies derived from HI velocity widths may systematically underestimate the true mass of the host halo, due to the shape of their rotation curves. In this latter scenario, quantitative predictions for the internal kinematics of dwarf galaxies can be made, which can be checked in the future to probe the nature of dark matter.</p><p> Furthermore, we take advantage of the overlap of ALFALFA with the Sloan Digital Sky Survey (SDSS), to measure the number density of galaxies as a function of their &ldquo;baryonic&rdquo; mass (stars + atomic gas). In the context of a &Lambda;CDM cosmological model, the measured distribution reveals that low-mass halos are heavily &ldquo;baryon depleted&rdquo;, i.e. their baryonic-to-dark mass ratio is much lower than the cosmological value. These baryon deficits are usually attributed to stellar feedback (e.g. supernova-driven gas outflows), but the efficiency implied by our measurement is extremely high. Whether such efficient feedback can be accommodated in a consistent picture of galaxy formation is an open question, and remains one of the principle scientific drivers for hydrodynamic simulations of galaxy formation.</p><p> Lastly, we measure the clustering properties of HI-selected samples, through the two-point correlation function of ALFALFA galaxies. We find no compelling evidence for a dependence of clustering on HI mass, suggesting that the relationship between galactic gas mass and host halo mass is not tight. We furthermore find that HI galaxies cluster more weakly than optically selected ones, when no color selection is applied. However, SDSS galaxies with blue colors have very similar clustering characteristics with ALFALFA galaxies, both in real as well as in redshift space. On the other hand, HI galaxies cluster much more weakly than optical galaxies with red colors, and in fact &ldquo;avoid&rdquo; being located within &ap;3 Mpc from the latter. By considering the clustering properties of &Lambda;CDM halos, we confirm our previous intuition for an <i>M_HI-M_h</i> relation with large scatter, and find that spin parameter may be a key halo property related to the gas content of present-day galaxies.</p>

Stars with masses roughly less than half a solar mass, M stars, constitute 75% of all stars in the Galaxy. However, due to their enigmatic nature, it remains difficult to measure these stars' physical properties. This project performs such characterization through the investigation of eclipsing binary star systems. By utilizing precise photometric data from NASA's Kepler Mission, we present this study on all M star eclipsing binaries in the Kepler dataset. We modeled our selected targets' light curves using existing code and vetted our sample for prime candidates for radial velocity follow up. Using available time on various telescopes, we obtained radial velocity measurements and are able to determine the effective temperatures of our target sample; a proposal has been submitted for further study with these and other observatories. With this information an absolute mass scale for the eclipsing systems allows us to fully characterize the individual stars in terms of their mass, radius, and temperature, leading us to derived luminosities. Ultimately, we hope to fill the current knowledge gap that concerns this dominant class of planet formation in the galaxy.

<p> I use N-body simulations of the Milky Way and its satellite population of dwarf galaxies to probe the small-scale power spectrum and the properties of the unknown dark matter particle. The number of dark matter satellites decreases with decreasing mass of the dark matter particle. Assuming that the number of dark matter satellites exceeds or equals the number of observed satellites of the Milky Way, I derive a lower limit on the dark matter particle mass of <i>m_WDM</i> > 2.1 keV for a thermal dark matter particle, with 95% confidence. The recent discovery of many new dark matter dominated satellites of the Milky Way in the Sloan Digital Sky Survey allows me to set a limit comparable to constraints from the complementary methods of Lyman-&alpha; forest modeling and X-ray observations of the unresolved cosmic X-ray background and of halos from dwarf galaxy to cluster scales. </p><p> I also investigate the claim that the largest subhalos in high resolution dissipationless cold dark matter (CDM) simulations of the Milky Way are dynamically inconsistent with observations of its most luminous satellites. I quantify the effects of the adopted cosmological parameters on the satellite densities and show the tension between observations and simulations adopting parameters consistent with WMAP9 is greatly diminished. I explore warm dark matter (WDM) cosmologies for 1-4 keV thermal relics. In 1 keV cosmologies subhalos have circular velocities at kpc scales 60% lower than their CDM counterparts, but are reduced by only 10% in 4 keV cosmologies. Recent reports of a detected X-ray line in emission from galaxy clusters has been argued as evidence of sterile neutrinos with properties similar to a 2 keV thermal relic. If confirmed, my simulations show they would naturally reconcile the densities of the brightest satellites and be consistent with the abundance of ultra-faint dwarfs. </p><p> I conclude by using N-body simulations of a large set of dark matter halos in different CDM and WDM cosmologies to demonstrate that the spherically averaged density profile of dark matter halos has a shape that depends on the power spectrum of initial conditions. Virialization isotropizes the velocity dispersion in the inner regions of the halo but does not erase the memory of the initial conditions in phase space. I confirm that the slope of the inner density profile in CDM cosmologies depends on the halo mass with more massive halos exhibiting steeper profiles. My simulations support analytic models of halo structure that include angular momentum and argue against a universal form for the density profile.</p>

<p> In this work, we determine heating rates in reconnection formed flare loops with analysis of observations and models. We utilize the spatially resolved ultraviolet (UV) light curves and the thick-target hard X-ray (HXR) emission to construct heating rates of a few thousand flare loops anchored at the UV footpoints. These loops are formed and heated by magnetic reconnection taking place successively. These heating rates are then used as an energy input in the zero-dimensional Enthalpy-Based Thermal Evolution of Loops (EBTEL) model to calculate the evolution of plasmas in these loops and compute synthetic spectra and light curves in Soft X-ray (SXR) and extreme ultraviolet (EUV), which compare favorably with those observed by the <i> Geostationary Operational Environmental Satellite (GOES),</i> <i> Reuven Ramaty High Energy Solar Spectroscopic Imager (RHESSI)</i>, and <i> Solar Dynamics Observatory (SDO).</i> With a steady-state assumption, we also compute the transition-region differential emission measure (DEM) at the base of each flare loop during its decay phase, and compare the predicted UV and EUV emissions at the footpoints with AIA observations. This study presents a method to constrain heating of reconnection-formed flare loops using all available observations, and provides insight into the physics of energy release and plasma heating during the flare. Furthermore, using <i> RHESSI</i> HXR observations, we could also infer the fraction of non-thermal beam heating in the total heating rate of flare loops. For an M8.0 flare on 2005 May 13, the lower limit of the total energy used to heat the flare loops is estimated to be 1.22&times;10³¹ ergs, out of which, less than 20% is carried by beam-driven upflows during the impulsive phase. The method is also applied to analyzing an eruptive M3.7 flare on 2011 March 7 and a compact C3.9 flare on 2012 June 17. Both flares are observed in EUV wavelengths by the Atmospheric Imaging Assembly (AIA) and Extreme Ultraviolet Variability Experiment (EVE) onboard the <i>SDO,</i> which allow us to investigate the flare evolution from the heating to cooling phase. The results show that the model-computed synthetic EUV emissions agree very well with those observed in AIA bands or EVE lines, indicating that the method successfully captures heating events and appropriately describes mean properties of flare plasma shortly after the heating phase.</p>