External Galaxies Commons^™

A Spectrum Of Light: Speculative Poetry Of Celestial Bodies And Astrophysics, Shannon Sosebee

Electronic Theses and Dissertations

This is a collection of speculative poetry with a focus on celestial objects within our solar system and larger bodies outside of our solar system, some of which are only theorized to exist. The author finishes the collection with introspective works, laying bare vulnerabilities and insecurities.

Reconstructing Cosmic Filaments Around Dwarf Galaxies With The Rubin Observatory, Sarah E. Draves, Charlotte Welker, Charlotte Olsen

Publications and Research

The cosmic web is the largest structure in the universe, consisting of streams of gas and dust that connect galaxies made of stars, dark matter, and more gas and dust. Denser areas of the cosmic web tend to have more massive and redder galaxies, which implies a strong connection between cosmic structure and galaxy evolution. The degree to which galaxies are influenced by the cosmic web outside of relatively dense areas, particularly in the case of small filaments near galaxies, is still an area of active study. Low mass galaxies, known as dwarf galaxies, are particularly sensitive to the environment …

A Machine Learning Approach To Discovering Physical Models Of Galaxy Formation, Festa Bucinca

Dissertations, Theses, and Capstone Projects

Galaxies are the breathtakingly beautiful starry islands of the Universe. The process of galaxy formation involves the transformation from simple initial conditions in the early Universe to the complex galaxy structures we observe today. Spanning an immense spatial range and tremendous time scales - from the vastness of the Universe to the scale of individual stars - the physics of galaxy formation is both complex and crucial for understanding the Universe we live in. However, despite significant advancements, our theoretical understanding of galaxy formation remains incomplete.

In the era of big data available from hydrodynamical simulations and observations, Machine Learning …

Active Galactic Nuclei - The Arrhythmic Beat Of A Galactic Heart, Henry James Best V

Dissertations, Theses, and Capstone Projects

Active Galactic Nuclei (AGN) are generally believed to be supermassive black holes (SMBHs) at the center of galaxies which are actively accreting material from the host galaxy. Through this process, they emit radiation across the electromagnetic spectrum both as a smooth continuum and emission lines. However, there is a great variety of the signals we observe–some faint, some bright, some variable and others steady. The wide array of signals produced by AGN is believed to encode both the geometry and the physics surrounding these SMBHs, making them a valuable target for understanding the high gravity limit, their feedback mechanisms to …

Analyzing Hubble Space Telescope Images Of Agn Host Galaxies With Keck Integral Field Spectra, Sebastian Contreras

Physics

In the center of most massive galaxies is a supermassive black hole (SMBH) with a mass that can range from millions to billions of solar masses. It has been observed that more massive SMBHs have a more massive host galaxy bulge, as evidenced by the larger bulge luminosity and stellar velocity dispersion, a correlation known as the BH mass - host-galaxy scaling relation. It suggests a close evolutionary connection between the growth of the SMBH and the growth of its host galaxy. If a SMBH develops an accretion disk to fuel an active galactic nucleus (AGN), it will emit radiation …

The Large-Scale Environments Of Active Galactic Nuclei, Grayson C. Petter

Dartmouth College Ph.D Dissertations

It is now recognized that the energy released by accreting supermassive black holes observed as Active Galactic Nuclei (AGN) is integral in shaping the dynamics of baryons on up to cosmological scales, and AGN thus play a significant role in regulating the formation and evolution of galaxies. Studying the clustering properties of AGN reveals which environments they release this feedback energy into, testing models of AGN-galaxy coevolution and AGN structure. In this thesis, I leverage wide-area photometric and spectroscopic survey data to measure the clustering properties of various AGN samples containing millions of systems, placing tight constraints on the properties …

Investigating The Relationship Between Single And Multiple Sersic Models Of Active Galaxies Using Galfit, Ellie H. Johnson

Physics

Supermassive Black Holes (SMBHs) can be found in the center of almost every galaxy, and in some cases, can form Active Galactic Nuclei (AGNs). AGNs are some of the brightest objects in our observable Universe and are distinguished from quiescent galaxies by accretion onto the central SMBH, which forms a disk where the luminosity is produced. Reverberation mapping (RM) of broad-line AGNs determines the mass of the SMBH by resolving the gravitational sphere of influence of the BH ``in time". In this study, GALFIT is used to fit 2D analytic functions to existing Hubble Space Telescope (HST) images for 23 …

Effect Of Magnetic Draping On Satellite Galaxies In Clusters, Vanessa Brown

Dissertations, Theses, and Capstone Projects

Galaxy evolution has been observed to be influenced by environment. Satellite galaxies orbiting within clusters can experience changes in morphology and composition through various mechanisms such as ram-pressure stripping (RPS), which removes a galaxy’s interstellar medium as it passes through the cluster via direct interaction with the hot intracluster medium gas. An open question is whether intracluster magnetic fields affect galaxy evolution, for example by forming a magnetic layer around infalling galaxies (called magnetic draping) and mitigating gas removal by RPS. Using the code GADGET-3, we compare global properties and mass distributions within identical cluster simulations run with and without …

Examining Galaxy Bulge Regions With The Sloan Digital Sky Survey, Sarah E. Draves, Ariyeh Maller

Publications and Research

Nearly all of the ordinary matter in the universe is located in galaxies, which are made up stars, gas, dust, and black holes, and range in size from a few thousand to a few hundred thousand light years across. Galaxies come in different shapes, but many of them are spiral shaped, and some of those have a central bulge region that is distinct from the rest of the galactic disk. This project used a large data set of galaxies that had their bulge and disk components separated to see what correlations those fractions of each galaxy have with other galaxy …

To The Torus And Beyond: An X-Ray Study Of Agn Tori Morphology, Andrealuna Pizzetti

All Dissertations

Active Galactic Nuclei (AGN) are among the Universe's most energetic and powerful objects, fueled by an accreting supermassive black hole (SMBH) at the host galaxy's center, surrounded by a toroidal structure of dusty gas. Ultraviolet photons arising from the accretion disk get up-scattered to X-rays via inverse Compton scattering by hot electrons close to the accretion disk. Being produced in the very center of the AGN, X-ray photons are powerful messengers that probe the physics of the accretion system and the matter in the surroundings. The torus, formerly considered homogeneous, appears to be a more complex structure of clouds with …

Density And Magnetic Field Asymmetric Kelvin‐Helmholtz Instability, Xuanye Ma, Peter Delamere, Katariina Nykyri, Antonius Otto, Stefan Eriksson, Lihui Chai, Brandon Burkholder, Andrew Dimmock, Yu-Lun Liou, Shiva Kavosi

Publications

The Kelvin‐Helmholtz (KH) instability can transport mass, momentum, magnetic flux, and energy between the magnetosheath and magnetosphere, which plays an important role in the solar‐wind‐ magnetosphere coupling process for different planets. Meanwhile, strong density and magnetic field asymmetry are often present between the magnetosheath (MSH) and magnetosphere (MSP), which could affect the transport processes driven by the KH instability. Our magnetohydrodynamics simulation shows that the KH growth rate is insensitive to the density ratio between the MSP and the MSH in the compressible regime, which is different than the prediction from linear incompressible theory. When the interplanetary magnetic field (IMF) …

Evolution Of Angular Momentum In Triaxial Dark Matter Halos, Tara C. Nester

Honors College Theses

Galactic halos are believed to form through both the early inflow of dark matter from the cosmic web and mergers over an extended period. At the same time, stellar disks are forming within this evolving halo. How a stellar disk responds to a changing halo is investigated in this study using live n-body disks embedded in an analytic triaxial potential. At triaxialities of a few percent, we find that while there are subtle perturbations in the disk, there is no significant change in the total disk angular momentum. However, between 5 and 10% triaxialities there is a sharp transition to …

Exploring The Hot And Gaseous Universe From Infrared To X-Ray, Chamani Gunasekera

Theses and Dissertations--Physics and Astronomy

Over 90% of baryonic matter in the universe exists as astrophysical plasmas. The gas
is often far from thermodynamic equilibrium, so numerical non-equilibrium spectral
synthesis simulations are used to understand observations. cloudy simulates vari-
ous physical conditions, providing spectra predictions. This thesis aims to meet the
challenge of new observatories like the JWST (James Webb Space Telescope) and
XRISM (X-Ray Imaging Spectroscopy Mission). These simulations are no better
than the underlying atomic and molecular database and the fourth chapter details
a long-needed update to an evolving database. The predicted spectra are strongly
affected by the composition of the gas, which …

Hubble Tension And Gravitational Self-Interaction, Corey Sargent, William Clark, Alexander Deur, Balša Terzić

Physics Faculty Publications

One of the most important problems vexing the ΛCDM cosmological model is the Hubble tension. It arises from the fact that measurements of the present value of the Hubble parameter performed with low-redshift quantities, e.g. the Type IA supernova, tend to yield larger values than measurements from quantities originating at high-redshift, e.g. fits of cosmic microwave background radiation. It is becoming likely that the discrepancy, currently standing at 5σ, is not due to systematic errors in the measurements. Here we explore whether the self-interaction of gravitational fields in General Relativity, which are traditionally neglected when studying the evolution …

Molecules In Cool Stars: The A²Π - X²Σ⁺ And The B²Σ⁺ And The B²Σ⁺ - X²Σ⁺ Band Systems Of Cacl, Léo Lavy, Peter F. Bernath

Chemistry & Biochemistry Faculty Publications

Cool red giant stars exhibit absorption bands of calcium monochloride (CaCl) in the optical region. In this work, the bands of CaCl corresponding to the A²Π − X²Σ⁺ transition with v′ ≤ 4 and v″ ≤ 4, and B²Σ⁺ − X²Σ⁺ transition with v′≤ 2 and v″ ≤ 2 are rotationally analyzed with PGOPHER, a multipurpose program for simulating and fitting molecular spectra. All bands were analyzed using high-resolution absorption spectra collected at the National Solar Observatory in 1985, calibrated with atomic lines from a high-resolution emission spectrum obtained …

An Observational Census Of Post-Merger Galaxies And Supermassive Black Hole Pair Evolution, Gregory Walsh

Graduate Theses, Dissertations, and Problem Reports (ETD)

Massive galaxy mergers are a fundamental consequence of the dynamic evolution of the Universe and play a central role in the evolution of galaxies. Because all massive galaxies harbor a central supermassive black hole (SMBH; M ≥ 10⁶ M_⊙), studying these merging systems with electromagnetic (EM) techniques constrains galaxy evolution models and provides a systematic means to examine the astrophysical mechanisms that facilitate the growth of SMBHs. These growing SMBHs are observable across the EM spectrum as Active Galactic Nuclei (AGN). Massive galaxy mergers are a natural formation mechanism for an SMBH pair, eventually evolving into an …