External Galaxies Commons^™

Measuring Cosmic Expansion From Early To Late Times Using Quasars, Galaxies, & Local Supernovae, Rajeev Vaisakh

Physics Theses and Dissertations

This dissertation investigates the evolution of cosmic expansion across a wide redshift ($z$) range by combining measurements from quasars \& galaxies in the distant universe $(z > 0.8)$ with those obtained from stripped-core collapse supernovae observations from the nearby universe $(z < 0.1)$. Using the DESI spectroscopic survey, we analyze large-scale clustering from quasars over $0.8 < z < 2.1$ and emission line galaxies over $0.8 < z < 1.6$, contributing to DESI DR2 BAO and full-shape measurements of cosmic expansion and structure growth. Combined with BBN in flat $\Lambda$CDM, DESI DR2 BAO gives $H_0 = 68.51 \pm 0.58$ km s$^{-1}$ Mpc$^{-1}$, while combinations of DESI BAO with CMB and supernova data show a preference for evolving dark energy, with representative constraints such as $w_0 = -0.752 \pm 0.057$ and $w_a = -0.86^{+0.23}_{-0.20}$ for DESI+CMB+DESY5. Using the ROTSE-III Supernova Survey and the expanding photosphere method (EPM), we measure distances to a sample of six supernovae for which the thermal phase can be clearly identified. This analysis focuses on testing whether reliable EPM distances can be obtained for this population. The resulting distances will eventually be compared with independent estimates from the literature. Establishing consistency with these external measurements represents an important step toward applying this methodology to larger samples, with the eventual goal of using ROTSE supernova distances to provide an independent measurement of the local Hubble constant.

Active Galaxies In A New Light: The Broad Line Region In The Near-Infrared, Sky O'Donnell

Physics

At the center of most massive galaxies, there is a supermassive black hole with a mass millions to billions of times that of the Sun. In some of these galaxies, so-called Active Galactic Nuclei (AGNs), the supermassive black hole is converting the gas that falls toward it into radiation energy, creating large amounts of luminosity. AGNs are composed of the central supermassive black hole, its accretion disk, and a region just outside, composed of fast-moving ionized gas clouds called the Broad Line Region (BLR). Using spectra obtained with NASA’s Infrared Telescope Facility, we use a technique known as reverberation mapping …

Electromagnetic Counterparts To Active Galactic Nucleus Disk-Embedded Binary Black Hole Mergers, Emily Mcpike

Dissertations, Theses, and Capstone Projects

The accretion disks of active galactic nuclei (AGN) are promising environments for producing binary black hole (BBH) mergers, which have been detected via gravitational waves (GW) with LIGO-Virgo-KAGRA (LVK). BBH mergers embedded in AGN disks are unique among GW formation channels in their generic ability to produce electromagnetic (EM) counterparts, via interactions between the merger remnant and the surrounding disk gas (though these are not always observable). While such mergers represent valuable multi-messenger sources, the lack of predictive statistical models in existing literature currently limits our ability to select possible EM counterparts with GW detections in archival data and in …

Inductive Biases In Field-Level Cosmological Inference From Galaxy Catalogs, James O'Connor Baldwin

Dissertations, Theses, and Capstone Projects

We perform field-level likelihood-free inference of the matter density parameter Ωm from simulated galaxy catalogs using machine learning models with differing inductive biases. Using features extracted from hydrodynamic simulations in the CAMELS suite, we investigate how both observable choice and model architecture govern the extraction of cosmological information. We consider galaxy positions and line-of-sight peculiar velocities, both separately and in combination, and compare permutation-invariant Deep Sets, implemented with either standard multilayer perceptrons (MLPs) or Kolmogorov–Arnold Networks (KANs), to graph neural networks (GNNs) implemented with MLPs, which explicitly encode spatial relations. We evaluate inference performance under both in-distribution and out-of-distribution (OOD) …

A Multi-Frequency Investigation Of Compact Symmetric Objects, Evan E. Sheldahl

Physics & Astronomy ETDs

Some of the brightest objects in the radio sky are jetted active galactic nuclei (AGN), supermassive black holes in the centers of galaxies that accelerate relativistic electrons into twin radio jets. One of the biggest questions surrounding AGN is how they produce radio jets in the first place. We search for an answer to this question by exploring a class of AGN that have uniquely well-constrained physical properties and are thought to be in an early stage of AGN development: compact symmetric objects (CSOs). Throughout our journey with these remarkable sources, we quantify their efficacy as calibrator sources for radio …

X-Raying The Material Surrounding Active Supermassive Black Holes, Isaiah S. Cox

All Dissertations

It is important to understand the nature of the gas and dust immediately surrounding the supermassive black hole (SMBH) in active galactic nuclei (AGN), because this material feeds the accretion disk and couples the activities going on at the AGN scale to the host galaxy. However, there remain large uncertainties on basic properties about this material such as its location and distribution. This is primarily due to the difficulties in resolving spatial information on these scales at extragalactic distances.

AGN emit a tremendous amount of radiation all across the electromagnetic spectrum, including X-rays. The X-rays come from a very small …

Searching For Temporal Variations In The Fine-Structure Constant Using Espresso Spectrograph Data, David Hoffman Iv

Senior Theses

The fine-structure constant α is a dimensionless constant, defined as e²/(4πε₀ℏc) ≈ 1/137. On the order of human timescales, its value is very much unchanging, however, in recent years there has been extensive debate over whether or not the value of α has remained constant over cosmological timescales. With the natural corollary to a changing α being that either one or multiple of its constituent physical constants have also changed in value, observing a variation in the fine-structure constant would have vast ramifications for our understanding of the nature of the early universe and how it has evolved. While past …

Discovery Of Tidal Disruption Event Candidates In The Hubble Catalog Of Variables, Elliot M. Schweitzer

Pitzer Senior Theses

A tidal disruption event (TDE) occurs when a star passes within the tidal radius of the supermassive black hole (SMBH) likely to reside at the center of most galaxies. Within this radius, the star is torn apart as tidal forces overcome the star's binding energy, and roughly half of the stellar debris spirals back towards the SMBH. The formation of an accretion disk produces bright emissions for months to years, modeled to peak in the ultraviolet and extend well into x-ray and optical wavelengths. TDEs occur only about once every 10⁴-10⁵ years per galaxy. As one of …

Numerical Modeling Of Multi-Scale Jet Feedback In Seyfert Galaxies, Julianne Goddard

Theses and Dissertations--Physics and Astronomy

We present a suite of high-resolution cosmological zoom-in simulations investigating the impact of mechanical and thermal feedback from low-luminosity jets launched from supermassive black holes (SMBHs) on Seyfert galaxy evolution from early cosmic times to the present (z ≤ 10). Our models follow the formation of central galaxies within identical dark matter halos of logMhalo/M⊙ ∼ 11.8 at z = 0, seeded with ∼ 10^6M⊙ SMBHs at z ∼ 9.1 and z ∼ 3.7. Feedback from active galactic nuclei (AGN) is implemented in the form of bipolar jets launched along the SMBH spin axis, with jet powers spanning Ljet ∼ …

Active Galactic Nuclei Across Scales: From Blazar Jets To Dark Matter Halos, Stephanie Ann Podjed

Dartmouth College Ph.D Dissertations

Within ΛCDM, galaxies form and evolve within dark matter halos, with both central and satellite galaxies contributing to the total stellar mass content. Virtually every massive galaxy harbors a supermassive black hole (SMBH) at its center, with a small fraction of the population growing by actively accreting material; we call this an active galactic nucleus (AGN). The processes giving rise to an AGN phase (i.e., growth of a SMBH) releases enormous amounts of energy in the form of radiation, outflows, and relativistic jets that are able to significantly affect the formation and evolution of galaxies. Blazars are an extreme class …

Cosmic Duets: A Search For Binary Supermassive Black Holes In Merging Galaxies, Sagar Adhikari

All Dissertations

Galaxies are vast cosmic islands of stars, dust, and gas. They come in various shapes and sizes. They might look static for the timescales we are used to, but they are dynamic and collisional systems that can merge with other galaxies to make bigger galaxies. Most galaxies, including the Milky Way, host a central supermassive black hole (SMBH) with a mass greater than a million (sometimes a billion) times the mass of the Sun. When galaxies merge, their SMBHs form a binary system before ultimately merging. These cosmic duets are of great interest to astronomers and astrophysicists as they are …

Satellite-Host Galaxy Co-Evolution With Next-Generation Regulator Models, Austen Gabrielpillai

Dissertations, Theses, and Capstone Projects

The evolution of satellites galaxies is an unsolved problem in galaxy formation. Recent observations such as the SAGA and ELVES surveys find tension in HI contents and star formation of satellites around their central host galaxies when compared to our own local environment, the Milky Way. These processes are potentially highly influenced by the host's circumgalactic medium (CGM), and to constrain these cases requires accurate and fast modeling of satellites-host interactions. In this work, we present our methodology for evolving z = 0 surviving satellites alongside their central galaxy in sapphire, a CGM regulator co-evolution model of galaxy formation. …

Discovering High-Redshift Bl Lacs And Localizing Grbs For Mev Missions, Yong Sheng

All Dissertations

Blazars are active galactic nuclei (AGNs) with their jets aligned towards Earth. Gamma-ray bursts (GRBs) can be classified into long and short types. Long GRBs are produced by the collapse of massive stars, while short GRBs are formed by binary mergers (neutron star - neutron star or neutron star - black hole mergers). Both objects are the key probes of extreme physics processes and cosmic evolution, providing us an unique window to understand the Universe. My research aims to measure the redshift of blazars and localize GRBs for proposed and upcoming gamma-ray telescopes. BL Lac objects (BL Lacs) are a …

In Search Of Extreme Extragalactic Energy: A Catalog Of Tev-Emitting Bl Lac Candidates From Erosita And Wise, Cassidy M. Metzger, Manel Errando, Andrea Gokus

Senior Honors Papers / Undergraduate Theses

Active galactic nuclei (AGN) are supermassive black holes that reside at galactic centers and are actively accreting matter. In approximately 10% of cases, AGN produce relativistic jets: collimated streams of particles that travel for thousands of light years and have been detected at TeV energies by ground-based gamma-ray observatories. However, the mechanisms that accelerate particles beyond the TeV scale are largely unknown. Currently, only 56 objects are confirmed to accelerate particles to these extreme energies. Here we provide a selection of over 150 sources that exhibit infrared (IR) and X-ray emission profiles similar to those of the 56 TeV sources. …

Probing The 'Mev Gap': Discovery And Characterization Of Persistent And Transient Mev-Gev Gamma-Ray Sources With The Fermi Large Area Telescoope, Scott Joffre

All Dissertations

The MeV Gap is a moniker for the energy regime E~0.1-100 MeV that has lacked sensitive observations for the last 20 years. This is not out of scientific disinterest, but observational challenges. The only instrument currently available to make observations in the MeV Gap is the Fermi Large Area Telescope (LAT). For the first time ever, Fermi-LAT has been leveraged to push its observational capabilities to its absolute lower energy limit to end this 20-year observational gap. Observing the MeV sky is imperative for identifying some of the most luminous galaxies in the Universe known as blazars. The brightest blazars …

A Multidisciplinary Approach To The Thermal And Non-Thermal Mechanisms In Galaxy Clusters, Sheng-Chieh Lin

Theses and Dissertations--Physics and Astronomy

Galaxy clusters form at the intersections of the cosmic web and carry imprints of the structure formation history of the universe. As massive, multi-component systems, they offer unique insights into the astrophysical processes that govern both structure formation and galaxy evolution. Observable across the full electromagnetic spectrum, clusters emit photons through a variety of mechanisms, each tracing different physical processes. This dissertation investigates both the thermodynamic and non-thermal properties of the intracluster medium (ICM) to better understand the physical processes shaping observed phenomena. It comprises three main studies, each targeting a different aspect of galaxy cluster physics. In the second …

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.

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 …

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 …

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 …

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 …

Temporal And Spectral Analysis Of 1es 2344+514 In Two Flaring States Observed By Veritas, Connor Poggemann

Physics

VERITAS observed the bright blazar 1ES 2344+514 during two flaring periods, one from Dec. 17 to Dec. 18, 2015 (MJD 57373-57374) with a peak flux of ~60% of the Crab and another from Nov. 28 to Dec. 3, 2021 (MJD 59546-59551) with a peak flux of ~20% of the Crab. This blazar, located at a redshift of z = 0.044, is classified as an extreme high-frequency-peaked BL Lacertae object (HBL). It is known to be variable, including several previous day-scale flares: Whipple on Dec. 20, 1995, VERITAS on Dec. 7, 2007, and MAGIC on Aug. 11, 2016. The VERITAS near-nightly …

Cosmic Diffuse Neutrino And Gamma-Ray Backgrounds In The Mev Regime, Ilukpitiye Samalka Anandagoda

All Dissertations

Cosmic Multi-Messenger backgrounds include relic diffuse components created in the early Universe and contributions from individual sources. In this dissertation, I present the work done in Anandagoda (2019); Anandagoda et al. (2020, 2023) where type Ia (SNe Ia) and core-collapse supernovae (CCSNe) contributions to the diffuse neutrino and gamma-ray backgrounds in the MeV regime are studied. These backgrounds are referred to as DSNB and DSGB respectively. Based on this work, the diffuse SN Ia background is ~10⁶ times lower (for electron antineutrinos) than the CCSN background making it negligible. The predicted DSNB electron antineutrino flux at earth in the …

Using Deep Neural Networks To Classify Astronomical Images, Andrew D. Macpherson

Honors Projects

As the quantity of astronomical data available continues to exceed the resources available for analysis, recent advances in artificial intelligence encourage the development of automated classification tools. This paper lays out a framework for constructing a deep neural network capable of classifying individual astronomical images by describing techniques to extract and label these objects from large images.