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Item A multi-wavelength study of dwarf galaxies with active massive black holes(Montana State University - Bozeman, College of Letters & Science, 2023) Kimbrell, Seth Jordan; Chairperson, Graduate Committee: Amy E. Reines; This is a manuscript style paper that includes co-authored chapters.Dwarf galaxies which host massive black holes with M less than or equivalent to 106M circled dot give us an opportunity to better understand the formation mechanism behind the supermassive black holes that live in the center of galaxies. Studying how common massive black holes in dwarfs are is an important step in constraining the channels that led to those supermassive black holes. An important part of that study is understanding in what types of dwarf galaxies we can expect to find massive black holes. I present a multi-wavelength study of dwarf galaxies which attempts to find any trends in the morphologies of the hosts of active massive black holes. I begin by modeling the structures of a sample of galaxies which have been identified as black hole hosts; I then perform an identical modeling on a sample of galaxies which show no signs of hosting a massive black hole. I finish by describing an X-ray search for massive black holes among irregular/disturbed galaxies, including the discovery of a very bright X-ray source which is extremely likely to be a massive black hole in a dwarf-dwarf merger. This is one of the first active massive black holes discovered in such a late-stage merger, and it is also notable for radiating at nearly its upper limit.Item A deeper look into X-ray-selected AGN candidates in dwarf galaxies with Chandra(Montana State University - Bozeman, College of Letters & Science, 2023) Sanchez, Adonis Arismendy; Chairperson, Graduate Committee: Amy E. Reines; This is a manuscript style paper that includes co-authored chapters.The ability to accurately discern active massive black holes (BHs) in local dwarf galaxies is paramount to understanding the origins and processes of "seed" BHs in the early universe. We present Chandra X-ray Observatory observations of a sample of three dwarf galaxies (M* < or = 3 x 109 M circled dot, z < or = 0.15) pre-selected by Latimer et al. (2021a) as candidates for hosting active galactic nuclei (AGN). The galaxies were selected from the NASA-Sloan Atlas (NSA) with spatially coincident X-ray detections in the eROSITA Final Equatorial Depth Survey (eFEDS). Our new Chandra data reveal X-ray point sources in two of the three galaxies with luminosities of log(L 2-10keV/[erg s -1]) = 39.1 and 40.4. In the target galaxy with the nondetection, we calculate an upper limit on the luminosity for a potential source. We observed notably higher fluxes and luminosities from the two detected X-ray sources compared to their original eFEDS observations, pointing to possible X-ray variability on the scale of a few years. We plot and fit the spectra of the X-ray sources with a power-law model, finding the likely presence of intrinsic absorption. The X-ray luminosities are above that expected from XRBs, but we cannot definitively rule out stellar-mass compact objects with the data on hand. Assuming the X-ray sources are accreting massive BHs with masses that scale with the stellar mass of the host galaxies, the Eddington ratios are on the order of a few x 10 -3.Item The evolution of the chemical abundance gradients in the merging Magellanic Cloud dwarf galaxies(Montana State University - Bozeman, College of Letters & Science, 2023) Povick, Joshua Tyler; Chairperson, Graduate Committee: David L. Nidever; This is a manuscript style paper that includes co-authored chapters.Dwarf galaxies are some of the most abundant objects in the Universe, but most of them are very distant and very faint. While observing these galaxies does pose some challenges, they are important to study because it is believed that larger galaxies, such as the Milky Way (MW), form from a series of dwarf mergers in a process called hierarchical merging. As if by chance, the Magellanic Clouds (MCs) are both bright enough and close enough to resolve individual stars. These two dwarf satellites of the MW are also in the process of merging together, presenting a great opportunity to examine how the abundance gradients of galaxies are impacted by intergalactic interactions. A great tool to study the MCs is the Apache Point Galactic Evolution Experiment (APOGEE). APOGEE is an H-band near infrared survey commissioned to measure chemical abundances and accurate radial velocities of the MW and its neighborhood. In the MCs, APOGEE was able to observe 6130 red giant branch (RGB) stars in the Large Magellanic Cloud (LMC) and 2062 RGB stars in the Small Magellanic Cloud (SMC). Individual stellar ages are derived using multiband photometry and spectroscopic parameters to compare to stellar isochrones. Using the abundance measurements of 20+ elements and the derived stellar ages, abundance gradients and their evolutions are extracted from radial abundance trends. The stellar ages in the LMC reveal that recent star formation has been concentrated in the center of that galaxy. The fields that overlay a spiral arm in the north of the LMC reveal median ages of ?2 Gyr. The age-metallicity relation (AMR) remains mostly flat with the exception of an increase in overall metallicity ?2 Gyr ago. Looking at the evolution of many abundance gradients in the LMC there is a U-shaped trend with an extremum around the same time as the increase in metallicity. Additionally, the SMC also shows a U-shaped trend in its abundance gradient evolutions albeit a few billion years earlier than the LMC. These results all correspond to a conjectured close interaction between the LMC and SMC in the recent past.Item Black hole scaling relations and feedback in dwarf galaxies(Montana State University - Bozeman, College of Letters & Science, 2022) Schutte, Zachary Willis; Chairperson, Graduate Committee: Amy E. Reines; This is a manuscript style paper that includes co-authored chapters.Over the past decade the discovery of a population of dwarf galaxies which host massive black holes (BH) has prompted the study of how these systems interact, grow and evolve. To address these questions I first present a new relationship between central black hole mass and host galaxy stellar bulge mass extending to the lowest BH masses known in dwarf galaxies (MBH < or ~ 10 5 M circle dot, M* ~ 10 9 M circle dot). I have obtained Hubble Space Telescope imaging of seven dwarf galaxies with optically selected broad-line active galactic nuclei (AGNs) and BH mass estimates from single-epoch spectroscopy. I perform modeling to decompose the structure of these galaxies and find that the majority have an inner bulge/pseudo-bulge component with an exponential disk that dominates the total stellar mass. Using the modeling results, I determine the stellar mass of each photometric component in each galaxy. I determine the M BH - M bulge relation using a total of 12 dwarf galaxies hosting broad-line AGNs, along with a comparison sample of 125 higher-mass galaxies. I find a strong correlation between BH mass and bulge mass which is in good agreement with correlations found previously when only considering higher-mass systems. Second, I investigated the role of AGN feedback in dwarf galaxies by studying Henize 2-10, a dwarf starburst galaxy previously reported to have a central massive black hole. At a distance of ~9 Mpc, it presents an opportunity to resolve the central region and determine if there is evidence for a black hole outflow impacting star formation. I found a ~150 pc long ionized filament connecting the region of the black hole with a site of recent star formation. Spectroscopy reveals a sinusoid-like position-velocity structure that is well described by a simple precessing bipolar outflow. I conclude that this black hole outflow triggered the star formation. The results from the work presented in this thesis show that the coevolution of massive BHs and their host galaxies extends into the lowest mass regime and that AGN feedback plays an important and complex role in dwarf galaxies.Item Searching for signatures of accreting massive black holes in dwarf galaxies(Montana State University - Bozeman, College of Letters & Science, 2022) Latimer, Lilikoi Jean; Chairperson, Graduate Committee: Amy E. Reines; This is a manuscript style paper that includes co-authored chapters.Identifying and analyzing massive black holes (BHs) in dwarf galaxies can advance our understanding of the formation and development of supermassive BHs. Searching for these objects can prove troublesome, however. Massive BHs, with masses of M BH < or ~ 10 6 M circled dot, are smaller than their supermassive cousins (M BH ? 10 6-10 9 M circled dot), and the dwarf galaxies they reside in can yield very different environments than what one might find in a more standard massive galaxy, resulting in a different set of challenges than searching out active galactic nuclei (AGN) powered by supermassive BHs. Here we describe several methods for both identifying AGN candidates powered by massive BHs and searching for evidence to confirm the presence or absence of AGN candidates in dwarf galaxies. For the latter, we use different combinations of radio, X-ray, and mid-IR observations to search for AGN signatures, elucidating the various benefits and difficulties that lie with each one, and reporting the results when applied to our varying samples. For the former, we analyze the efficacy of a mid-IR color-color AGN selection method when applied to dwarf galaxies instead of massive galaxies, and use X-ray observations from a newly-released catalog to search for new AGN candidates in dwarf galaxies.