Massive young stars dynamically modify their surroundings, altering their stellar nurseries and the gas that exists between stars. With my research, I assess the modification of the Galactic magnetic field within HII regions and stellar bubbles associated with OB stars. Because HII regions are plasmas, magnetic fields should be important to the dynamics of the region. Understanding how the magnetic field is modified in these structures is critical for inputs to simulations and for assessing stellar feedback. To obtain information on the properties of the magnetic field, I measure the Faraday rotation of linearly polarized radio waves that pass through the plasma of the HII region. In this thesis, I present results of Faraday rotation studies of two Galactic \HII regions. The first is the Rosette Nebula (l = 206 deg, b = -1.2 deg), and the second is IC 1805 (l = 135 deg, b = 0.9 deg), which is associated with the W4 Superbubble. I measure positive rotation measure (RM) values in excess of +40 to +1200 rad m^-2 due to the shell of the Rosette nebula and a background RM of +147 rad m^-2 due to the general interstellar medium in this area of the Galactic plane. In the area of IC 1805, I measure negative RM values between +600 and --800 rad m^-2 due to the HII region. The sign of the RM across each HII region is consistent with the expected polarity of the large-scale Galactic magnetic field that follows the Perseus spiral arm in the clockwise direction, as suggested by Van Eck et al. (2011, ApJ, 728, 14). I find that the Rosette Nebula and IC 1805 constitute a "Faraday rotation anomaly", or a region of increased RM relative to the general Galactic background value. Although the RM observed on lines of sight through the region vary substantially, the |RM| due to the nebula is commonly 100 -- 1000 rad m^-2. In spite of this, the observed RMs are not as large as simple, analytic models of magnetic field amplification in HII regions (such as by magnetic flux conservation in a swept-up shell) might indicate. This suggests that the Galactic field is not increased by a substantial factor within the ionized gas in an HII region. Finally, these results show intriguing indications that some of the largest values of |RM| occur for lines of sight that pass outside the fully ionized shell of the IC 1805 HII region, but pass through the Photodissociation Region (PDR) associated with IC 1805.

The Bok globule B335 is a small molecular cloud in the solar neighbourhood near the galactic plane. The aim for this three-paper-study is to construct and analyze the extinction for this globule. The method we apply is to use the light from field stars behind the cloud in broadband filters ranging from UV to the mid-infrared. We have observations performed at the ESO telescopes at La Silla and Paranal as well as at the Nordic 2.5 m telescope at La Palma. Together with images and spectra from 2MASS-, ISO- and Spitzer-archives we are able to cover the wavelength range from 0.35 to 24 μm. An important tool to analyze these observations results in order to get the extinction is the grid of synthetic stellar atmospheric spectra provided by Hauschildt (2005). The extinction so received is a result in itself. From the analysis of the extinction wavelength dependence we derive properties of the dust, especially its composition and grain size distribution. By modeling the grain size distribution we are able to find the extinction from the reddening of the stars. We find that the extinction in the optical wavelength 0.35 to 2 μm range nicely follows the functional form described by Cardelli et al. (1989). Our result from the wavelength range redward of 2 μm show an extinction dependent on the part of the cloud examined. For the rim of the cloud we get an extinction similar to that reported earlier for the diffuse interstellar medium. From the central parts of the cloud, however, a higher extinction was found. Our grain size model contains a carbonaceous particle distribution and a silicate one. The result can be explained by depletion of carbon onto carbonaceous grains and also by carbon onto all grains including the silicates. Our modeling of the extinction and our classification of the background stars allow us to - determine the distance to the globule - estimate the gas column density ratio - estimate the mass of globule - get a handle on the dust conversion processes through the grain size distribution   From the water- and CO-ice spectra we are able to estimate the ice column densities. We find similar ice column densities for the two ices. The estimates differ, when calculated from band strengths or from Lorenz-Mie calculations of ice mantles on the grain size distribution, by a factor of two.

Thesis (Ph.D.) - University of Buenos Aires, 2005. / PDF copy of thesis. Includes bibliographic references.

In this thesis I investigate three key questions about the interstellar medium (ISM) and star formation in nearby galaxies. The first question is, “how do bars and galaxy interactions affect the distribution of cold gas and the level of central star formation in galaxies?” I use publicly-available spatially-resolved images of CO(1-0) emission in a sample of 126 nearby galaxies from the Extragalactic Database for Galaxy Evolution (EDGE) survey to measure molecular gas concentrations, and I use spatially-resolved optical spectroscopy from the Calar Alto Legacy Integral Field Area (CALIFA) survey to measure the level of central star formation enhancement. I find that gas concentration and the level of central star formation enhancement are positively correlated in barred galaxies but not in unbarred galaxies, and that interacting galaxies show signs of a correlation but not in all cases. These results indicate that central star formation enhancement occurs only in barred galaxies and interacting galaxies with high gas concentrations, which supports theories of bar- and interaction-driven galaxy evolution. The second question is, “what is the relationship between mid-infrared (MIR) emission and molecular gas at spatially-resolved scales in galaxies?” I extend previous work, which found a tight correlation between global MIR emission in the Wide-field Infrared Survey Explorer (WISE) 12 micron band and CO emission from single-dish radio telescopes, to spatially-resolved scales using EDGE CO data smoothed to WISE 12 micron resolution. I find that these quantities are tightly correlated at ~kiloparsec scales, and that the correlation shows offsets from galaxy to galaxy. I find that these offsets are explained best by differences in the level of global near- and far-ultraviolet emission, and that the 12 micron-CO correlation is the strongest of all the resolved correlations that I considered. These results suggest that there is a tight physical link between WISE 12 micron emission and CO emission on kiloparsec scales, possibly due to a connection between polycyclic aromatic hydrocarbons (PAHs, which dominate the 12 micron emission) and molecular gas. My findings can be used to estimate resolved CO emission based on (easily obtained) WISE 12 micron images and a small number of global multi-wavelength measurements. These results also motivate further work exploring the CO-PAH connection in more diverse conditions and at higher resolution. Finally, the third question is, “what is the ISM content of red star-forming galaxies?” In comparison to blue star-forming galaxies (“blue actives”) which lie on or above the star-forming main sequence (SFMS), these “red misfits” tend to lie on or slightly below the SFMS. I find that the main property other than colour that differentiates red misfits from blue actives is their low gas mass fractions. The gas depletion times and gas-to-dust ratios are similar between these populations. My results indicate that the star formation of red misfits is in the act of quenching. The unifying theme of each of these projects is the approach: studying key questions in nearby galaxies based on their molecular gas content along with other multi-wavelength data, at a variety of resolutions. This approach is enabled by large publicly available multi-wavelength data sets at a variety of physical resolutions. Surveys of the global gas content of galaxies with accompanying multi-wavelength data will always be larger, and will continue to be an important reference for smaller resolved surveys. I hope that this thesis serves as a useful comparison between the science that can be done on both global and resolved scales, and will motivate future work on the connection between the ISM and star formation in nearby galaxies. / Thesis / Doctor of Science (PhD)

Every scientific experiment or innovation goes through a phase of testing equipment. This is not only true for experiments in the laboratory, but also very relevant for experiments on other planetary bodies. In order to test tools and robotic equipment that are destined for another planet, moon, asteroid or comet, it is necessary to simulate the regolith environment on that surface. In this thesis we have provided an overview of two methods for regolith simulant development. In one approach we made simulants in different compositions to find the best spectral fit to Jupiter Trojan asteroids. At visible to near-infrared (VNIR) wavelengths, the Trojans' spectra have low overall reflectance and red spectral slopes, and a distinctive 10 μm plateau at thermal infrared (TIR) wavelengths. Trojan spectra may be explained by high porosity, fine particulate silicate minerals like olivine mixed with opaques and organics. Our Trojan simulants were made from silicate (olivine), opaque (iron sulfide) and organics (coals) in various proportions and particle sizes. Resulting mixtures were analyzed with spectrometers VNIR to TIR wavelengths. While the perfect Trojan simulant was not created, compositional and particle size effects were characterized, which helps to better understand the Trojan spectra. It is unknown how water ice content changes regolith and dust properties. To be safe during lunar exploration more research and modeling of possible regolith behavior is necessary. The second project presented in this thesis is about a new production method for lunar permanently shadowed regions (PSRs) icy regolith simulant. We build on an existing lunar highlands simulant, by adapting it for lunar poles, where water ice might be present in permanently shadowed regions. We have developed a production pipeline to make granular icy simulant with variable water ice content. We found that icy simulant has an increased porosity, that persists even after dehydration.

Binary asteroid systems make up roughly 15% of objects occupying near-Earth space, the Main Belt, and trans-Neptunian space. The impact history of asteroids in binary systems represents an interesting aspect of the general problem pertaining to the nature and evolution of surfaces for such objects. Specifically, the post-impact dynamics of ejecta and its relation to surface modification is a challenging question owing, in part, to the unusual gravitational field in a binary system and the subsequent capture and emplacement of debris on either binary component. Observable differences or similarities between the two bodies in the color, reflectance, thermal properties, and grain properties of their respective regoliths could give insight into the system's past and the circumstances of recent impacts. Here we present simulations of impact scenarios in a wide variety of binary systems in order to generate a large family of prediction models for resurfacing and ejecta covering outcomes due to impacts. In this way, we can address our main science question of how specific binary system parameters influence the evolution of their surfaces. To create a library of ejecta outcomes, we first developed the Rebound Ejecta Dynamics (RED) package (Larson and Sarid 2021), an N-body integrator designed to model post-impact debris dynamics that builds on the existing Rebound software (Rein and Tamayo 2015). This package allows us to vary the many of the important parameters of a binary system, including primary-secondary separation, rotation periods, and mass ratios, as well as impact-related parameters, such as impact surface location, ejecta size and velocity distribution, and ejecta compositions. Our simulations generally use 10,000 particles and cover one week of simulation time. From our simulations, we calculate the percentage of the system that is resurfaced, the distance that particles travel from the impact site, and the percentage of particles that impact the surface. These regions of resurfacing can often be observed with different colors or spectral properties than the original surface. We find that there are trends in ejecta end-states as a function of binary system properties (i.e., primary rotation period and system mass ratio) for several common impact scenarios. We analyzed the dominant effect that influences the outcome of each impact event.

In this dissertation work we sought to answer questions about the age, composition, and origin of planetary bodies. We implemented multiple approaches to answer these questions. To determine the age of the Clarissa asteroid family we implemented a modified version of SWIFT: a Solar System integration software package by Levison & Duncan (1994) to account for gravitational as well as thermal perturbations. This work constrained the age of the Clarissa asteroid family to be 56 ± 6 My. Next, we used a sum to one constraint weighted least squares (STO WLS) modeling approach to model thermal infrared (TIR) spectra of a suite of primitive asteroid analogs spectrally and volumetrically dominated by fine particulates ( < 38 µm). We determined that an alternative approach to the STO WLS model is needed to analyze asteroid regolith when it is dominated by fine particles ( < 90 µm). Our next approach included the Trojan asteroids (911) Agamemnon, (1172) Aneas, and (624) Hektor, and primitive asteroid (944) Hidalgo whose emissivity spectra share a prominent 10 µm plateau that is also present in cometary comae spectra. We used Multiple Sphere T-Matrix (MSTM) and Hapke reflectance models to model the asteroid spectral features using a mixture of olivine components (Mg-rich and Fe-rich olivine), fine particles (~0.5-1.0 µm), and lunar-like porosities (~74-87%). Finally, we used a light scattering Mie and Monte Carlo radiative transfer approach to model ambient (measured under Earth-like conditions) lunar regolith spectra. This study indicates that additional work needs to be done to develop an integrated thermal and light-scattering model that can replicate the effects of the thermal gradient present under lunar environment conditions because a light-scattering model alone is not able to reproduce the observed changes in the spectra that we see with space weathering.

Transiting exoplanets provide the best opportunity for planetary characterization, and thus the search for life outside the Solar System. These planets orbit such that they pass in front ("transit'') and behind ("eclipse'') their host star, and a spectrum of the lost flux constrains the atmospheric properties of the planet. In transits, the flux modulation scales with the cross-sectional area of the planet, and the spectrum includes signatures of molecules in the upper atmosphere of the planet's terminator, which the host star's light passes through on the way to the observer. With eclipses, the lost flux is the direct emission of the planet, a spectrum of which contains emission and absorption features of molecules in the atmosphere depending on atmospheric thermal structure. These signals scale with the size and brightness of the planet and are so dwarfed by the brightness of the host star that only > 1000 K Jupiter-sized planets are observable with current instrumentation. In this work, I develop new techniques and compare existing data analysis methods to extract weak planetary signals. Chapter 2 describes a new elliptical photometry data analysis approach to disentangle exoplanet observations from telescope vibrations. Chapter 3 describes an analysis of Spitzer Space Telescope observations of eclipses of the planet WASP-29b using elliptical photometry and two different light curve modeling methods, and addresses the differences between results. In Chapter 4, I analyze two similar observations of WASP-34b using a grazing eclipse light-curve model. Finally, in Chapter 5 I reanalyze all Spitzer eclipse observations of the Neptune-sized GJ 436b, applying the lessons learned from my earlier works, and comparing my results with the literature.

Star formation is an inherently multi-scale process, connecting scales from the kiloparsecs of the galactic disk to the single AU scale of a protostar. In the middle of these scales are star clusters and molecular clouds, the structures in which most stars form. The clouds and clusters are connected via the interstellar medium, the gas and dust making up the matter between stars. In the cold phases of this medium rests the first steps of star formation, the formation of molecular gas and networks of filaments. This cold, neutral medium (CNM) hosts a handful of physical mechanisms, all contributing to the structures that feeds star formation. In this thesis work, we present a suite of simulations using the magneto-hydrodynamical code Ramses to investigate the role of turbulence, magnetic fields and cooling on the formation of filaments and clusters in the CNM. Through 9 different models we find that velocity dispersions in the CNM play a significant role in the formation of structure, requiring a balance between turbulence, self gravity and cooling to form filaments. We find magnetic fields, initialized at strengths of 7 muG, affect the formation of filaments, creating higher percentages of star-forming dense gas and lower percentages of molecular gas. Both magnetic fields and velocity dispersion in the gas affect the formation rate of clusters early in the simulation. Our 8 km/s simulations present a good initial condition for star formation that can include multiple scales of the process and recreate accurate clouds and filamentary structure. / Thesis / Master of Science (MSc)

The Almahata Sitta meteorites produced from the breakup of 2008 TC3 were highly unusual, as the stones contained various meteorite types, with stones spanning almost every meteorite petrologic type. This was considered a remarkable event at the time since meteorites of different types had never been found among the same fall before. However, new discoveries of exogenous material on (4) Vesta, (101955) Bennu, and (162173) Ryugu in subsequent years imply that this event may be more common than initially thought. This is unexpected due to the high average collisional velocity in the asteroid belt of ~5 km/s. High velocity impacts are more likely to have low impact retention efficiencies, which lowers the likelihood of xenoliths surviving the collision. Our understanding of this material and the mechanisms by which it is delivered can give insights into the dynamic histories of these asteroids and even the greater dynamic history of the asteroid belt.