Thesis (Ph.D.)--York University, 2005. Graduate Programme in Chemistry. / Typescript. Includes bibliographical references. Also available on the Internet. MODE OF ACCESS via web browser by entering the following URL: http://proquest.umi.com/pqdweb?index=0&did=1163224921&SrchMode=1&sid=7&Fmt=2&VInst=PROD&VType=PQD&RQT=309&VName=PQD&TS=1195066319&clientId=5220

Thesis (Ph. D.)--University of Wisconsin--Madison, 1975. / Typescript. Vita. eContent provider-neutral record in process. Description based on print version record. Includes bibliographical references.

Thesis (Ph. D.)--University of Chicago, Dept. of Astronomy and Astrophysics, March 2000. / Includes bibliographical references. Also available on the Internet.

Thesis (Ph. D.)--University of Chicago, Dept. of Astronomy and Astrophysics, August 1997. / Includes bibliographical references. Also available on the Internet.

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

The formation of stars from interstellar gas is the cornerstone of galaxy evolution. This thesis represents work undertaken in order to characterise the role of cool interstellar gas, and its relation to star formation, in galaxy evolution across cosmic time. In particular, it concentrates on star forming galaxies at the extremes of the galaxy assembly spectrum - extremely faint dwarfs, and extremely luminous starbursts - in an attempt to test the limits of galaxy evolution models. The thesis falls into two complimentary halves, addressing topics in the low redshift and high redshift Universe respectively. In the low redshift Universe, I discuss multi-wavelength studies of large samples of z rv O galaxies, which include extremely faint dwarf galaxies in the Local Volume. Using these samples, it is possible to derive a multitude of physical parameters (including star formation rates, stellar masses, and gas masses) which allow the interrelationship between star formation and gas content to be assessed in a statistically significant manner. In particular, modern wide field surveys (combined with deep, volume-limited data) allow trends to be analysed across many orders of magnitude in galaxy mass and star formation rate, shedding light on the global properties of galaxies in the local Universe. Moving to higher redshift, I discuss targeted observations of molecular gas in extreme star forming galaxies in the early Universe. These 'sub-millimetre' galaxies number amongst the most luminous objects ever discovered, and molecular gas observations have the power to uncover many of their physical properties, including their morphologies, kinematics, and star formation behaviour. I begin by presenting high-resolution observations of a small number of these galaxies at z rv 2, and discussing the implications for galaxy evolution studies. The final chapter of this thesis consists of the results of a survey for molecular gas in sub-millimetre galaxies conducted over the last decade, which represents the largest single study of molecular gas in the early Universe to date.

Interstellar chemistry has been a growing field over the last several decades. There is particular interest on the nature and reactivity of interstellar molecules; most notably that of polycyclic aromatic hydrocarbons (PAHs). My thesis focused on the kinetics of unimolecular dissociation of small PAH and PAH-like molecules under interstellar conditions. PAHs (naphthalene (NAP), anthracene (ANT) and pyrene (PYR)), some dihydro- equivalents (1,2-dihydronapthalene (DHN) and 9,10-dihydrophenanthrene (DHP)) and a few other small aromatic organic molecules (indene (IND), ethynylbenzene (EB), propynylbenzene (PB) and benzocyclobutene (BCB)) were studied using imaging photo-electron photo-ion coincidence spectroscopy (iPEPICO) and electron impact mass spectrometry (MS); both mass analyzed ion kinetic energy spectrometry (MIKES) and collision induced dissociation (CID). Experiments were performed at different ionization energies to produce breakdown diagrams for the various fragments. These diagrams are then fit using RRKM theory to determine the zero Kelvin activation energy (E0) and the entropy of activation (Δ‡S); these results are then compared and discussed. All these molecules were compared in order to try and find any overlying trends which could be applied to their role in the interstellar medium (ISM). It was determined that H loss was the dominant fragmentation channel, as it was the only dissociation channel common to the majority of molecules studied. It was also seen that organic fragment loss (C2H2, CH3 and C4H2) was only observed in smaller molecules which indicates that PAHs are not likely a source of these molecules. The small fragment molecules gave insight into the stability of closed ring structures, such as PAHs, through the comparison of the dissociation of closed and open structures. The dihydro-PAHs, selected as a probe to investigate the proposed catalytic role of PAHs in the formation of molecular hydrogen, yielded very interesting results. It was seen that these molecules would readily undergo isomerisation prior to dissociation. This added an unexpected level of difficulty to the calculations but quickly demonstrated how the presence of additional hydrogen atoms could greatly disrupt the dissociations, as it was not the simple process of removing them as it was originally believed. The overall trend observed was that it is the structure, not the size, which has the dominating effect on the dissociation. Ions of similar structure behaved similarly, regardless of a change in mass; isomers, however, had radically different behaviours which can only be attributed to their differing molecular conformations. This observation could aid in the understanding of larger PAHs, those which are believed to exist in the ISM, and what role they may play in the chemistry of the universe.

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.