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.

I carried out systematic studies on the assembly history of dark matter halos, using numerical simulations and semi-analytical methods. First, I look into dark halo mass assembly history. I confirmed that the halo mass assembly is divided into a fast accretion phase and a slow accretion phase. These two phases are found to be separated by the epoch when the dark halo potential reaches its maximum. The fast accretion phase is dominated by mergers, especially major mergers; the slow accretion phase is dominated by slow mass accretion. Each halo experiences about 3±2 major mergers since its main progenitor had a mass equal to 1 percent of halo mass. However, the average redshift at which these major mergers occur is strongly mass dependent. Secondly, I investigate the formation times and the assembly bias of dark halos. I use eight different definitions of halo formation times to characterize the different aspects of the halo assembly history. I find that these formation times have different dependence on halo mass. While some formation times characterize well the hierarchical nature of halo formation, the trend is reversed for other definitions of the formation time. In addition, the formation-time dependence of halo bias is quite strong for some definitions of formation time but weak or absent for others. Thirdly, I study sub-halo mass function in the halo assembly history, with the generally known unevolved sub-halo mass functions (USMFs). I find that for subhalos that merge into the main progenitor of a present-day halo, their USMF can be well described by a universal functional form; the same conclusion can also be reached for the USMF of all sub-halos that have merged during the entire halo merging history. In these two cases, the USMFs do not seem to depend on the redshift of the host halo either. However, due to the mass loss caused by dynamical effects, only small part of the accreted halos survived and became sub-structures in the present-day dark halos. In the cluster-sized halos, 30% survived sub-halos are sub-subhalos. The sub-halo mass function at given accretion time (redshift) is also investigated to find the origin of the statistics mentioned above.

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.

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Environment plays an important role in the evolution of galaxies. In particular, denser environments, such as galaxy clusters and large-scale field filaments of the cosmic web have been found to reduce star formation in galaxies. The intersection of these environments provides an interesting regime of study. We investigate how cosmic filaments impact the quenching of galaxies within one virial radius of 324 simulated clusters. We use hydrodynamic runs from The Three Hundred Project along with the cosmic web extractor DisPerSE to track filaments and the structure finder VELOCIraptor to identify halos hosting galaxies. Limited by the resolution of the simulation, we examine star formation indirectly by way of galaxy colour and cold gas fraction. We find that cluster galaxies residing closer to filaments tend to be star-forming, bluer, and contain more cold gas than their counterparts further away from filaments. This is in stark contrast with galaxies residing outside of clusters, where galaxies close to filaments show clear signs of density related pre-processing. Careful examination of flows around and into cluster galaxies strongly suggests that the colder, dynamically coherent hydrodynamic streams along intra-cluster filaments partially shield galaxies close to them from strangulation by the hot, dense intra-cluster medium. These streams, in addition to the reduced density contrast of intra-cluster filaments with the intra-cluster medium, also limit the ram pressure stripping experienced by cluster galaxies. We further examine stripping in the context of gas disturbances in phase space to create a classification for wet and dry galaxies. / Thesis / Master of Science (MSc)

Most small asteroids are defined as "rubble-piles," or bodies with zero tensile strength and large bulk porosity that are tenuously held together by cohesive forces. Improving the accuracy of predictions of asteroid strengths requires suitable laboratory measurements of relevant materials, as well as increasing the availability of materials from sample return. In this work, we use Atomic Force Microscopy (AFM) force measurements and particle characterization to characterize, evaluate, and decouple variables that affect cohesive forces that act between micron-sized grains. In our first investigation we explored interactions of JSC-1 lunar simulant grains using three sample sizes, three spherical AFM tip diameters, and varying relative humidity, observing that the results are very dependent on the RH and, by proxy, adsorbed water. We observed weaker adhesion with larger grain/tip size, which can be attributed to the changing contact area between the samples and the tips. We next performed experiments in vacuum conditions and characterized the cohesive values of a high-fidelity CI simulant (Exolith) based on the CI1 meteorite Orgueil. Our results show no significant trend in adhesion, but we do observe that some correlating characteristics of the grains, such as roughness, can dominate the work of adhesion. The chemical nature of the grains, including their affinity for water, also played a role in if they became more adhesive in vacuum conditions or less adhesive in vacuum conditions. Our studies decouple several factors that contribute to the complex physics of adhesion and even more complex idea of understanding adhesion in a space environment with irregularly shaped grains. This approach will pave the way to a better understanding of regolith surface properties, improve contact models for irregularly shaped particles, and provide suitable inputs for models of asteroid cohesion. This analysis technique can be used on future materials provided by sample return missions.

It is now well established that a substantial fraction of all galaxy assembly occurs in intense bursts of star formation and black hole accretion, but the role of these two modes and how much they affect one another remains unclear. We thus investigate this in three complementary studies. In the first, we assemble a sample of 513 quasars identified by the Sloan Digital Sky Survey with detections by Herschel. These objects span a redshift range of 0 < z < 4, and their SEDs give a mean SFR of ~1000M☉/year. When comparing these SFRs to the intrinsic properties of the quasars, we find no clear connections between the quasars and the ongoing star formation events in their hosts. We then look for evidence of AGN feedback in broad absorption line (BAL) quasars, as such features are indicative of outflowing material. We find that high-ionization BAL quasars have indistinguishable properties to those of classical quasars. In our second study, which describes an iron low-ionization BAL quasar, SDSS J121441.42-000137.8, our results are again consistent with no feedback. Thus, it seems unlikely that feedback plays a dominant role in quenching star formation at the extreme SFRs seen in our BAL objects. We lastly study the host of an optically-bright quasar, SDSS J160705.16+355358.6, with evidence of an ongoing merger. We create the Point Spread Function (PSF) using a star that is in the same part of the field as our object, a method which is relatively unexplored. By subtracting the PSF, we are able to extract some of the host properties. We compare two PSF creation methods and find the empirical approach to be superior. Fits to the SEDs of the two galaxies are consistent with both falling on or above the main sequence of star formation. It is additionally plausible that these two galaxies could coalesce into a single massive quiescent galaxy by z ~ 2, and thus serve as progenitors to this class of galaxy that has proven challenging to our understanding of galaxy assembly. / Doctor of Philosophy / Quasars are among some of the brightest objects in the Universe and are powered by supermassive black holes that are rapidly accreting new material. The light from these distant objects can be detected across the electromagnetic spectrum, with each wavelength regime offering new insight into their properties. Further, if we look at their spectra, the features appear redshifted, i.e. they are at longer wavelengths compared to the expected values on Earth. More distant objects have higher redshifts. This, coupled with the constant speed of light, tells us that light from a quasar that has reached us on Earth must have been emitted many years ago; in other words, quasars offer glimpses into the past and can be used study how our Universe has assembled over time. Star formation and quasar activity in galaxies have been shown to coexist across all redshifts. This suggests a deep connection between a galaxy's stellar and black hole mass assemblies. Both peak at z ~ 2, implying that a substantial amount of all galaxy assembly took place in high-redshift, dusty bursts of star formation and quasar activity. This dust absorbs light originally emitted at optical/UV wavelengths and reradiates it in the infrared, making infrared wavelengths the perfect regime in which to investigate the connection between the two processes. In this dissertation, I have focused specifically on quasars with detections at both optical and far-infrared (FIR) wavelengths to determine what effect, if any, quasars have on the galaxies in which they reside. The optical emission of these systems describes the properties of the quasars, while the FIR estimates star formation rates (SFRs) in their hosts. Many astronomers invoke something called feedback, in which the quasar regulates the host star formation, to align theory with observations. We search for evidence of this process in the very bright quasars located within extremely star-forming systems. We, however, find no such evidence. This could imply that, at the high luminosities of our systems, feedback is not the dominant effect in regulating star formation, but perhaps some host self-regulation is instead. It could also imply that the feedback timescale is much shorter than that of either quasar or extreme star formation activity, making direct observations of feedback difficult.

The Magellanic System at a distance of 50 kpc from the Milky Way (MW), is a prime target in the study of stellar populations, star formation histories and galactic dynamics in low metallicity environments. The Large Magellanic Cloud (LMC) and Small Magellanic Cloud (SMC) have been observed in great depth, however there has been somewhat less interest in the Magellanic Bridge connecting the two and only more recently has the interest surged in the Magellanic Stream, which trails the Clouds between them and the MW. The Magellanic Bridge has a known younger stellar population dating back to Irwin’s observations (Irwin et al., 1990), only more recently has an older population been confirmed in the Bridge by Bagheri et al. (2013) and No¨el et al. (2013), while the Magellanic Stream is known to contain gas only with no stellar component. The estimated ages of the Bridge and Stream are 200 Myr (Bekki, 2007) and 2 Gyr (Diaz and Bekki, 2012) respectively, with the postulated Bridge formation from a tidal interaction between the Clouds. The formation of the Stream is less well understood with different models using varying assumptions and parameters such as Besla et al. (2012) and Nidever et al. (2010), including possibilities that the Clouds were historically bound or un-bound, and that the MW may or may not have been involved in the Stream formation. The work in this thesis makes use of different methods of removing the Galactic foreground population in the direction of the Magellanic Bridge and Stream to create cleaned catalogues of these regions. Various methods of analysis are applied to the cleaned catalogues in this work to identify stellar populations in the Bridge and Stream and density variations in the Bridge, including the production of CMDs and two-colour diagrams, fitting isochrones to the observational data, creating stellar density maps and studying spatial variations. This work contains the first published confirmation that the Bridge contains an older population of stars from public catalogues, which is supported with observations of the older population in recent deeper surveys, and confirmed with spectroscopic follow up observations. The young population has ages within the age of the Bridge ( 200 − 500 Myr) and are likely to have formed in-situ, in regions of high density gas closest to the SMC. The number of young blue objects in the Bridge tiles is greater towards the SMC and decreases towards the LMC. Populations identified here reach ages up to 3 Gyr are likely to have been drawn into the Bridge from the Clouds at formation. The key results from this work are that an older Bridge stellar population has been identified and confirmed, indicating that stars as well as gas were drawn into the Bridge at its creation. The fact that the younger population has the highest density away from the main concentration of hydrogen show that the gas within the Bridge has been displaced by ram pressure, most likely due to the Clouds moving through the Galactic halo. Less concrete results in this work reveal a puzzling populetion of objects within the Magellanic Stream, which could be stellar in nature and with follow up work, could be the first observation of Stream objects. This work contributes to our understanding of the interaction between the LMC and SMC via the Stellar populations between them.

The role of the Anthropic Principle in astrophysics and cosmology is examined in two principal parts. The first (minor) part takes a chiefly philosophical perspective and examines the manner in which human cognition features into discussions on cosmic origins. It is shown that the philosophical questions raised by the Anthropic Principle and ‘fine-tuning of life’ bear resemblances to problems within the philosophy of mind and we seek a common origin for this surprising parallel. A form of ‘epistemic structural realism’ is defended and used to critique the physicalist identity thesis. It is argued that equating ‘reality’ with mathematical structures, which is the basis of the identity thesis, leads to incoherent conclusions. Similar reasoning is used to critique infinite Multiverse theories. In the second (major) part, we gradually transition into mainstream astrophysics, first presenting a new line of research to explore counterfactual universes using semi-analytic models (SAMs) and offering a preliminary study wherein the cosmological constant is varied and the effects on ‘advanced civilisations’ are examined. The importance of galaxy mergers is highlighted and leads to their study. We first try solving the pattern-recognition problem of locating mergers using the Galaxy Zoo database and produce the largest homogenous merger catalogue to date. We examine their properties and compare them with the SAMs of the Millennium Simulation finding good general agreement. We develop the Galaxy Zoo approach with a new visual-interface design and double the size of the merger catalogue of SDSS mergers in the local Universe.