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This thesis investigates weak lensing (WL) of galaxies and the cosmic microwave back- ground (CMB) in the nonlinear regime. WL describes the effect of bending of background light rays by foreground matter (“lens”). It is sensitive to the large scale structure of the universe, and hence is a promising method to answer some unsolved fundamental questions in physics, such as the nature of dark energy and the total mass of neutrinos. WL datasets of unprecedented precision will come on-line in the early 2020s. This presents an exciting yet challenging task for the WL community: how do we extract the maximum amount of information from lensing observables, while minimizing the impact of systematics? This work attempts to answer this question by studying non-Gaussian statistics. Traditionally, WL data are analyzed using second-order statistics, which capture all the cosmological information if the density field is Gaussian. However, the small-scale density fluctuations are strongly non-Gaussian and can be highly sensitive to cosmology. Thus we need higher order (non-Gaussian) statistics to utilize these features in the nonlinear regime. In this thesis, we study the constraining power on cosmology and relevant systematics of non-Gaussian statistics, with a focus on convergence peaks. We present the first cosmological constraints using peak counts of the CFHTLenS survey. We also quantify the impact of magnification and size bias, one type of lensing systematics, on the lensing power spectrum and peaks. Finally, going beyond galaxy lensing, we cross-correlate Planck CMB lensing maps with CFHTLenS galaxy lensing maps, to investigate various WL systematics.

Lenticular and elliptical galaxies, collectively referred to as "early-type galaxies" (ETGs), are commonly thought to represent the end-points of galaxy evolution. Lying in the red sequence of galaxies, these objects are defined by their mostly old stellar populations and by their "red and dead" appearance in optical observations. Much progress in understanding these objects has been made with integral-field spectroscopy in recent years, with results repeatedly pointing to a link between early-type galaxies and high-redshift spiral galaxies. However, the exact nature of this link remains unclear, with a wide variety of evolution scenarios likely required to fully explain the range of observed early-type galaxy properties. In my study, I analysed observations of twelve early-type galaxies taken with the Mitchell Integral-Field Spectrograph at McDonald Observatory, Texas. These galaxies have previously been found to contain detectable quantities of neutral hydrogen gas, with ten out of the twelve displaying large-scale hydrogen disks. I extracted line-of-sight kinematics of the stellar and ionised gas components of these galaxies, and I used various modelling approaches to constrain their stellar population parameters as well as their three-dimensional mass structure in terms of both dark and visible components. An important feature of this study is the wide field of view of the spectroscopic observations, which reach beyond two half-light radii for almost all of the sample; this remains rare for integral-field unit (IFU) studies of ETGs, and so sets this study apart from most earlier works. The gas-rich nature of the sample is likewise novel. I find all aspects of my analysis to yield a consistent view of these galaxies' evolution, in which one or more gaseous interaction events served to shape them into their observed forms. I find these galaxies to contain low dark matter fractions on average within the inner half-light radius, and I also find mass modelling to favour near-isothermal total density profiles over much of the sample.

"July 2003." / Bibliography: p. 203-211. / xxii, 211 p. : ill. (some col.) ; 30 cm. / Title page, contents and abstract only. The complete thesis in print form is available from the University Library. / Investigates properties of magnetic fields in galaxy clusters via both statistical Faraday rotation measures and diffuse source polarimetry, and investigates the nature and generation mechanisms for diffuse radio emission in the ACO cluster A3667. / Thesis (Ph.D.)--University of Adelaide, Dept. of Physics and Mathematical Physics, 2003

Large stellar surveys are revealing the chemodynamical structure of the Galaxy across a vast spatial extent. However, the many millions of low-resolution spectra observed to date have not yet been fully leveraged. In chapters 2 and 3, we employ data-driven spectroscopic models to the low-resolution LAMOST survey (𝑅 = 1800). In chapter 2, we employ The Cannon, a data-driven approach for estimating chemical abundances, to obtain detailed abundances, using the GALAH survey as our reference. We deliver five (for dwarfs) or six (for giants) estimated abundances representing five different nucleosynthetic channels, for 3.9 million stars, to a precision of 0.05 - 0.23 dex. Using wide binary pairs, we demonstrate that our abundance estimates provide chemical discriminating power beyond metallicity alone. We show the coverage of our catalogue with radial, azimuthal and dynamical abundance maps, and examine the neutron capture abundances across the disk and halo, which indicate different origins for the in-situ and accreted halo populations. LAM- OST has near-complete Gaia coverage and provides an unprecedented perspective on chemistry across the Milky Way. Stars with unusual levels of enrichment in a particular element are of great interest, but often pose a problem for data-driven methods. In chapter 2, we present a simple method, for the de- tection of 𝑋-enriched stars, for arbitrary elements ?, even from blended lines. Our method does not require stellar labels, but instead directly estimates the counterfactual unrenriched spectrum from other unlabelled spectra. We apply this method to the 6708 Å Li doublet in LAMOST DR5, identifying 8,428 Li-enriched stars seamlessly across evolutionary state. We comment on the ex- planation for Li-enrichement for different subpopulations, including planet accretion, nonstandard mixing, and youth. The Galactic disk exhibits complex chemical and dynamical substructure thought to be induced by the bar, spiral arms, and satellites. In chapter 4, rather than calculating spectroscopic quantities, we use them to understand the Milky Way. We explore the chemical signatures of bar resonances in action and velocity space and characterize the differences between the signatures of corotation and higher-order resonances using test particle simulations. Thanks to recent surveys, we now have large datasets containing metallicities and kinematics of stars outside the solar neighborhood. We compare the simulations to the observational data from Gaia EDR3 and LAMOST DR5 and find weak evidence for a slow bar with the “hat” moving group (250 km s⁻¹ ≲ 𝑣_𝜑i ≲ 270 km s⁻¹) associated with its outer Lindblad resonance and “Hercules” (170 km s⁻¹ ≲ 𝑣_𝜑 ≲ 195 km s⁻¹) with corotation. While constraints from current data are limited by their spatial footprint, stars closer in azimuth than the Sun to the bar’s minor axis show much stronger signatures of the bar’s outer Lindblad and corotation resonances in test particle simulations. Future datasets with greater azimuthal coverage, including the final Gaia data release, will allow reliable chemodynamical identification of bar resonances. Finally, in chapter 5, we present KORG, a new package for 1D LTE (local thermal equilib- rium) spectral synthesis, which computes theoretical spectra from the near-ultraviolet to the near- infrared, and implements both plane-parallel and spherical radiative transfer. It is compatible with automatic differentiation libraries, and easily extensible, making it ideal for statistical inference and parameter estimation applied to large data sets. We outline the inputs and internals of KORG, and compare its output spectra to those produced by other codes. We use five example wavelength regions across 3660 Å – 15050 Å to show that the residuals between KORG and the other codes are no larger than that between existing codes themselves. We show that KORG is 1–100 times faster than other codes in typical use.

A galaxy's angular momentum is known to be correlated with its morphology: at a given mass, spiral galaxies have higher angular momenta than elliptical galaxies. A galaxy's angular momentum is also largely set by its formation history: in particular, how much gas and the kinematic state of the gas that both accretes onto it and is expelled in galactic outflows from AGN and supernovae. All gas inflowing to and outflowing from the galaxy interacts with gas in the region surrounding the galaxy called the circumgalactic medium (CGM), which means at a fundamental level, the CGM controls the angular momentum of the galaxy. Therefore, to really understand the origins of galactic angular momentum, it is necessary to understand the angular momentum of the CGM itself. In this dissertation, I present a series of projects aimed at studying angular momentum in the CGM using the Illustris and IllustrisTNG cosmological hydrodynamical simulations suites. In an appendix, I also present a project on searching a survey of neutral hydrogen for previously undetected ultra-faint dwarf galaxies in and around the Milky Way's CGM. First, to understand how present-day galaxies acquire their observed angular momentum, I analyze the evolution of the angular momentum of Lagrangian gas mass elements as they accrete onto dark matter halos, condense into Milky Way-scale galaxies, and join the z=0 stellar phase of those galaxies. I find that physical feedback from the galaxy is essential in order to produce reasonable values of galactic angular momentum, and that most of the effects of this feedback occur in the CGM, necessitating studying the angular momentum of the CGM itself. Following on from this result, I then characterize the angular momentum distribution and structure within the CGM of simulated galaxies over a much larger range of halo masses and redshifts, with the goal of determining if there are common angular momentum properties in CGM populations. I indeed find that the angular momentum of the CGM is larger and better aligned around disk galaxies that themselves have high angular momentum. I also identify rotating structures of cold gas that are generally present around galactic disks. This clear connection of the CGM to the galaxy motivated a detailed comparison to observations of cold CGM gas. I perform this comparison in the following chapter where I use the highest-resolution simulation from the IllustrisTNG suite of cosmological magneto-hydrodynamical simulations to generate synthetic observations of cold CGM gas around star-forming galaxies in order to study kinematics and compare them to line-of-sight observations of cold gas near comparable galaxies. With this direct comparison to observations of the CGM, I show that IllustrisTNG produces rotating CGM gas consistent with observations to a high degree. In the penultimate chapter I present unpublished work where I begin to examine angular momentum evolution in the CGM on much finer timescales than can be resolved with the cosmological simulations I have used thus far. Preliminary results suggest that gas can experience large changes in angular momentum very quickly, and that these changes may be connected to corresponding changes in the temperature of the gas. Finally, I conclude by summarizing my main results and briefly discussing what questions still remain unanswered and my plans and strategies for pursuing these questions in my future work.