This work presents a search for galaxies at 6.5 < z < 9.8 based on the Lyman-break technique, using the latest HST WFC3 near-infrared data covering ∼ 150 arcmin^2 of the GOODS-South field. With these data, it is possible to find sufficient z ≈ 7−9 galaxies to fit both φ∗ and M∗ of the UV Schechter luminosity function. There is evidence for evolution in this luminosity function from z = 6−7 to z = 8−9, in the sense that there are fewer UV-bright galaxies at z ≈ 8 − 9, consistent with an evolution mainly in M∗. The candidate z ≈ 7 − 9 galaxies detected have insufficient ionizing flux to reionize the Universe, and it is probable that galaxies below our detection limit provide a significant UV contribution. The faint-end slope, α, is not well constrained. Adopting a similar faint-end slope to that determined at z = 3 − 6 (α = −1.7), and a Salpeter initial mass function, reionization could be achieved at z ≈ 7 for an escape fraction of ionizing photons fesc = 0.5 integrating the luminosity function down to M_UV= −15, while at z ≈ 8, for the same fesc, the ionizing photon budget still falls short even integrating down to M_UV = −8. A steeper faint end slope or a low-metallicity population (or a top-heavy IMF) might still provide sufficient photons for star-forming galaxies to reionize the Universe, but confirmation of this might have to await the James Webb Space Telescope.

This thesis presents the measurement of the cosmic microwave background (CMB) power spectrum for the Atacama Cosmology Telescope (ACT) experiment and its polarized upgrade, ACTPol. I present the tools that I have developed for constructing unbiased and nearly optimal statistical estimators. I discuss how to separate the cosmological and the astrophysical signal and how to characterize instrumental systematics. The goal of this work is to obtain accurate power spectra measurement that can be used for cosmological parameter estimation. I first present the analysis of the complete ACT data set. The high resolution of the telescope allows us to recover power spectra to &ell; = 10000. I report the measurement of the power spectra at 148 GHz and 218 GHz, as well as the cross-frequency spectrum between the two channels. The power spectrum measurement is consistent with the ΛCDM model and a basic foreground model. I then present the cross correlation of maps from the Atacama Cosmology Telescope with maps from the Planck satellite in two overlapping regions covering 592 square degrees. I find excel- lent agreement between the two datasets at both frequencies, quantified using the variance of the residuals between the ACT power spectra and the ACT×Planck cross-spectra. The next generation of CMB experiments are focused on measuring its polarization. I present efficient algorithms for CMB lensing simulation and power spectrum estimation for flat-sky CMB polarization maps. Finally, I discuss the first temperature and polarization power spectra measurement from the ACTPol experiment. They are the first attempt to measure the polarization of the CMB at high resolution.

In this thesis I bring together three projects that comprise my postgraduate studies; using numerical simulations of galaxy formation in a cosmological context. The first of these projects involves the simulation of a suite of galaxies in loose group and field environments. This suite of galaxies is used to compare properties such as the metallicity gradients and morphology to determine if systematic differences are apparent as a function of subtle environmental differences. Almost no distinction is seen between galaxies in the field and the loose group environments: individual assembly histories of the galaxies dominate over ambient environmental effects with the exception of the vertical velocity dispersion of the stellar disc where loose group galaxies tend to exhibit a greater number of instances of impulsive heating of the disc. In the second project I present further analysis of this suite of galaxies and a comparison with other galaxies simulated using contrasting methodologies, in ad- dition to several semi-numerical galaxy formation models. The focus of this work is the evolution of metallicity gradients and star formation profiles, finding that galaxies form in an inside-out fashion. This leads to steeper metallicity gradients in young stellar populations at high redshift compared with the present day. By considering present day stellar populations with different ages in these galaxies the converse is found, older populations have flatter gradients. This suggests that while the metallicity gradient starts out steep, it flattens over time due to stellar migra- tion/mixing. This flattening due to stellar migration happens at a faster rate than the flattening of the gas phase metallicity gradient. Finally, I present an update to the N-body and adaptive mesh refinement hydrodynamical code ramses that introduces a more sophisticated feedback treatment, this code is dubbed ramses-ch. Under the new scheme, energetic and elemental feedback is contributed by stars throughout their lifetime rather than (as previously) in a single burst. This relaxation of the ‘instantaneous feedback approximation’ in ramses-ch opens up the opportunity for studying chemical evolution using adaptive mesh refinement hydrodynamics where previous studies were limited to smoothed particle hydrodynamical codes or semi-numerical models. The new code is applied to the simulation of a typical disc galaxy using different stellar initial mass functions and supernovae type-Ia progenitor models. The influence of these model inputs on the ratio of elemental abundances and supernovae rates in the simulated galaxies are compared as a means of constraining chemical evolution models. The conclu- sions drawn from this work are discussed in the broader context of galaxy formation simulations.

Galaxy groups and clusters are cosmic giants. They are the largest observable virialised objects that have materialised from the initial perturbations in the early Universe. These systems comprise of not only galaxies, but also hot gas and dark matter. They are ideal astrophysical laboratories to study the matter distribution of the Universe and cluster physics whilst their distribution and evolution can be used constrain cosmological parameters. Clusters are the ultimate test for the structure formation paradigm. However, for this to be achieved requires knowledge of their mass which is a particularly challenging task since there are no ‘cosmic scales’ to directly measure the masses of these objects. Groups and clusters are massive enough to gravitationally influence light emitted from background galaxies, an effect known as gravitational lensing. Its mass can be inferred from the strength of the weak lensing signal and is only dependent on the gravitational potential well depth. However, its limitations arise from systematic uncertainties of shape measurement, photometric redshift and shallow survey depth. This thesis concerns constraining accurate and precise cluster mass estimates of low mass groups and poor clusters, and testing the limits that can be achieved with current noisy, ground-based data.

Bibliography: p. 84-91. / ii, 91 p. ; 30 cm. / Title page, contents and abstract only. The complete thesis in print form is available from the University Library. / Thesis (Ph.D.)--University of Adelaide, Dept. of Physics and Mathematical Physics, 1994

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Bibliography: leaves 152-156 / ix, 156 leaves : ill ; 31 cm. / Title page, contents and abstract only. The complete thesis in print form is available from the University Library. / Thesis (Ph.D.)--University of Adelaide, 1986

No description available.

The galaxy stellar mass function (GSMF) has been well measured by the Galaxy And Mass Assembly (GAMA) survey down to a mass of $\mstar = 10^{8}\,\msun$. Below this mass the values produced so far can only be taken as lower limits on the distribution. One source of this incompleteness is failing to account for undetected low-surface-brightness galaxies (LSBGs) within the fields observed. These galaxies have been known about for some time, however, taking a true census of their population is difficult because of the biases associated with their detection in large surveys. The focus of this thesis is to improve the census of these objects and to try and apply those results to the low-mass end of the GSMF. First the SDSS data used to create the original GAMA catalogues is re-examined for low-surface brightness galaxies (LSBGs). To accomplish this SDSS DR7 imaging was used and a specialised detection algorithm created. This was based on masking sources detected with SDSS \textsc{photo}, combining the {\it gri} images with a weighting that maximises the signal-to-noise (SNR), and smoothing the images. These were then run through a detection algorithm which finds all pixels above a set threshold and groups them based on their proximity to one another. The list of detections is cleaned of contaminants such as diffraction spikes and the faint wings of masked objects. This produces a final list of 343 newly discovered LSBGs. Measuring their $g-i$ and $J-K$ colours shows that most are likely to be at redshifts less than 0.15. The photometry is carried out using a flexible auto aperture for each detection giving surface brightness measurements of $\mu_{r} > 23.7$\,mag arcsec$^{-2}$ and $r$-band magnitudes of $r_{AUTO} \gtrsim 20$\, mag. Through this method we show there are at least 343 new LSBGs within the GAMA fields, however none of these galaxies are bright enough to be within the GAMA main survey limit. It was noticed during the previous work that the detected LSBGs were all visible in VIKING $Z$-band data, and so it was decided to run a more traditional detection algorithm over these data to increase the number of LSBGs detected. This could then be used to create a new GSMF based on the deeper $Z$-band imaging. By using this imaging it will be possible to detect many more faint galaxies than previously and also increase the depth to which surface brightness can be effectively probed. The three GAMA equatorial regions have had mosaics created from the $Z$-band imaging which are searched using \textsc{Source Extractor} (\textsc{SExtractor}) and catalogues of detections are made. These are then compared to the original GAMA catalogues to remove duplicate detections and identify any possible new ones. Criteria are then applied to the source lists to remove any stars or objects which are either not galaxies or artefacts. This then leaves only likely galaxies in the catalogue to be used. The next stage is to create the GSMF based on the data collected, through applying corrections for the volume searched, and the spectroscopic completeness of the objects after they have been binned in $g-i$, $J-K$, and apparent magnitude. The GSMF created is compared to previous versions, namely that from \cite{Baldry+2012}, and a rise in the number density at masses of $\mstar \le 10^{8}\,\msun$ is shown. These can still only be thought of as lower limits however as improvement to the imaging can still be made in future surveys. With a full catalogue obtained using the VIKING Z-band it was decided to revisit the detection algorithm developed in Chapter 2. A pilot study was undertaken to both test the validity of the method, and the suitability of the VIKING images for further study. Whilst applying the detection algorithm to the data improved the ability to detect low surface brightness features within the images, no new galaxies were discovered over the pilot study area of $0.75$ deg$^{2}$. This method applied to the Z-band data, even over the full area, is unlikely to lead to large numbers of new LSBGs. This work has shown that there are still LSBGs in the field to be discovered. The result of finding new LSBGs has been to raise the measurement of the GSMF at low masses, further constraining the number of low mass galaxies in the Universe.

Cosmology is now a precision science. The temperature anisotropies in the cosmic microwave background (CMB) have been exquisitely mapped by many experiments over the last decade. The Planck satellite was launched in 2009, observed the sky in temperature and polarisation, and released the nominal mission temperature data to the public in 2013. Planck has shed new light on CMB polarisation anisotropies and the polarisation signal from our own galaxy, and knowledge of the galactic emission forms a central part of this analysis presented in this thesis. I first introduce the background cosmology and review what we know about CMB temperature and polarisation anisotropies, including their mathematical formulation and representation on the sphere. I review our knowledge of the origin of galactic polarised foregrounds, particularly electron synchrotron and thermal dust emission. I then describe the generation of polarised CMB maps from an input cosmological model, and the generation of CMB polarised foregrounds using a variety of methods to create full-sky maps of the microwave sky at the Planck observing frequencies between 30 and 353 GHz. I develop a parametric fitting maximum-likelihood polarised component separation routine with correlated foreground parameters to extract the CMB and associated foregrounds to a high precision, and show that my method can reliably recover a primordial B-mode polarisation signal at r = 0.1 at multiple map resolutions. I then test the sky model against the full mission Planck data to examine how accurately the foregrounds are simulated, and find that along the galactic plane the simulations are accurate, but at high latitudes the agreement worsens. I also compare the polarisation morphology to that seen in the WMAP data and find a tension between Planck and WMAP. I present an analysis of the dx8 polarisation data in terms of polarised amplitudes and orientations, and investigate a variety of foreground separation routines to get a feel for the reliability of the data. Significant systematic issues are found and I conclude that in their current state, the polarisation data are not reliable enough for precise cosmology. Finally I develop a Fisher matrix analysis of the temperature power spectrum using the full mission covariance matrix to explore the parameter space around a CosmoMC simulation, and extract the principal components for different models. I use this to explore a strange oscillation in the power spectrum and conclude that it is a statistical fluke, a conclusion confirmed in a recent data release. I close by offering extensions to the work and a look into the future of the field.