In this Thesis we investigate the evolutionary histories of faint field galaxies using extremely deep optical and near-infrared photometry. Our work is centred on a 50 arcmin(^2) region at high galactic latitude which we call "The William Herschel Deep Field" (WHDF). In this work we describe three new near-infrared surveys of this field. In considering both this infrared data and the existing optical data, our broad aims are to increase our understanding of both the growth of galaxy clustering in the Universe and also to determine the star-formation histories of the field galaxy population. We consider our observations primarily in the context of luminosity evolution models in low density universes, but alternative scenarios are considered. Near-infrared galaxy counts derived from our catalogues are consistent with the predictions of our models, without the need for a steep faint-end slope for the galaxy luminosity function. We find that optical-infrared colour distributions of infrared-selected galaxies in the WHDF are deficient in red, early-type galaxies. This is consistent with the predictions of evolutionary models in which these systems have a small amount of on-going star-formation. We measure the amplitude of galaxy clustering in the WHDF for galaxies selected in optical and near-infrared bandpasses using the projected two-point correlation function. By comparing our measured clustering amplitudes with the predictions of our models we find that in all bandpasses the growth of galaxy clustering is approximately fixed in proper co-ordinates, again assuming a low-density Universe. Finally, an analysis of errors on the correlation function measurements suggest that discrepancies between our work and those of other authors may be explained by an underestimation of statistical errors.

Clusters of galaxies are host to powerful Active Galactic Nuclei (AGN) that greatly affect the thermal history of clusters. By keeping X-ray emitting gas from cooling, massive, run away star formation does not occur in the brightest cluster galaxy (BCG). This is achieved through radio jets displacing large quantities of metal-rich gas and carving out cavities in the intracluster medium (ICM). This metal-rich gas was originally formed within the BCG and ejected through type Ia supernovae. The current distribution of the ejecta suggests an extra source of energy has spread the material far out into the ICM. Currently, it is unclear what mechanisms are responsible. In this thesis, I present evidence, in the form of X-ray imaging and spectra, that establishes a link between AGN and the observed distribution of metal-rich gas. First, the BCG in the Abell 1664 cluster is unusually blue and is forming stars at a rate of ~23 solar masses per year. The BCG is located within 5 kpc of the X-ray peak, where the cooling time of 3.5×10^8 yr and entropy of 10.4 keV cm^2 are consistent with other star-forming BCGs in cooling flow clusters. The cooling rate in this region is roughly consistent with the star formation rate, suggesting that the hot gas is condensing onto the BCG. We use the scaling relations of Birzan et al. (2008) to show that the AGN is underpowered compared to the central X-ray cooling luminosity by roughly a factor of three. We suggest that A1664 is experiencing rapid cooling and star formation during a low-state of an AGN feedback cycle that regulates the rates of cooling and star formation. Modeling the emission as a single temperature plasma, we find that the metallicity peaks 100 kpc from the X-ray center, resulting in a central metallicity dip. However, a multi-temperature cooling flow model improves the fit to the X-ray emission and is able to recover the expected, centrally-peaked metallicity profile. Next, using deep Chandra observations of the Hydra A galaxy cluster, we examine the metallicity structure near the central galaxy and along its powerful radio source. We show that the metallicity of the ICM is enhanced by up to 0.2 dex along the radio jets and lobes compared to the metallicity of the undisturbed gas. The enhancements extend from a radius of 20 kpc from the central galaxy to a distance of ~120 kpc. We estimate the total iron mass that has been transported out of the central galaxy to be between 2E7 and 7E7 solar masses which represents 10% - 30% of the iron mass within the central galaxy. The energy required to lift this gas is roughly 1% to 5% of the total energetic output of the AGN. Evidently, Hydra A’s powerful radio source is able to redistribute metal-enriched, low entropy gas throughout the core of the galaxy cluster. The short re-enrichment timescale < 1E9 yr implies that the metals lost from the central galaxy will be quickly replenished. Finally, we present an analysis of the spatial distribution of metal-rich gas in 29 galaxy clusters using deep observations from the Chandra X-ray Observatory. The BCGs have experienced recent active galactic nucleus activity in the forms of bright radio emission, cavities, and shock fronts embedded in the hot atmospheres. The heavy elements are distributed anisotropically and are aligned with the large-scale radio and cavity axes. They are apparently being transported from the halo of the BCG into the ICM along large-scale outflows driven by the radio jets. The radial ranges of the metal-enriched outflows are found to scale with jet power as R ~ P^0.43, with a scatter of only 0.42 dex. The heavy elements are transported beyond the extent of the inner cavities in all clusters, suggesting this is a long lasting effect sustained over multiple generations of outbursts. Black holes in BCGs will likely have difficulty ejecting metal enriched gas beyond 1 Mpc unless their masses substantially exceed 1E9 solar masses. It is likely however for these black holes to output enough energy to uplift all the peaked, metal-rich gas beyond the BCG to the currently observed widespread distribution.

This thesis describes the construction and application of the Edinburgh/Durham Southern Galaxy Catalogue, which is a database of information on ~ 1-5 million galaxies, covering ~ 2000 deg2 of the South Galactic Cap. This catalogue is based on objective image detection and classification techniques, rather than the visual searches of photographic plates used in previous galaxy catalogues. The raw data for this project are digitised scans of 60 ESO/SERC Atlas plates using the COSMOS high-speed plate measuring machine. The quality controls employed during the production of the ESO/SERCAtlas, ensures that it is deeper and more uniform than set of plates used previously to construct a galaxy catalogue. The COSMOS machine objectively detects and parameterises ~ 2 X 105 images on each photographic plate. Image deblending software has been introduced to ensure the accurate detection and parameterisation of images in the crowded regions of compact clusters. Star-galaxy classification and photometric calibration techniques have been investigated and optimised to reduce and quantify any systematic variations that could introduce spurious structure. A classification algorithm has been used to automatically classify images over the whole range of magnitudes in the survey. Accurate intra-plate pho?tometry is possible for galaxies, because a COSMOS magnitude can be defined which is linearly related to the object magnitude. Inter-plate calibration is carried out using CCD galaxy sequences for every second field in the catalogue. Unlike global calibration techniques used previously, this arrangement of CCD?s prevents propagation of calibration errors. Statistics are given to show that the final catalogue of galaxies will be > 95% complete for bj < 20-0 with < 10% contamination by stars and that the point- to-point variation in galaxy number density, due to the combined residual systematic errors in classification and calibration, is ~ 8%. To date a mosaic of 35 plates covering a contiguous region of 1000 deg2 has been constructed. The large-scale galaxy distribution, seen in maps of this data, is dominated by two large supercluster complexes separated by ~ 15? ? 20?. Several filamentary arc structures can also be seen, with clusters distributed along them. The number- magnitude counts derived from this database show significant deviation from a no?evolution model at bj > 18-75. The variation in the amplitude of the counts across the survey cannot be accounted for by systematic variations in limiting magnitude and so is probably due large-scale clustering of galaxies. The two-point correlation functions calculated for this 35-plate mosaic confirm a break from power-law, though at larger scales (~ 20h-1 Mpc ) than previously estimated. In the context of current theories of galaxy formation, models involving standard cold dark matter with extra large-scale power would still seem to be excluded.

No description available.

In this thesis, we present a novel algorithm for computing the radiation field in astrophysical simulations. The algorithm is tree-based, similar to many gravity solvers, and allows computation of radiative transfer in O(Nsink logNsource) in cases without absorption, and O(Nsink logNsource logN) time with absorption. The algorithm scales well with the number of processors due to its tree-based nature, and is highly tunable in accuracy and speed. It is also only weakly dependent on both the energy band and the number of energy bands used. We provide a suite of tests of the code showing its ability to create accurate fluxes, ionization fronts, hydrodynamics coupling, and shadowing. We apply the algorithm in a set of simulations on an isolated spiral galaxy from the AGORA project. The algorithm is used to calculate FUV fields within the galaxy, which self-consistently sets the dominant photoelectric heating in the gas. This has never before been performed in galaxy simulations. We find, in agreement with Ostriker et al. [2010], that FUV can be a very important regulation mechanism for star formation in a galaxy. Depending on the assumed opacity, FUV can decrease the average star formation rate (SFR) anywhere from 15% to a factor of twenty. We compare this regulation mechanism to a highly effective model of supernovae (SNe) feedback, which reduces the SFR by a factor of twenty as well. However, SNe feedback destroys most of the gas structure in the process, whereas FUV has minimal impact on the gas structure. In the simulations with FUV radiation, we are also able to create a two phase medium that is a function of the mean FUV intensity the gas receives. Finally, we find that simulations with FUV agree well with observations of nearby spirals on the Kennicutt-Schmidt relation, at least at gas surface densities of 0.2 - 30 M⊙. At surface densities higher than 30 M⊙, we find that FUV is not an effective regulator which is consistent with arguments that SNe or other feedback mechanisms should become the primary regulator. / Thesis / Doctor of Philosophy (PhD)

Comets and Centaurs are icy remnants from the formation of the solar system. Analyzing the physical properties of their nuclei and their production rates can serve as powerful tools for tracing primitive solar system material. The four research projects in this dissertation examine these properties in comets and Centaurs. The first project focuses on observations of main belt comet 176P/LINEAR that were obtained with the Kepler space telescope. Optical lightcurves were used to constrain models of the nucleus's spin pole axis, shape and activity level. The second project used millimeter-wavelength spectra from the Arizona Radio Observatory Submillimeter Telescope and infrared photometry of Spitzer images to derive production rates of CO and CO2 from Oort Cloud comet C/2016 R2 (PANSTARRS). The third project is a compendium of CO, CO2, and H2O production rates in more than 25 comets and Centaurs that were obtained with a variety of space-based and ground-based telescopes and which were analyzed to test models of comet formation and evolution. CO, CO2, and H2O are the most abundant molecules observed in comets. The combination of these three molecules are likely the largest sources of elemental oxygen in the gas comae of comet and therefore a close approximation of the oxygen released in the comae. One key result of the survey is that CO/CO2 production rate ratios appear largely heliocentric dependent, with more CO produced the farther the comet is from the Sun. One exception is dynamically new comets which typically produce more CO2 than CO which is in predicted by models of significant cosmic-ray processing over time. The fourth project produced the first CO2 detection in a Centaur (39P/Oterma), which shows significant differences between the CO/CO2 in 39P and 29P, another Centaur, which may be partly due to different heating and processing histories.

Galaxies in the Universe are primarily blue and star-forming or red and passively evolving. Here we study an outlier population of red, star-forming galaxies in the local Universe which we call Red Misfits. These galaxies are classified based on inclination-corrected optical colours and specific star formation rates derived from the Sloan Digital Sky Survey Data Release 7. We find that $\sim$11 per cent of galaxies at all stellar masses are classified as red in colour yet actively star-forming. Using the wealth of information provided by the SDSS and related products we explore a number of properties of these galaxies and demonstrate that Red Misfits are a distinct population of galaxies in the Universe and not simply blue star-forming galaxies whose colours are reddened by intrinsic dust extinction. Red Misfit galaxies exhibit intermediate, bulge-dominated disk morphologies, intermediate stellar ages, slightly enhanced dust extinction and gas-phase metallicities, and an enhanced likelihood of hosting an active galactic nucleus. The proportion of Red Misfits in galaxy groups remains constant irrespective of group halo mass or projected distance to the group centre. We conclude that Red Misfits are a transition population being gradually quenched on their way to the red sequence and that this quenching is dominated by internal mechanisms rather than environmentally-driven processes. / Thesis / Master of Science (MSc)

The stellar populations harboured by some of the Universe’s earliest galaxies are within observational reach. Determining the details of these stellar populations and their formation histories within the first billion years after the Big Bang is crucial for both understanding the earliest stages of galaxy evolution and for assessing the contribution of early star-forming galaxies to cosmic reionization. This thesis presents observational measurements of the rest-frame UV and optical colours of star-forming Lyman Break galaxies (LBGs) at redshifts 4 < z < 9, and their inferred stellar population parameters. By combining ground-based ~1 deg² surveys with deeper, narrower space-based deep-field surveys, we have constrained the rest-frame UV spectral slope of galaxies over a wide-range of cosmic time (4 < z < 9) and luminosity (−23 < MUV < −17) in a self-consistent way. To do so, we developed simulations to allow the inference of intrinsic colours from noisy, potentially biased observations. With these simulations, a robust UV colour measurement method was devised in preparation for the Hubble Ultra Deep Field 2012 (UDF12) survey. Then, after delivery of the UDF12 data, our technique and simulations were applied to yield the first bias-free measurements of the UV spectral slope of galaxies at z ≈ 7 and 8. We found no support for the previously claimed dominant sub-population of exotically blue, faint galaxies at z ≈ 7. In fact with careful consideration of their errors and selection biases, even the most extreme galaxies we observed can have their colours explained by stellar population synthesis models of unremarkable parameters. Expanding this study to brighter, rarer, galaxies required the inclusion of wide-area ground-based survey data, and consequently a more focused examination of galaxies at z ≈ 5. We selected high signal-to-noise galaxies from four fields, with absolute magnitudes spanning MUV = −22.5 to −17.5, and measured their rest-frame UV spectral slopes. Coupling these measurements with our simulated observations, we were able to determine the width of the intrinsic colour distribution of galaxies at z ≈ 5. We found that brighter galaxies are not only on average redder than their fainter counterparts, but they are also less self-similar in their colours. The redder average UV colours of brighter galaxies can be attributed to those galaxies being either older, or more dust reddened. By pairing these measurements, which are primarily a probe only of the presently forming portion of the stellar population, with those of LBG’s Balmer Breaks, which are more sensitive to bygone star formation, we were able to break this age–dust degeneracy and conclude that, at z ≈ 5, brighter galaxies are more heavily reddened than fainter galaxies even though their stars are no older.

The circumnuclear disc (CND) orbiting the Galaxy's central black hole is a reservoir of material that can ultimately provide energy through accretion, or form stars in the presence of the black hole, as evidenced by the stellar cluster that is presently located at the CND's centre. In this paper, we report the results of a computational study of the dynamics of the CND. The results lead us to question two paradigms that are prevalent in previous research on the Galactic Centre. The first is that the disc's inner cavity is maintained by the interaction of the central stellar cluster's strong winds with the disc's inner rim, and secondly, that the presence of unstable clumps in the disc implies that the CND is a transient feature. Our simulations show that, in the absence of a magnetic field, the interaction of the wind with the inner disc rim actually leads to a filling of the inner cavity within a few orbital time-scales, contrary to previous expectations. However, including the effects of magnetic fields stabilizes the inner disc rim against rapid inward migration. Furthermore, this interaction causes instabilities that continuously create clumps that are individually unstable against tidal shearing. Thus the occurrence of such unstable clumps does not necessarily mean that the disc is itself a transient phenomenon. The next steps in this investigation are to explore the effect of the magnetorotational instability on the disc evolution and to test whether the results presented here persist for longer time-scales than those considered here.

By virtue of its proximity, the Virgo Cluster is an ideal laboratory for us to test our understanding of the formation of structure in our Universe. In this spirit, we present a dynamical study of 33 gas-poor and 34 gas-rich Virgo galaxies as part of the Spectroscopic and H-band Imaging of Virgo survey. Our final spectroscopic data set was acquired at the 3.5-m telescope at the Apache Point Observatory. Hα rotation curves for the gas-rich galaxies were modelled with a multi-parameter fit function from which various velocity measurements were inferred. Analog values were measured off of the observed rotation curves, but yielded noisier scaling relations, such as the luminosity-velocity relation (also known as the Tully-Fisher relation). Our best i-band Tully-Fisher relation has slope α=-7.2 ± 0.5 and intercept M_i(2.3)=-21.5 ± 1.1 mag, matching similar previous studies. Our study takes advantage of our own, as well as literature, data; we plan to continue expanding our compilation in order to build the largest Tully-Fisher relation for a cluster to date. Following extensive testing of the IDL routine pPXF, extended velocity dispersion profiles were extracted for our gas-poor galaxies. Considering the lack of a common standard for the measurement of a fiducial galaxy velocity dispersion in the literature, we have endeavoured to rectify this situation by determining the radius at which the measured velocity dispersion, coupled with the galaxy luminosity, yields the tightest Faber-Jackson relation. We found that radius to be 1.5 R_e, which exceeds the extent of most dispersion profiles in other works. The slope of our Faber-Jackson relation is α=-4.3 ± 0.2, which closely matches the virial value of 4. This analysis will soon be applied to a study of the Virgo Cluster Fundamental Plane. Rotation correction of our dispersion profiles will also permit the study of galaxies' velocity dispersion profile shapes in an attempt to refine our understanding of the overall manifold of galaxy structural parameters. / Thesis (Master, Physics, Engineering Physics and Astronomy) -- Queen's University, 2012-12-22 19:09:06.192