Philosophiae Doctor - PhD / There have been a number of attempts to measure the expansion rate of the Universe using age-dating of Luminous Red Galaxies (LRGs). Assuming that stars in LRGs form at the same time, age-dating of two populations of LRGs at different redshifts can provide an estimate of the time different associated with the corresponding redshift interval (dz/dt). This gives a direct estimate of the Hubble parameter H (z) at the average redshift of the two populations. In this thesis, we explore the validity of this method by using two different sets of data. Firstly, we select a homogeneous sample of passively evolving galaxies over 0.10 < z < 0.40 from the Sloan Digital Sky Survey Data Release Seven (SDSS-DR7) catalogue by applying a refined criteria, which is based on absolute magnitude. Secondly, we carry out series of observations on the Southern African Large Telescope (SALT) to obtain spectra of LRGs at two narrow redshift ranges z ' 0.40 and z ' 0.55 in order to calculate the Hubble parameter H(z) at z ' 0.47. We utilise two distinct methods of age-dating including the use of absorption Lick index lines and full spectral fitting on high signal-to-noise galaxy spectra from our sample. By establishing the age-redshift relation of the quiescent, passively evolving galaxies from SDSS, we obtain three improved new observational H(z) data points which are H(z) = 76.8 5.3 km s􀀀1Mpc􀀀1 at z ' 0.28, H(z) = 78.5 6.8 km s􀀀1Mpc􀀀1 at z ' 0.30 and H(z) = 86.3 7.6 km s􀀀1Mpc􀀀1 at z ' 0.32 respectively. We also find another H(z) value of 105 39 km s􀀀1Mpc􀀀1 at z ' 0.47 when age-dating LRGs observed with SALT. Combining all 4 data points with another 25 data points in the literature, we place better constraints on cosmological models and find the matter density parameter to be constrained by m = 0:32+0:05 􀀀0:06 and the Hubble constant to be H0 =68.5 2.4. These results are very consistent with other studies. Through this work, we are able to demonstrate that the cosmic chronometers approach can potentially be used to explore the evolution of the Universe.

>Magister Scientiae - MSc / The radio emission of radio-quiet active galactic nuclei (AGN) is thought to be from star formation and AGN related emission. I investigate these sources using 1.4 GHz radio data from FIRST and three optical quasars samples from the SDSS: (i) a volume-limited sample in the redshift range 0:2 < z < 0:4 defined by Mi < -23 (ii) magnitude-limited sample in the redshift range 1:8 < z < 2:5 defined by mr ≤ 18:5 and (iii) a uniform sample in the redshift range 0:2 < z < 3:5 (divided into 12 redshift bins). I constructed radio source counts and radio luminosity functions (RLFs) using the optical quasars detected in FIRST, which are consistent with literature results obtained using SDSS and NVSS quasars. There are differences at the low uxs end because of the different resolutions of FIRST and NVSS. I applied a median stack method to the 12 redshift bins of the uniform sample and found that the median ux decreases from 182 µJy in the lowest redshift bin to 39 µJy and the highest redshift bin. This is because the high redshift quasars although more luminous than their low redshift counterparts, they are much further away so they have lower uxes. I probed the quasar radio source counts to lower levels using reconstructed source counts obtained by applying the Bayesian stack technique. The reconstructed radio source counts were then used to constructed the quasar RLF to lower levels, where I found: (i) for z < 1 the constructed quasar RLF has the same slope as the detected quasars, suggesting that like the detect quasars their radio emission is dominated by AGN related emission (ii) above z = 1 the constructed RLF steepens with redshift, which suggests the strong link between accretion rate and radio jet power is gradually breaking down towards faint optical luminosities at high redshift. / National Astrophysics and Space Science Program (NASSP) and SKA Africa

The increasing importance of narrow-band radiations is traced in the recent history of radio astronomy. The need for multi-channel spectrometers to observe these radiations is stressed. The theoretical basis of spectral analysis is given with particular emphasis on autocorrelation or interference methods. A twenty-channel radio-frequency spectrometer designed on interference principles has been constructed and found to perform in accordance with its theory of operation. When used in conjunction with a 25-metre telescope and a hydrogen receiver the spectrometer is capable of producing low-noise wideband spectra at high speed. The spectrometer output was recorded on punched cards, and subsequent data processing was by digital methods. A large area including the position of the spiral galaxy M31 was surveyed with the help of the spectrometer. One hundred and forty-three independent spectra of the 21-cm radiation of atomic hydrogen were obtained and are analyzed in terms of area, velocity, and shape. The major axis of the nebula is found to extend about 2.5° either side of the centre, in agreement with the work of van de Hulst, Raimond, and van Woerden (1957). The length of the minor axis, after correction for the effect of the antenna beamwidth, is only 40', a result which indicates a reduction in the inclination (of the plane of the galaxy to the line of sight) from 14.5° to 8.2°. This lower value leads to an upward revision of the optical axial ratio (of galactic thickness to galactic diameter) to 0.2, while maintaining a low ratio (0.07, Schmidt, 1957) for the distribution of atomic hydrogen. A high axial ratio would clear the way for a reinterpretation of the optical velocities of emission nebulae in M31 (Mayall, 1950), which have so far appeared to be in violent contradiction to the radio velocities (van de Hulst et al, 1957). It is suggested that many of these emission objects may lie some distance from the plane of the galaxy. The position angle of M31, as revealed by the spectrometer observations is distinctly less than the 38° established optically. A new value of 33° is proposed and it is suggested that the former value can be accounted for in terms of an increased axial ratio and the observed asymmetries in the light distribution. The velocity of the centre of gravity of M31 has been obtained by summation of all 143 spectra. The result, -295.6±0.4 km/sec with respect to the local standard of rest, is in complete agreement with that found by van de Hulst (ibid). Radial motions of a few km/sec are possible in the outer parts of M31 but their presence has not been established. Many of the spectra have multiple peaks, which may be interpreted in terms of spiral structure. The velocities of certain concentrations of atomic hydrogen are measurable but their positions are not resolved by the antenna beam. / Science, Faculty of / Physics and Astronomy, Department of / Graduate

京都大学 / 新制・課程博士 / 博士(理学) / 甲第23013号 / 理博第4690号 / 新制||理||1672(附属図書館) / 京都大学大学院理学研究科物理学・宇宙物理学専攻 / (主査)教授 太田 耕司, 教授 長田 哲也, 准教授 栗田 光樹夫 / 学位規則第4条第1項該当 / Doctor of Science / Kyoto University / DFAM

We use the APOSTLE simulation suite to study the formation of galactic disks, in order to better understand the origin of their vertical structure. We select a disk-dominated Milky Way analogue galaxy from the simulation which experiences a minimum of external interaction with its environment as a generalizable test case. The simulated stellar disk is found to form upside-down from a gradually thinning, flared gaseous disk, where the rate of thinning is regulated by feedback from in-situ star formation. No significant sources of vertical heating are present in the disk, allowing the vertical structure of newly-formed stellar populations to be preserved over time. As a result, the properties of the stellar disk as a function of age accurately trace the properties of the gaseous disk as a function of time. This allows us to derive a physical model, in which the disk is isothermal, in quasi-hydrostatic equilibrium, and vertically supported by bulk motions rather than thermal pressure, which relates the present-day vertical age-velocity dispersion relation (AVR) at a given radius to the local star formation history as a simple power-law relation, with a best fit power law index $n=1.82$. This relation is then applied to the observed AVRs in the Milky Way from the recent literature, providing a predicted local star formation history for the Milky Way as a function of radius. We then compare this predicted history to others from the literature, in order to test whether our upside-down model from the simulation is consistent with the observed Galaxy. We also examine the observed ratio of vertical to radial velocity dispersions for consistency with our model. While our predicted history is broadly consistent with other predictions, the range of possible histories in the literature makes a more definitive conclusion difficult. / Graduate

Dwarf galaxies may form in the tidal tails of galaxy interactions. If these tidal dwarf galaxies (TDGs) detach from their parent galaxies, then an independent dwarf galaxy emerges. However, the lifespan of such objects is uncertain. Using IR, UV, and optical images, we conducted a search for detached TDGs from a set of 40 interacting galaxy pairs in the local Universe, and a control sample of 37 spiral galaxies. Both samples include 3.6 micron, 4.5 micron, 8 micron, and NUV images. In an earlier study (Smith et al. 2016), we used the IRAF daofind software (Stetson 1987) to search for star-forming regions within the main bodies of these galaxies and in their extended tidal tails. In the current study, we used the same procedure to search for such regions outside of the galaxies. We used two spatial scales to search for the TDGs, 1 kiloparsec and 2.5 kiloparsecs radius, and then used Spitzer infrared colors to identify and eliminate possible foreground stars and background quasars. The remaining objects may be detached tidal dwarfs that formed in the tails and then escaped. After comparing our observational results of the number of TDGs surrounding our interacting galaxies to the numbers around normal spirals, we find no significant difference in the number of candidate TDGs near interacting galaxy pairs compared to normal spiral galaxies. The most promising TDG candidates will be targeted by follow-up spectroscopic observations to determine their redshifts, metallicities, and their velocity structures. Younger TDGs are expected to have higher metallicities relative to their masses compared to primordial dwarf galaxies, relative to the standard mass-luminosity relationship for galaxies. Furthermore, TDGs should lack dark matter in contrast to primordial dwarf galaxies.

>Magister Scientiae - MSc / This work aims to study the dark matter content of the nearby (7.38 Mpc) dwarf galaxy IC 4710 using the HI line observations from the Australia Telescope Compact Array (ATCA). We produce the rst interferometric maps of the galaxy HI distribution and dynamics and use these maps to measure important quantities such as total HI mass, velocity width, and size. We create a dynamical model of the galaxy using a three-dimensional modeling technique. The rotation curve was obtained by tting a 3D tilted ring model to the HI data cube of galaxy IC 4710. The dynamical modeling of IC 4710 is being done for the rst time. We compare the model to the data cube to check for accuracy and found that they are in good agreement; this shows that the results are reliable. The obtained rotation curve is rising steeply until it reaches the maximum rotation velocity of 24.6 km s􀀀1 at a radius of 100 arcsec.

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.

In this dissertation work we sought to answer questions about the age, composition, and origin of planetary bodies. We implemented multiple approaches to answer these questions. To determine the age of the Clarissa asteroid family we implemented a modified version of SWIFT: a Solar System integration software package by Levison & Duncan (1994) to account for gravitational as well as thermal perturbations. This work constrained the age of the Clarissa asteroid family to be 56 ± 6 My. Next, we used a sum to one constraint weighted least squares (STO WLS) modeling approach to model thermal infrared (TIR) spectra of a suite of primitive asteroid analogs spectrally and volumetrically dominated by fine particulates ( < 38 µm). We determined that an alternative approach to the STO WLS model is needed to analyze asteroid regolith when it is dominated by fine particles ( < 90 µm). Our next approach included the Trojan asteroids (911) Agamemnon, (1172) Aneas, and (624) Hektor, and primitive asteroid (944) Hidalgo whose emissivity spectra share a prominent 10 µm plateau that is also present in cometary comae spectra. We used Multiple Sphere T-Matrix (MSTM) and Hapke reflectance models to model the asteroid spectral features using a mixture of olivine components (Mg-rich and Fe-rich olivine), fine particles (~0.5-1.0 µm), and lunar-like porosities (~74-87%). Finally, we used a light scattering Mie and Monte Carlo radiative transfer approach to model ambient (measured under Earth-like conditions) lunar regolith spectra. This study indicates that additional work needs to be done to develop an integrated thermal and light-scattering model that can replicate the effects of the thermal gradient present under lunar environment conditions because a light-scattering model alone is not able to reproduce the observed changes in the spectra that we see with space weathering.