Since the discovery that the large-scale dynamics of galaxy clusters are dominated by dark matter, cosmologists have aspired to measure the spatial distribution of dark matter and identify its nature. Gravitational lensing, especially employing the Hubble Space Telescope (HST) has emerged as the tool-of-choice for mapping dark matter. Standing on the shoulders of the pioneering 1990's, this thesis is the first homogeneous lensing study of clusters with HST. We measure the mass and structure of an objectively-selected sample of X-ray luminous clusters at a single epoch (z ~ 0.2). We present observations often clusters (L(_x)≥8x10(^44)[0.1=2.4 keV] ergs(^-1)) and use the numerous gravitationally-lensed features in these data to constrain a detailed model of the central regions (r ~ 500 kpc) of each cluster. Our models provide an unprecedented view of cluster morphology, revealing that 60% of the sample contain significant substructure. Chandra X-ray observations confirm this is a signature of dynamical immaturity, and show that the mean temperature of the intra-cluster medium of the morphologically complex clusters is ~ 25% higher than then regular siblings. This offset results in a critical, and previously unexplored, systematic uncertainty in the use of clusters to normalise the mass power spectrum. We also use the detailed morphology of the clusters to constrain the nature of dark matter. We then exploit the clusters as gravitational telescopes, using ground-based near-infrared imaging to construct a sample of 60 gravitationally magnified Extremely Red Objects (EROs), a population that is believed to harbour important clues on the formation epoch and mechanism of massive galaxies. This unique sample overcomes the faintness of EROs (R ≥ 23, K ≥ 18) to uncover a wealth of morphological, photometric and spectroscopic evidence of diversity in both passively evolving and dusty active EROs. Coupled with our deep number counts (to K ~ 22), these observations provide important new constraints on competing theoretical models of galaxy formation.

No description available.

We interpret distance measurements from nearby galaxies, type Ia supernovae, and gamma-ray bursts in the light of a cosmological model that incorporates a spatial averaging technique to account for the inhomogeneous distribution of structure in the late-epoch Universe and the consequent importance of the location of the observer. In the timescape cosmology it is suggested that dark energy is a misidentification of gravitational energy gradients---and consequently of the relative calibration of clocks and rulers---in a complex inhomogeneous structure. This model is consistent with the current supernova and gamma-ray burst data within the limits imposed by our understanding of the systematic uncertainties, to the extent that a Bayesian model comparison with the standard model yields a preference for the timescape model that is “not worth more than a bare mention”. In the spirit of the timescape model, of attempting to understand the astrophysics with as few cosmological assumptions as possible, we perform a model-independent analysis of galaxy distances in the local Universe. We find that the rest frame of the Local Group provides a more uniform Hubble expansion field than the rest frame of the CMB. We find that the dipole in the Hubble expansion field coincides with the dipole in the CMB temperature with a correlation coefficient of -0.92, and that this pattern is induced within 60 h⁻¹ Mpc, provided the variation in the distance-redshift relation due to the formation of structure is taken into account.

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.

La population de galaxies poussiéreuses ayant un fort taux de formation stellaire (Dusty Star Forming Galaxies, DSFGs) joue un rôle très important dans l’histoire de l’univers, avec des taux de formation d’étoiles allant de quelques centaines à quelques milliers de masses solaires par an. Les sondages infrarouges, comme ceux entrepris à l’aide du satellite Herschel, nous offrent l’opportunité de recenser de manière approfondie ces DSFGs jusqu’à de grands décalages spectraux. Cependant, jusqu’à présent seul un petit nombre de DSFG détecté par Herschel ont été confirmés pour être à des décalages spectraux supérieurs à 4. Les modèles de formation et d’évolution des galaxies stipulent généralement que la population de DSFG à z > 4 sont les progéniteurs des galaxies elliptiques, observées dans les amas les plus massifs de l’univers local. L’abondance des DSFGs à z > 4 se révèle donc être décisive pour contraindre ces modèles ainsi que pour vérifier notre compréhension globale de l’univers lointain. Le premier objectif de mon travail de recherche est d’identifier les candidates galaxies à z > 4 détectées sur des champs les plus larges possibles observés par Herschel et l’instrument SPIRE et d’examiner les propriétés statistiques de celles-ci. A cette fin, j’ai créé un nouvel algorithme de sélection dans le but d’augmenter substantiellement le nombre de candidates et de comprendre leur nature. / Over the last few decades, great progress has been made in our understanding of the star formation history of the Universe. With the discovery of distant, dusty star-forming galaxies (DSFGs) it has become apparent that observing at rest-frame UV and optical wavelengths is insufficient as a large fraction of the star formation is dust obscured. Thanks to the extensive observational studies carried out during the last two decades, we learn that DSFGs have a redshift peak at z ∼ 2, matching the cosmic time where galaxies have formed most of their young, massive stars. However, it remains extremely challenging to use the Herschel space observatory for identifying a tail extending towards much higher redshifts (z > 4). As a result, until recently only a small number of infrared-selected DSFGs at z > 4 were known, most of them strongly gravitationally lensed. One of the main goals of this Thesis is to assemble candidate z > 4 galaxies detected in a large area survey observed by Herschel-SPIRE and to examine the statistical properties and environments of these systems.

This DPhil dissertation presents two new and independent samples of faint radio sources. The first sample is the 37 SXDS radio sources with flux densities at 1.4-GHz above 2 mJy, a spectroscopic completeness of 65% and a median redshift z_med ≈ 1.1. The second sample is the 47 TOOT00 radio sources with flux densities at 151 MHz above 100 mJy, a spectroscopic completeness of 85% and z_med ∼ 1.25. Optical, near- and mid-IR photometry, optical spectroscopy, and radio observations are used in the analysis and comparison of the two samples. The quasar fraction in the TOOT00 radio sources is 0.13 < f_q < 0.25 above the FRI/FRII break in radio luminosity, while use of 24 μm data reveals objects with significant but sometimes obscured accretion and gives quasar-mode fraction of 0.5 → 0.9 above the FRI/FRII break. The FRI/FRII divide seen at z < ∼ 0.5 is also observed at z ∼ 1 for FRII objects in the TOOT00 and SXDS samples, but examples of FRI radio sources above the FRI/FRII break do exist. The total number of the TOOT00 objects and their distribution are consistent with simulations based on extrapolations from previous work, while for the SXDS objects the results are only broadly similar. Based on that comparison, the redshift spikes seen at z ∼ 1.3 in TOOT00 and at z ∼ 0.65 & 2.7 in SXDS appear to be significant, and might be due to Large-Scale Structure. A V/Vmax test suggests the cosmic evolution of the TOOT00 and SXDS samples, is different. The TOOT00 radio sources are 2-times more luminous in host-galaxy starlight than the SXDS radio sources. The almost proportionality between radio luminosity at 1.4 GHz and 24 μm luminosity suggests that L_rad traces accretion luminosity and L[OII] ∝ L_rad^0.7 may reflect imperfections in the L[OII]-accretion luminosity scaling. Mid-IR 24 μm observations in the SXDS sample suggest that 30% of the light from the nucleus is absorbed by the torus and re-emitted in the mid-IR, while ∼ 1% of the light is scattered above and below the torus.

An extensive survey of extragalactic objects with accurate distances is difficult to perform. Distance at that scale is commonly found with redshift and most easily identified with spectroscopic observations, which are time intensive. This is especially a concern when surveying for the elusive, possibly non-existent dwarf galaxies in the centers of voids, whose light would be so faint that a spectroscopic survey to find them would be unreasonably time consuming. Photometric methods to calculate redshift could provide a much quicker way to find distance, but the photometric methods used thus far are characterized by large errors that make them unusable for research on nearby voids. I have been testing two photometric redshift methods that have been recently developed: the Gaussian filter method and the ramp filters method. The Gaussian filter method isolates objects that have emission within the bandpass of the Gaussian filters. Spectroscopic follow-up observations of objects observed with the Gaussian filter method confirmed that 41.9% of the objects identified by the method actually had emission lines within the bandpass of the filters, which is more than a random sampling where only 7% of galaxies had emission within that wavelength range. Assuming that all the lines identified were Hα, the photometric redshift calculated from the Gaussian filter observations had an error of 945 km/s (or 430 km/s by excluding one outlier). Ramp filter observations of objects with SDSS redshifts provided a way to identify redshift with an error of 641.8 km/s. These errors are about an order of magnitude less than other redshift methods. These methods show promise for uses in observational cosmology, specifically extragalactic survey work and searching for void galaxies.

No description available.

The inflationary ΛCDM cosmology currently provides an accurate description of the Universe. It has been tested using several observational techniques over a wide redshift range, and it provides a good fit to most of them. In addition, it is a surprisingly economical model, requiring only six parameters to characterize the background cosmology and its fluctuations. In this model, the Universe is dominated by a cosmological constant Λ driving an accelerated expansion, and by cold dark matter. The strongest constraints on parameters to date come from observations of the temperature and polarization anisotropies of the cosmic microwave background measured by the Planck satellite. There are, however, indications of features in the Planck power spectra, possible differences with high redshift ground-based CMB experiments, and 'tensions' between Planck and low redshift measurements of the Hubble constant and weak gravitational lensing. In this thesis, we review possible tensions and extensions to the Planck cosmology, at both high and low redshifts. We begin with the high redshift analysis, using the Planck data to test models which introduce oscillatory features in the primordial power spectrum. We also study possible departures from slow roll inflation using the generalized slow-roll formalism, which allows for order unity deviations. Although we find models which give marginal improvements on the temperature or polarization power spectra, the combination of temperature and polarization is found to be consistent with a featureless power-law primordial spectrum. We then focus on measurements of the polarized CMB sky by the South Pole Telescope collaboration, who report tension between their measurements and the ΛCDM cosmology and with the cosmological parameters determined by Planck. We find evidence of a high χ2 in the SPTpol spectra which is unlikely to be cosmological. We report consistency between the Planck and SPTpol polarization spectra over the multipoles accessible to Planck (l ∼< 1500). We then investigate tension at low redshifts. We begin with weak gravitational lensing in which a number of surveys have suggested that the amplitude of the fluctuation spectra is lower than the Planck value. We review the small-angle approximations commonly used in galaxy weak lensing analyses and their effect on cosmological parameters. We find that these approximations are perfectly adequate for present and near future experiments. We find internal inconsistencies in the recent KiDS-450 analysis involving photometric redshifts and the KiDS covariance matrix at large scales. Finally, we investigate the difference between measurements of the present day expansion rate of the Universe. We apply a novel parameterization of the inverse distance ladder to determine the present date value of the Hubble parameter H0, which assumes General Relativity but makes no further assumptions about systematic errors or the nature of dark energy. Our analysis uses baryon acoustic oscillation data and Type Ia Supernovae to constrain the expansion history assuming a value of the sound horizon determined from the CMB. Our results are in tension with recent direct determinations of H0. We conclude that this tension, if real, cannot be solved by modifications of the ΛCDM model at late times. Instead, we would require a modification of the theory at early times which reduces the sound horizon. We conclude that at this time there is no compelling evidence that conflicts with the ΛCDM cosmology either at low or at high redshifts.

京都大学 / 0048 / 新制・課程博士 / 博士(理学) / 甲第20908号 / 理博第4360号 / 新制||理||1626(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)准教授 樽家 篤史, 教授 佐々木 節, 教授 川合 光 / 学位規則第4条第1項該当 / Doctor of Science / Kyoto University / DFAM