Type Ia supernovae (SNe Ia) have proven to be extremely useful for measuring cosmological distances and were used for the discovery of the accelerated expansion of the universe. Although thousands of SNe Ia have been observed to date, many questions surrounding the physics of the explosions and the nature of their progenitor systems remain unanswered. An notable property of many SNe Ia is the relation between extinction due to dust and their colour. For example SN 2014J, the nearest SN Ia in recent years, has an extinction relation which would be very unusual to observe in the Milky Way. One possible explanation to the peculiar extinction could be the presence of circumstellar (CS) dust surrounding the explosions. Incidentally, some proposed progenitor models of SNe Ia suggest that the explosions are surrounded by shells of matter, which could account for the unusual extinction. CS gas would be ionised, if it is exposed to the intense ultraviolet (UV) radiation of a SN Ia. The research presented in this thesis focuses on the search for CS gas by observing the effects of photoionisation on absorption lines commonly detected in optical spectra. Simple models suggest that the frequently studied sodium doublet (Na I D) should significantly decrease or even disappear if the gas is in the CS environment. Conversely, the absence of variations implies that the absorbing gas clouds must be far from the explosion, in the interstellar medium (ISM). To date, few SNe Ia have been shown to have variable absorption lines, to which we have added another case with SN 2013gh. Yet, we have also shown that most observations searching for variable absorption lines have been taken at too late phases, when most CS gas will have already been ionised. Setting out to obtain the earliest possible coverage of a SN Ia with high-resolution spectra, we have been able to set strong limits on the presence of CS gas surrounding SN 2017cbv. Along with evidence from other observational methods, these results have shown that there is little matter in the CS environments of SNe Ia, suggesting that the peculiar extinction likely results from the dust properties of their host galaxy ISM. Although the progenitor question cannot be resolved by these observations, nondetections of CS gas point to models which do not deposit large amounts of matter in their surroundings. / <p>At the time of the doctoral defense, the following paper was unpublished and had a status as follows: Paper 5: Submitted.</p>

The use of Type Ia supernovae (SNe Ia) as distance indicators is essential for studying the expansion history of the Universe and for exploring the nature of dark energy. However, a lack of understanding of the progenitor systems and the empirically derived colour-brightness corrections represent severe limitations for SNe Ia as cosmological probes. In this thesis, we study how dust along the line of sight towards SNe Ia affects the observed light over a wide range of wavelengths; from X-rays to infrared. Unless properly corrected for, the existence of intergalactic dust will introduce a redshift dependent magnitude offset to standard candle sources and bias the cosmological parameter estimates as derived from observations of SNe Ia. We model the optical extinction and X-ray scattering properties of intergalactic dust grains to constrain the intergalactic opacity using a combined analysis of observed quasar colours and measurements of the soft X-ray background. We place upper limits on the extinction AB(z = 1) &lt; 0.10 - 0.25 mag, and the dust density parameter Ωdust &lt; 10−5 − 10−4 (ρgrain/3 g cm−3), for models with RV &lt; 12 − ∞, respectively. Dust in the host galaxies, and dust that may reside in the circumstellar (CS) environment, have important implications for the observed colours of SNe Ia. Using the Hubble Space Telescope and several ground based telescopes, we measure the extinction law, from UV to NIR, for a sample of six nearby SNe Ia. The SNe span a range of E(B − V ) ≈ 0.1 − 1.4 mag and RV  ≈ 1.5 − 2.7, showing a diversity of dust extinction parameters. We present mid- and far-infrared (IR) observations for a number of SNe Ia, obtained with the Herschel Space Observatory and Spitzer Space Telescope, addressing CS dust as an explanation for “peculiar” extinction towards some SNe Ia. No excess IR emission is detected, limiting CS dust masses, Mdust &lt; 10−5 solar masses. In particular, the timely appearance of SN 2014J in M82 - the closest SN Ia in several decades - allows for detailed studies, across an unprecedented wavelength range, of its lightcurve and spectral evolution along with the host galaxy and CS environment. / <p>At the time of the doctoral defense, the following papers were unpublished and had a status as follows: Paper 5: Manuscript. Paper 6: Manuscript.</p>

Measurements of the Hubble constantH(z) are increasingly being used to test the expansion rate predicted by various cosmological models. But the recent application of two-point diagnostics, such as Om(zi, zj) and Omh(2)(zi, zj), has produced considerable tension between Lambda CDM's predictions and several observations, with other models faring even worse. Part of this problem is attributable to the continued mixing of truly model-independent measurements using the cosmic-chronometer approach, and model-dependent data extracted from baryon acoustic oscillations. In this paper, we advance the use of two-point diagnostics beyond their current status, and introduce new variations, which we call Delta h(zi, zj), that are more useful for model comparisons. But we restrict our analysis exclusively to cosmic-chronometer data, which are truly model independent. Even for these measurements, however, we confirm the conclusions drawn by earlier workers that the data have strongly non-Gaussian uncertainties, requiring the use of both 'median' and 'mean' statistical approaches. Our results reveal that previous analyses using two-point diagnostics greatly underestimated the errors, thereby misinterpreting the level of tension between theoretical predictions and H(z) data. Instead, we demonstrate that as of today, only Einstein-de Sitter is ruled out by the two-point diagnostics at a level of significance exceeding similar to 3s. The R-h = ct universe is slightly favoured over the remaining models, including Lambda cold dark matter and Chevalier-Polarski-Linder, though all of them (other than Einstein-de Sitter) are consistent to within 1 sigma with the measured mean of the Delta h(zi, zj) diagnostics.

No description available.

L'âge des galaxies est un paramètre crucial dans le cadre des modèles de formation et d'évolution des galaxies. Ma thèse se base sur l'étude de cette quantité physique dans le cadre du sondage profond de VIMOS (VUDS). Ce sondage permet d'étudier les galaxies dans l'univers jeune et de remonter au moment où il était agé de seulement quelques centaines de millions d'années. Durant ce doctorat, j'ai pu prendre part au traitement des données de ce sondage et j'ai été responsable de l'ensemble de la correction des spectres du sondage. J'ai également modifié et amélioré le logiciel GOSSIP qui est un logiciel d'ajustement de modèle de galaxie permettant d'extraire les paramètres physiques des galaxies. L'utilisation de ce logiciel m'a permis d'étudier l'extinction par le milieu intergalactique des galaxies ainsi que leurs âges. Ceci m'a permis d'étudier l'époque de formation des galaxies ainsi que l'évolution du paramètre de Hubble. / Age of galaxie is a crucial parameter in the framework of galaxy formation and evolution. This thesis is based on the study of this parameter in the framework of the VIMOS Ultra Deep Survey. This galaxy survey allows to study galaxies when the universe was young and to go back when it was few hundreads of million years old. During this PhD I could take part of the data processing and I was responsible of all the spectroscopic corrections. I also implemented and improved the GOSSIP software. This software is a template fitting program that allows the extraction of galaxy physical parameters. The use of this software allowed me to study the extinction of the Inter Galactic medium (IGM) as well as their ages. I could then study the epoch of galaxy formation and the evolution of the Hubble parameter

Nesta dissertação, uma revisão dos modelos cosmológicos newtonianos e neo-newtonianos baseados na formulação da hidrodinâmica clássica é apresentada, com especial ênfase para os resultados básicos e as limitações mais importantes dessas abordagens. Em seguida, mostramos que a descrição Lagrangiana clássica proposta por Lima, Moreira e Santos (1998) para fluidos simples, pode ser generalizada para incluir modelos com misturas de fluidos, e portanto, cosmologias mais realísticas contendo bárions, matéria escura e energia escura, bem como qualquer forma de interação entre essas componentes. Neste trabalho propomos uma descrição lagrangiana clássica para modelos relativísticos do tipo FRW. Nesta descrição, o comportamento dinâmico do fator de escala a(t), como previsto pelas cosmologias relativísticas, é substituído pelo movimento unidimensional de uma partícula teste de massa m sob a ação de um potencial clássico, V(x), onde x é a coordenada unidimensional da partícula. O tratamento pode ser aplicado para os mais diversos cenários de energia escura. Para exemplificar, discutimos com detalhe os seguintes modelos contendo matéria escura e energia escura: XCDM, X(z)CDM, Lambda CDM, Lambda(t) e gás de Chaplygin. Por completeza, modelos multidimensionais do tipo FRW também são considerados. Em todos esses modelos, o parâmetro de curvatura k das seções espaciais das cosmologias determina a energia total da partícula teste pela relação, E=-mk/2, tal como ocorre nos modelos de fluidos simples. As propriedades dinâmicas associadas com o presente estágio de aceleração do universo são univocamente descritas em termos da função potencial do sistema. Finalmente, utilizando os dados da distância de luminosidade provenientes das supernovas do tipo Ia, discutimos como o potencial unidimensional pode ser reconstruído a partir das observações. / In this dissertation, a review of the Newtonian and neo-Newtonian cosmological models based on the classical hydrodynamics formulation is presented with special emphasis to the basic results and the main limitations of such approaches. Next, we show that the classical Lagrangian description as proposed by Lima, Moreira & Santos (1998) for simple fluids, can be generalized to include fluid mixtures, and, therefore, more realistic cosmologies containing baryons, dark matter and dark energy, as well as, any kind of interaction among such components. In the lagrangian description, the dynamic behavior of the scale factor a(t), as predicted by the relativistic cosmologies, is replaced by the unidimensional motion of a test particle with mass m under the action of a classical potential, V(x), where x(t) is the coordinate of the particle. The treatment can be applied for many different scenarios of dark energy. In order to exemplify, we discuss with detail the following models containing dark matter and dark energy: XCDM, X(z)CDM, Lambda(t)CDM and the Chaplygin gas. For completeness, FRW type multidimensional models are also considered. For all these models, the curvature parameter k of the spatial sections in the relativistic cosmologies determines the total energy by the relation, E=-mk/2, as occurs in the simple fluid models. The dynamic property associated with the present accelerating stage of the Universe are univocally described in terms of the potential function of the system. Finally, by using the data from luminosity distance of supernovae type Ia, we discuss how the unidimensional potential can be reconstructed from the observations.

For this project, a historical statistical analysis of the Amplitude of Mass Fluctuations ($\sigma_8$) and Hubble's Constant ($H_0$) parameters in the Standard Cosmological Model was carried out to determine whether or not the given error bars truly represent the dispersion of values. It was found through analysis of the Chi-Squared ($\chi^2$) values of the data that for $\sigma_8$ (60 data points and $\chi^2$ between 183.167 and 189.037) that the associated probability Q is extremely low, with $Q = 1.5597*10^{-15}$ for the weighted average and $Q = 1.2107*10^{-14}$ for the best fit of the data. This was also the case for the $\chi^2$ values (163 data points and $\chi^2$ between 484.3977 and 575.655) of $H_0$, where $Q = 4.2176*10^{-34}$ for the linear fit of the data and $Q = 1.0342*10^{-47}$ for the weighted average of the data. Through further analysis, it is shown in question, a linear fit is a better estimate of the data than the weighted average. The general conclusion is that the statistical error bars have been underestimated (in around 20\% of the measurements), or the systematic errors were not properly taken into account.

The nature of existence, which science seeks to investigate, is dynamic as novel discoveries are constantly presented. To explain such a dynamic existence, science itself needs to be dynamic. Methodological differentiation is one way in which science expresses dynamism. Such differentiation led to the theological and the natural sciences, and conflicting views regarding the nature of existence: the theological worldview versus the natural worldview. This study is a comparison of the conflicting worldviews of the theological and cosmological (natural worldview) theories of the beginning of existence. The study compares them in an attempt to redress the conflict and encourage dialogue between the two methods for a better representation of existence. The study exposes the limits of the theological and the natural worldviews. It proposes a relationship of dialogue between them so that they transcend their individual limits and are able to grow. Dialogue involves the interchange of ideas to broaden perspectives, which leads to growth. A relationship of dialogue emphasises similarities in presuppositions, methodology and content, and exploits these to attain a greater degree of certitude. Theology and natural science can be viewed analogically as two sides of the same coin, two aspects to one reality, that can collaborate, albeit independently, to reveal a broader view of reality. They can converse through dialogue, exchange ideas and share views, even though they remain methodologically exclusive, independent worldviews. Finally, dialogue involves a transformation of reason in that it expects theologians and natural scientists to change the way they view reality. If we were to transform our reasoning into something more complete, our worldview should represent a more complete representation of existence. This means that the theologian and the scientist can, occasionally, go beyond their scope and method and push their knowledge towards progress through dialogue. This makes “transformed reason” the method of dialogue, which redresses the conflict between theology and natural science and encourages interchange between them. / Inhlobo yobukhona, isayense edinga ukuphenyisisa ngakho, kuyashintshashintsha njengokutholwayo okusha okuhlala njalo kwethulwa. Ukuchaza lokhu kushintshashintsha okukhona, isayense ngokwayo idinga ukushintshashintsha ngokuhambisana nesimo. Umehluko wezindlela zokwenza ngenye yendlela lapho isayense ekhombisa khona ukushintshashintsha ngokuhambisana nesimo. Lo mehluko uholele abaholi bezenkolo kanye nabesayense yemvelo, kanye nemibono engqubuzanayo maqondana nenhlobo yobukhona; umbono ngezenkolo uma kuqhathaniswa nombono ngezemvelo. Lolu cwaningo luqhathanisa umbono ongqubuzanayo ngomhlaba ngenkolo kanye nekhosmoloji (indlela yokubuka izinto yemvelo), amathiyori okuqala kobukhona. Ucwaningo luqhathanisa lezi zinto ngemizamo yokubhekana nokungqubuzana kanye nokukhuthaza idayalogu phakathi kwezindlela ezimbili ukuze kube nokumeleka kahle kobukhona. Lolu cwaningo luveza izihibe ezikhona kwindlela yokubuka izinto yezenkolo kanye nezemvelo. Luphakamisa ubudlelwane bedayalogu phakathi kwazo, ukuze kweqiwe imingcele yazo zombili ngayinye kanye nokukhula. Idayalogu ibandakanya ukushintshana ngemibono ukunabisa indlela yokubuka izinto, okuholela ekukhuleni. Ubudlelwane bedayalogu bugcizelela ukufana kwezilinganiso (presuppositions), izindlela zokwenza kanye nengqikithi, kanye nokucwaninga lezi zinto ukufinyelela ezingeni elikhulu lokuqiniseka ngendlela izinto eziyikho. Imfundo ngenkolo kanye nesayense yemvelo kungabonwa njengokulandelanayo kwezinhlangothi ezimbili kwikhoyini eyodwa, izinto ezimbili kwimvelo eyodwa, kungahambisana,ngisho noma okunye kuzimele ngokwehlukile kokunye, kuveza umbono obanzi walokho isimo esiyikho. Kungakhulumisana ngedayalogu, ukushintshana ngemibono kanye nokwabelana ngemibono, ngisho noma izindlela zakho zokwenza zehlukile, imibono ngomhlaba kwehlujkile nokuzimela. Okokugcina, idayalogu ibandakanya ushintsho lwembangela ngoba kulindele ukuthi abezenkolo kanye nososayense bashintshe izindlela ababona ngaso lokho isimo esiyikho. Uma bekufanele siguqule indlela esibona ngayo iziimbangela ukuya kwinto ethile ephelele, indlela esibona ngayo umhlaba nayo kumele imele umfanekiso ophelele kakhulu ngobukhona. Lokhu kusho ukuthi abaholi bezenkolo kanye nososayense, bangathi ngezinye izikhathi, babuke ngaphezulu kwendlela abobona ngayo kanye nezindlela zokwenza, kanye nokududula ulwazi lwabo ukuthi luthuthuke ngedayalogu. Lokhu kwenza "imbangela eguqukile" ibe yindlela yokwenza idayalogu, okubhekana nokungqubuzana phakathi kwezenkolo kanye nesayense yemvelo kanye nokukhuthaza ukuxhumana phakathi kwazo. / Sebopeho sa boteng, seo mahlale a batlang ho se batlisisa, se ba matla ha ditshibollo tse ntjha di nehelanwa kgafetsa. Ho hlalosa boteng bo matla jwalo, mahlale ka boona a hloka ho ba matla. Phapang ya mekgwa ke tsela e nngwe eo mahlale a hlalosang matla ka yona. Phapang e jwalo e lebisitse ho thuto ya bodumedi le mahlale a tlhaho, le maikutlo a hanyetsanang mabapi le sebopeho sa boteng: dipono tsa lefatshe tsa thuto ya bodumedi kgahlanong le pono e akaretsang ya tlhaho. Phuputso ena ke papiso ya maikutlo a akaretsang a lwantshanang a dikgopolo tsa thuto ya bodumedi le dikgopolo tsa tshimoloho le ntlafatso ya bokahohle (pono e akaretsang ya tlhaho) tsa qaleho ya boteng. Phuputso ena e di bapisa ho leka ho lokisa kgohlano le ho kgothaletsa puisano dipakeng tsa mekgwa e mmedi bakeng sa boemedi bo betere ba boteng. Phuputso ena e pepesa ditekanyetso tsa maikutlo a akaretsang a thuto ya bodumedi le tlhaho. E kgothaletsa kamano ya puisano dipakeng tsa tsona e le hore di fete ditekanyetso tsa tsona ka bomong mme di tsebe ho hola. Puisano e kenyeletsa phapanyetsano ya mehopolo ho hodisa maikutlo, e leng se lebisang ho kgolo. Kamano ya puisano e totobatsa ho tshwana dikgakanyong, mokgweng le ho dikateng, mme e sebedisa tsena ho fihlella tekanyetso e kgolo ya ho nepahala. Thuto ya bodumedi le mahlale a tlhaho di ka tadingwa ka mokgwa o tshwanang e le mahlakore a mabedi a tjhelete e le nngwe ya tshepe, dikarolo tse pedi ho nnete e le nngwe, tse ka sebedisanang, leha di ikemetse, ho senola pono e pharalletseng ya nnete. Di ka sebedisana ka dipuisano, tsa fapanyetsana maikutlo le ho arolelana dipono, leha e le hore di dula e le dipono tse akaretsang tse ikemetseng, tse ikgethang mokgweng. Qetellong, puisano e kenyeletsa phetoho ya mabaka ka hore e lebelletse ditsebi tsa thuto ya bodumedi le boramahlale ba tlhaho ho fetola tsela eo ba tadimang nnete ka yona. Haeba re ne re ka fetola monahano wa rona hore e be ntho e nngwe e felletseng, pono ya rona e akaretsang e lokela ho emela setshwantsho se felletseng sa boteng. Sena se bolela hore setsebi sa thuto ya bodumedi le ramahlale, ka dinako tse ding, ba ka feta maemo le mokgwa wa bona mme ba sutumeletsa tsebo ya bona tswelopeleng ka puisano. Sena se etsa "lebaka le fetotsweng" mokgwa wa puisano, o rarollang kgohlano dipakeng tsa thuto ya bodumedi le mahlale a tlhaho le ho kgothaletsa phapanyetsano dipakeng tsa tsona. / Philosophy, Practical and Systematic Theology / M.A. (Philosophy)

The current cosmological paradigm of an accelerating cosmic expansion issupported by observations of Type Ia supernovae. However, the light emittedby these and other cosmological sources is not only redshifted by cosmicexpansion but will also interact with matter along the light path. Especiallyintergalactic dust can lead to additional reddening and dimming of distantsources due to light scattering or absorption. This yields systematiccontaminations to cosmological measurements. This project builds afoundation and some of the tools that will be used in a master’s thesis withthe aim of analysing the spatial distribution and the properties of this cosmicdust. While previous studies assumed cosmic dust to be homogeneouslydistributed, it is expected to follow the spatial distribution of galaxies fromwhich it was expelled. This project also starts to recreate previous models ofhomogeneous dust models and measurements which will be used the futuremaster’s thesis. An analysis of the methods and tools used, along with some ofthe dust properties, is also made in this project.

This thesis aims to give an introduction to quintessence models as well ascomparing those models with the currently accepted ΛCDM model. We willconsider quintessence in a spatially flat and isotropic Universe and useregular dynamical systems on a bounded three dimensional phase spacewhere we perform numerical calculations. This enables a globalunderstanding of these models and makes it possible to give thoroughdescriptions of the dynamics. We will discuss the three different types ofquintessence: Thawing, Scaling and Tracking quintessence and comparethem with the ΛCDM model. This thesis is based on several scientific papersand contains new numerical calculations and associated analysis. / Denna kandidatuppsats syfte är att ge en första inblick i kvintessens samtatt jämföra sådana modeller med den nuvarande accepterade ΛCDMmodellen. Vi studerar kvintessens i ett rumshomogent, isotropt och plantUniversum och använder reguljära dynamiska system i ett begränsattredimensionellt fasrum där vi utför numeriska beräkningar. Detta tillåter englobal undersökning av dessa modeller och gör det möjligt att noggrantbeskriva dynamiken. Vi diskuterar de tre olika typerna av kvintessens:”Thawing”, ”Scaling” och ”Tracking” kvintessens och jämför dessa medΛCDM modellen. Uppsatsen är baserad på flertalet vetenskapliga artiklaroch innehåller nya numeriska beräkningar med tillhörande analys.