We continue to build support for the proposal to use H II galaxies (HIIGx) and giant extragalactic H II regions (GEHR) as standard candles to construct the Hubble diagram at redshifts beyond the current reach of Type Ia supernovae. Using a sample of 25 high-redshift HIIGx, 107 local HIIGx, and 24 GEHR, we confirm that the correlation between the emission -line luminosity and ionized -gas velocity dispersion is a viable luminosity indicator, and use it to test and compare the standard model Lambda CDM and the R-h = ct universe by optimizing the parameters in each cosmology using a maximization of the likelihood function. For the flat Lambda CDM model, the best fit is obtained with Omega(m) = 0.40(-0.09)(+0.09). However, statistical tools, such as the Akaike (AIC), Kullback (KIC) and Bayes (BIC) Information Criteria favour R-h = Ct over the standard model with a likelihood of approximate to 94.8-98.8 per cent versus only per cent. For wCDM (the version of ACDM with a dark -energy equation of state wde = Pde/Pde rather than was t WA = 1), a statistically acceptable fit is realized with Omega(m) = 0.221(-0.14)(+0.16) and wde = 0.511'0'21-5" which, however, are not fully consistent with their concordance values. In this case, wCDM has two more free parameters than R-h = Ct, and is penalized more heavily by these criteria. We find that R-h = Ct is strongly favoured over wCDM with a likelihood of approximate to 92.9-99.6 per cent versus only 0.4-7.1 per cent. The current HIIGx sample is already large enough for the BIC to rule out ACDM/wCDM in favour of R-h = Ct at a confidence level approaching 3 sigma.

Um dos maiores desafios atuais da cosmologia é entender a natureza da energia escura. Esse trabalho busca usar os dados das distâncias de supernovas do tipo 1a, da idade de galáxias com população estelar muito antiga, das oscilações acústicas de bárions e das anisotropias da radiação cósmica de fundo para encontrar através do método de Monte Carlo em cadeias de Markov os parâmetros livres de uma possível equação de estado para a energia escura (w(z)) em redshift 0 < z < 2000. Entretanto esse trabalho não encontrou nenhum tipo de diferença significativa entre a equação de estado proposta e w = -1 dentro do intervalo de redshift estudado. / One of the current major challenges of cosmology is understand the nature of the dark energy. This work uses the data from supernovas type 1a, galaxies with old stellar populations, baryonic accustic oscilations and anisotropy of the cosmic microwave background to find through the Markov chains Monte Carlo method the free parameters of a possible equations of state for dark energy (w(z)) on redshift 0 < z < 2000. However, this work did not find any type of significant difference between the equation of state suggested and w = -1 inside the interval of redshift studied.

Weak gravitational lensing has developed to be one of the most powerful tools for studying the (dark) matter distribution in the Universe. Most weak lensing studies thus far were con- ducted in the optical and near infrared. Measuring weak lensing in the radio though, provided it is feasible, can be very advantageous. One can exploit the well known and deterministic beam pattern of a radio telescope and the polarisation information in radio data to reduce shape biases and intrinsic alignment effects respectively. Combining the information from an optical and a radio survey can also help remove systematics from both datasets. This has motivated this study that uses archival radio and optical data to treat telescope systematics and measure an unbiased weak lensing signal using shape information derived from radio observations. Using simulations I have shown that an unbiased convergence cross power spectrum can be measured in the presence of the large scale (θ > 1◦) systematics detected in FIRST and SDSS. The method however amplifies the uncertainties by a factor ∼2.5 compared to the errors due to cosmic variance and noise due to galaxy intrinsic shape alone. Using the shape information from the two surveys I measure a Ckappakappa spectrum signal that is inconsistent with zero at the 2.7sigma. The placed constraints are consistent with the expected signal in the concordance cosmological model assuming recent estimates of the cosmological parameters from the Planck satellite and literature values for the median redshifts of SDSS and FIRST.Through simulations I also show that I can successfully remove position based small scale systematics (θ5). Using the deconvolved information for the resolved sources I calculate a FWHM median size and flux density of 0.5'' and 300μJy respectively. Comparing the source number density and RMS noise of the study with those of FIRST, I extrapolate to predict that the number density of sources at > 5sigma will be ∼5arcmin-2, assuming the target noise threshold for the survey is reached.

Type Ia supernovae can be used as distance indicators for probing the expansion history of the Universe. The method has proved to be an efficient tool in cosmology and played a decisive role in the discovery of a yet unknown energy form, dark energy, that drives the accelerated expansion of the Universe. The work in this thesis addresses the nature of dark energy, both by presenting existing data, and by predicting opportunities and difficulties related to possible future data. Optical and infrared measurements of type Ia supernovae for different epochs in the cosmic expansion history are presented along with a discussion of the systematic errors. The data have been obtained with several instruments, and an optimal method for measuring the lightcurve of a background contaminated source has been used. The procedure was also tested by applying it on simulated images. The future of supernova cosmology, and the target precision of cosmological parameters for the proposed SNAP satellite are discussed. In particular, the limits that can be set on various dark energy scenarios are investigated. The possibility of distinguishing between different inverse power-law quintessence models is also studied. The predictions are based on calculations made with the Supernova Observation Calculator, a software package, introduced in the thesis, for simulating the light propagation from distant objects. This tool has also been used for investigating how SNAP observations could be biased by gravitational lensing, and to what extent this would affect cosmology fitting. An alternative approach for estimating cosmological parameters, where lensing effects are taken into account, is also suggested. Finally, it is investigated to what extent strongly lensed core-collapse supernovae could be used as an alternative approach for determining cosmological parameters.

Quasars at high redshift provide direct information on the mass growth of supermassive black holes (SMBHs) and, in turn, yield important clues about how the universe evolved since the first (Pop III) stars started forming. Yet even basic questions regarding the seeds of these objects and their growth mechanism remain unanswered. The anticipated launch of eROSITA and ATHENA is expected to facilitate observations of high-redshift quasars needed to resolve these issues. In this paper, we compare accretion-based SMBH growth in the concordance Lambda CDM model with that in the alternative Friedmann-Robertson-Walker cosmology known as the R-h = ct universe. Previous work has shown that the timeline predicted by the latter can account for the origin and growth of the greater than or similar to 10(9) M-circle dot highest redshift quasars better than that of the standard model. Here, we significantly advance this comparison by determining the soft X-ray flux that would be observed for Eddington-limited accretion growth as a function of redshift in both cosmologies. Our results indicate that a clear difference emerges between the two in terms of the number of detectable quasars at redshift z greater than or similar to 7, raising the expectation that the next decade will provide the observational data needed to discriminate between these two models based on the number of detected high-redshift quasar progenitors. For example, while the upcoming ATHENA mission is expected to detect similar to 0.16 (i.e., essentially zero) quasars at z similar to 7 in R-h = ct, it should detect similar to 160 in Lambda CDM-a quantitatively compelling difference.

Classical Cepheids form one of the foundations of modern cosmology and the extragalactic distance scale; however, cosmic microwave background observations measure cosmological parameters and indirectly the Hubble Constant, H 0, to unparalleled precision. The coming decade will provide opportunities to measure H0 to 2% uncertainty thanks to the Gaia satellite, JWST, ELTs and other telescopes using Cepheids and other standard candles. In this work, we discuss the upcoming role for variable stars and asteroseismology in calibrating the distance scale and measuring H0 and what problems exist in understanding these stars that will feed back on these measurements.

No description available.

Late-time cosmic acceleration is one of the most interesting unsolved puzzles in modern cosmology. The explanation most accepted nowadays, dark energy, raises questions about its own nature, e.g. what exactly is dark energy, and implications to the observations, e.g. how to handle fine tuning problem and coincidence problem. Hence, dark energy evolution through cosmic history, together with its equation of state, are subjects of research in many current experiments. In this dissertation, using Markov Chain Monte Carlo sampling, we try to constrain the evolution of the dark energy equation of state in a nearly model-independent approach by combining different datasets coming from observations of baryon acoustic oscillations, cosmic chronometers, cosmic microwave background anisotropies and type Ia supernovae. We found no strong evidence that could indicate deviations from LCDM model, which is the standard model in cosmology accepted today. / A aceleração cósmica atual é um dos mais interessantes enigmas não resolvidos da cosmologia moderna. A explicação mais aceita hoje em dia, a energia escura, levanta questões acerca de sua própria natureza, como o que é exatamente a energia escura, e as implicações para as observações, por exemplo como lidar com o problema do ajuste fino e o problema da coincidência. Por isso, a evolução da energia escura durante a história cósmica, juntamente com sua equação de estado, são objetos de pesquisa em inúmeros experimentos atuais. Nesta dissertação, usando amostragem por cadeias de Markov de Monte Carlo, tentamos restringir a evolução da equação de estado da energia escura em uma abordagem quase independente de modelo ao combinar diferentes conjuntos de dados provenientes de observações de oscilações acústicas de bárions, cronômetros cósmicos, anisotropias da radiação cósmica de fundo e supernovas tipo Ia. Não encontramos evidências fortes que pudessem indicar desvios do modelo LCDM, o qual é o modelo padrão aceito hoje na cosmologia.

Dans le modèle standard de cosmologie ΛCDM, environ 72% de la densité d'énergie totale de l'Univers se présente sous la forme d'énergie sombre qui causerait la présente accélération de l'Univers. Parmi les sondes cosmologiques couramment utilisées, l'effet de lentille gravitationnel forte dans les amas est une technique prometteuse fournissant des contraintes orthogonales sur les paramètres cosmologiques. Le programme HFF a permis une amélioration significative de l'estimation de la distribution de masse des amas. Cependant, la modélisation de l'effet de lentille forte dans les amas semble ne pas atteindre la résolution angulaire des observations HST. Cette thèse fournit une meilleure compréhension de l'impact des erreurs systématiques dans la modélisation paramétrique de l'effet de lentille forte dans les amas de galaxies et, donc, sur la détermination des paramètres cosmologiques. Premièrement, j'ai analysé deux amas de galaxies simulés, ayant les mêmes caractéristiques que les amas du programme HFF, Ares et Hera. J'ai utilisé plusieurs estimateurs afin d'évaluer la qualité de nos reconstructions obtenues, permettant de quantifier l'impact des erreurs systématiques dues, au choix des profils de densité et configurations et, ensuite, de la disponibilité d'images multiples dans la détermination de paramètres cosmologiques. Deuxièmement, en utilisant deux amas de galaxies, j'ai testé quatre modèles cosmologiques pour lesquels l'équation d'état de l'énergie sombre, w(z), est paramétrisée en fonction du redshift. J'ai réalisé plusieurs modélisations pour quantifier l'impact des erreurs systématiques liées à la position des images multiples sur les paramètres cosmologiques. / In the standard cosmological model ΛCDM, about 70% of the energy density of the Universe is in the form of a dark energy that would cause the current acceleration of the Universe. Among the extensively used cosmological probes, using strong lensing features in galaxy clusters is a promising technique yielding orthogonal constraints on cosmological parameters. The program HFF has led to a significant improvement of cluster mass estimates. However, strong lensing modelling appears to be still unable to match the HST observations angular resolution.This thesis provides a better understanding of how systematic errors impact the retrieval of cosmological parameters in order to use strong lensing clusters as reliable cosmological probes. Firstly, I have analyzed two simulated HFF-like clusters, Ares and Hera, I use several estimators to assess the goodness of our reconstructions by comparing our multiple models, with the input models. This allows to quantify the impact of systematic errors arising from the choice of different density profiles and configurations and, secondly, from the availability of constraints in the parametric modelling of strong lensing clusters and therefore on the retrieval of cosmological parameters. Secondly, I probe four cosmological models in which the equation of state of dark energy, w(z), is parameterized as a function of redshift using strong lensing features in two galaxy clusters. To quantify how the cosmological constraints are biased due to systematic effects in the strong lensing modelling, I carry out several modelling attempts considering different uncertainties for the multiple images positions.

Submitted by Emanuel Varela Cardoso (emanuel.varela@ufcg.edu.br) on 2018-10-16T19:37:30Z No. of bitstreams: 1 GIVAL PORDEUS DA SILVA NETO – DISSERTAÇÃO (PPGFísica) 2015.pdf: 4886479 bytes, checksum: 8589cc7f91d5dab59210f3bf9b9a3d97 (MD5) / Made available in DSpace on 2018-10-16T19:37:30Z (GMT). No. of bitstreams: 1 GIVAL PORDEUS DA SILVA NETO – DISSERTAÇÃO (PPGFísica) 2015.pdf: 4886479 bytes, checksum: 8589cc7f91d5dab59210f3bf9b9a3d97 (MD5) Previous issue date: 2015-05-08 / Capes / A constante de Hubble (H0) é considerada fundamental na cosmologia. Ela é crucial para qualquer modelo cosmológico moderno, pois está relacionada com diversas grandezas cosmológicas, portanto, é de extrema importância a determinação mais restritiva e acurada possível do seu valor. A mais recente estimativa de H0 a partir de métodos locais (z 1), H0 = 73:8 2; 4 kms􀀀1Mpc􀀀1, e a partir de redshifts muito altos (z ' 1070), H0 = 67; 3 1; 2 kms􀀀1Mpc􀀀1, são discrepantes em um nível de con fiança de 2; 4 . Dentro deste contexto, Lima e Cunha (LC), a m de lançar alguma luz sobre este problema, derivou uma nova determinação de H0 utilizando quatro testes cosmológicos em redshifts intermediários (z 1), com base no chamado modelo CDM Plano. Eles obtiveram H0 = 74; 1 2; 2 kms􀀀1Mpc􀀀1, em pleno acordo com as medições locais. Neste trabalho, exploramos a robustez do resultado de LC, procurando por erros sistemáticos e a sua dependência com o modelo cosmológico usado. Nós constatamos que o valor H0 a partir desta análise conjunta é muito fracamente dependente de modelos cosmológico, mas a morfologia adotada para inferir o raio central dos aglomerados de galáxias, altera o resultado, sendo a principal fonte de erros sistemáticos. Concluímos que uma melhor compreensão da morfologia dos aglomerados é fundamental para transformar esse método em um poderoso estimador de H0. / The Hubble constant (H0) is considered a fundamental constant of cosmology. It is crucial for any modern cosmological model, it is related to various cosmological quantities, so it is extremely important a restrictive and accurate determination of its value. The most recent estimate of H0 from local observations (z 1), H0 = 73:8 2; 4 kms􀀀�1Mpc􀀀�1, and from high redshifts (z ' 1070), H0 = 67; 3 1; 2 kms􀀀�1Mpc􀀀�1, are discrepant in a con dence level of 2; 4 . Within this context, Cunha and Lima (LC), in order to shed some light on this problem, derived a new determination of H0 using four cosmological tests at intermediate redshifts (z 1), based on the model called Flat CDM. They obtained H0 = 74; 1 2; 2 kms􀀀�1Mpc􀀀�1, in full agreement with local measurements. In this work, we explore the robustness of the result LC looking for systematic errors and its dependence on the cosmological model used. We found that the H0 value from this combined analysis is very weakly dependent on the underlying cosmological model, but the morphology adopted to infer the core radius of galaxy clusters, changes the estimates being the main source of systematic errors. Hence, we conclude that a better understanding of the morphology of the clusters is essential to transform this method in a powerful cross-check to H0.