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We use recently published redshift space distortion measurements of the cosmological growth rate, f sigma(8)(z), to examine whether the linear evolution of perturbations in the R-h = ct cosmology is consistent with the observed development of large-scale structure. We find that these observations favour R-h = ct over the version of Lambda cold dark matter (Lambda CDM) optimized with the joint analysis of Planck and linear growth rate data, particularly in the redshift range 0 < z < 1, where a significant curvature in the functional form of f sigma(8)(z) predicted by the standard model-but not by R-h = ct-is absent in the data. When Lambda CDM is optimized using solely the growth rate measurements; however, the two models fit the observations equally well though, in this case, the low-redshift measurements find a lower value for the fluctuation amplitude than is expected in Planck Lambda CDM. Our results strongly affirm the need for more precise measurements of f sigma(8)(z) at all redshifts, but especially at z < 1.

Many measurements in cosmology depend on the use of integrated distances or time, but. galaxies evolving passively on a timescale much longer than their age difference allow us to determine the expansion rate H(z) solely as a function of the redshift-time derivative dz/dt. These model-independent "cosmic chronometers" can therefore be powerful discriminators for testing different cosmologies. In previous applications, the available sources strongly disfavored models (such as Lambda CDM) predicting a variable acceleration, preferring instead a steady expansion rate over the redshift range 0 less than or similar to z less than or similar to 2. A more recent catalog of 30 objects appears to suggest non-steady expansion. In this paper, we show that such a result is entirely due to the inclusion of a high, locally inferred value of the Hubble constant H-0 as an additional datum in a set of otherwise pure cosmic-chronometer measurements. This H-0, however, is not the same as the background Hubble constant if the local expansion rate is influenced by a Hubble Bubble. Used on their own, the cosmic chronometers completely reverse this conclusion, favoring instead a constant expansion rate out to z similar to 2.

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.

>Magister Scientiae - MSc / In the standard (‘concordance’) model of Cosmology, there is a fundamental assumption that the Universe is statistically isotropic and homogeneous on large scales, known as the Cosmological Principle. The Cosmological Principle requires that the dipole anisotropy apparent in the CMB should also be observed in galaxy number counts if this signal occurs due to the aberration and Doppler effects from our peculiar motion. This thesis will investigate the accuracy with which the cosmic kinematic dipole can be determined by comparing real data from NRAO VLA Sky Survey (NVSS) catalog with the simulated sky maps following its specifications. The mock maps are generated using FLASK code which assumes a lognormal distribution for the radio count density field from z=0 to z =4 and taking as an entry an angular power spectrum from CAMB which assumed a flat ΛCDM cosmology and a redshift distribution. After analising the kinematic dipole, we turn to the analysis of statistical isotropy in the catalog. We used ANalysis Of Variance (ANOVA) test on patches in the sky of different radii as one of the statistical tools for the analysis. We found that as we go to a higher radius for the patches, we have a better agreement between the theory and the observation as expected. We also saw that the more we are rigorous on the rejection criteria, the smaller is the discrepancy between the observed and simulated number count distribution in the sky. We found an optimum choice of 25◦ as patch size, and if the accepted patches have a maximum of 30% of their pixels masked. Therefore, we find that the NVSS data agrees with the fundamental assumption of statistical isotropy at angular scales > 20◦.

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.

Nos encontramos atualmente em um momento histórico privilegiado para a cosmologia. Na última década, o grande progresso das observações astronô- micas permitiu que diversos modelos cosmológicos pudessem ser testados com grande precisão. Com uma série de resultados observacionais sendo lançados, obtivemos informações valiosas sobre a expansão acelerada do universo primitivo e a expansão acelerada atual. Em sua essência, tais esforços observacionais buscam esclarecer algumas das questões mais fundamentais da cosmologia moderna, como a compreensão do mecanismo responsável pela aceleração do universo. Muitas perguntas estão associadas à tal questão, entre elas podemos citar: (i) Qual a natureza da substância, ou qual a origem do fenômeno, que está atualmente acelerando a expansão do universo? (ii) Por qual razão esta expansão acelerada iniciou recentemente (nos últimos 5-8 bilhões de anos), e não no passado distante ou no futuro remoto? (iii) Qual a variante inflacionária que operou no universo primitivo e qual sua conexão (se existe alguma) com o atual estágio acelerado do universo? Em nossa compreensão, as indagações acima fazem parte dos maiores problemas da cosmologia atual. A ampla abrangência de tais questões significa que avanços em qualquer uma delas terá implicações teóricas e observacionais em outras áreas envolvendo a interface formada pela Astronomia, Cosmologia e Física de Partículas. As três questões acima estão diretamente conectadas com os objetivos do presente trabalho. Acreditamos também que seu estudo pode lançar alguma luz e melhorar nossa compreensão sobre questões mais fundamentais da física. Neste contexto, analisamos diferentes modelos cosmológicos para a acelera- ção do universo à luz dos mais recentes dados observacionais de supernovas, radiação cósmica de fundo e oscilações acústicas de bárions. Propomos, aqui, alternativas ao Modelo Padrão da Cosmologia, ao mostrar que diversos fenômenos físicos podem estar associados à expansão do universo, gerando a aceleração observada sem a necessidade de se introduzir componentes desconhecidas no universo além da matéria escura. Além de desenvolver uma revisão crítica do Modelo Padrão, discutimos nesta tese especialmente três modelos para a expansão acelerada do universo. O primeiro deles considera a aceleração cósmica como sendo efeito da criação quântica de partículas de matéria escura, ou radiação, às custas do campo gravitacional variando continuamente com a expansão do universo. O segundo modelo considera o processo de viscosidade volumar no fluido cosmológico como sendo responsável pela aceleração. Esta viscosidade volumar se deve à perda de equilíbrio termodinâmico durante a expansão do fluido. O terceiro modelo, o modelo de decaimento do vácuo, considera como responsá- vel pela aceleração uma energia do vácuo que decai nas outras componentes cósmicas continuamente ao longo do tempo. Analisamos as relações existentes entre estes três modelos, além do Modelo Padrão, e as condições sob as quais os mesmos fornecem uma dinâmica equivalente para o universo. Também obtemos interessantes vínculos para os parâmetros destes modelos ao fazermos, além de uma análise observacional, uma análise teórica baseada na dinâmica e na termodinâmica associada a cada cenário. Sugerimos que estes cenários são capazes de aliviar diversos problemas conceituais do Modelo Padrão da Cosmologia. Numa segunda etapa, mostramos que os processos físicos descritos acima podem ser responsáveis tanto pela aceleração cósmica atual, quanto pela aceleração primordial que se supõe ter ocorrido no universo antigo. Tal abordagem fornece uma descrição unificada para a evolução cosmológica. Acreditamos ser de fundamental importância que o processo que dirigiu a aceleração primordial possa ser relacionado com o mesmo responsável pela atual fase de expansão acelerada do universo. Além disto, é possível que as dificuldades que atingem a interface que une a Relatividade Geral, a Cosmologia e a Teoria Quântica de Campos possam ser amenizadas através de uma melhor compreensão do processo de criação gravitacional de partículas, do decaimento do vácuo e suas conexões com o contexto da inflação primordial. Para comparar e vincular os modelos propostos, analisamos também o processo de formação das estruturas cosmológicas nestes modelos. Introduzimos a teoria de perturbações cosmológicas, primeiramente, através de uma análise do Modelo Padrão. A partir daí, apresentamos uma abordagem mais geral para o tratamento das perturbações chamada teoria de campo efetiva para a inflação. Neste contexto, analisamos quais previsões são obtidas ao se quebrar algumas suposições usualmente assumidas nestes modelos. Por fim, através de uma análise do espectro de potências primordial do modelo de criação gravitacional de partículas e do modelo de viscosidade, mostramos, pela primeira vez, que os mesmos podem ser capazes de gerar um cenário inflacionário para o universo primitivo em concordância com as observações atuais. / We are currently in a privileged moment for cosmology. In the last decade, the great progress of astronomical observations made possible that several cosmological models could be tested with great accuracy. With several observational data being released we obtained valuable information concerning the primordial acceleration of the universe and the recent accelerated expansion. Essentially, these observational efforts aim to clarify some of the most fundamental questions of modern cosmology, which concerns the understanding of the mechanism responsible for the acceleration of the universe. Many questions are related to this issue, among them we can mention: (i) What is the nature of the substance, or what is the origin of the phenomenom, responsible for the acceleration of the expansion? (ii) For which reason the accelerated expansion started recently (within the last 5-8 billion years), and not in the distant past or distant future? (iii) What is the inflationary variant that operated in the early universe, and what is its connection (if there is any) with the current accelerated stage of the universe? In our understanding the above questions are part of the biggest problems in modern cosmology. The interconnection between these issues means that advances in any of them will have theoretical and observational implications in other areas involving the interface formed by Astronomy, Cosmology and Particle Physics. The three questions above are directly connected to the objectives of this work. We also belive that their study can shed some light in our understanding of the remaining issues. In this context, we analyze different cosmological models for the acceleration of the universe in the light of the latest data released from supernovae, cosmic microwave background and baryon acoustic oscillations, comparing the results with the ones concerning the Standard Model of Cosmology. We propose alternatives to the Standard Model of Cosmology, by showing that several physical phenomena can be associated to the expansion of the universe, producing the observed acceleration without the need to introduce unknown components in the universe besides the dark matter. In addition to developing a critical revision of the Standard Model, we discuss in this thesis especially three models for the accelerated expansion of the universe. The first one considers the cosmic acceleration as an effect of the creation of dark matter particles, or radiation, at the expense of the gravitational field varying continuously with the expansion of the universe. The second model considers the process of bulk viscosity in the cosmological fluid as being responsible for the acceleration of the universe. This bulk viscosity is due to the loss of local thermodynamic equilibrium during the expansion of the fluid. The third model, the vacuum decaying model, considers as responsible for the acceleration, a vacuum energy which decays continuously into other cosmological components. We analyze the relations between these three models, and also the Standard Model, and the conditions under which they provide an equivalent dynamic to the universe. We also obtain interesting constraints for the parameters of these models by making, besides an observacional analysis, a theoretical analysis based on the dynamics and thermodynamics associated to each scenario. We will show that these alternative scenarios are able to alleviate several theoretical problems of the Standard Cosmological Model. In a second part, we show that the physical phenomena described above may be responsible for the recent cosmic acceleration, as well as for the primordial acceleration that is supposed to have occurred in the early universe. Such approach provides an unified description for the cosmological history. We belive it is of great importance that the process responsible for inflation can be identified with the one responsible for the current phase of accelerated expansion of the universe. Moreover, it is quite possible that the difficulties concerning the interface connecting General Relativity, Cosmology and Quantum Field Theory can be reduced through a better understanding of the gravitational particle creation process, the decay of the vacuum and its connections with the primordial inflationary context. In order to constrain and compare the models proposed here, we also analyse the process of cosmological structure formation in these models. We firstly introduce the perturbation theory through an analysis of the Standard Model. Then we introduce a more general approach to the treatment of cosmological perturbations which is called effective field theory of inflation. In this context, we analyse which predictions are obtained when we break some of the assumptions usually imposed in these models. Finally, through an analysis of the primordial power spectrum of the gravitational particle creation model and the viscosity model, we show, for the first time, that these models are able to describe an inflationary scenario for the early universe totally in agreement with current observations.

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.

I investigate the chemical evolution of the Universe in a series of cosmological hydrodynamic simulations with the purpose of finding a self-consistent evolutionary scenario of galaxy formation able to reproduce key observables focusing on the enrichment of the intergalactic medium (IGM). The most successful models I run and analyze use the scalings of momentum-driven feedback whereby UV photons generated during the Main Sequence stage accelerate dust-driven winds while providing a significantly larger energy budget than from supernovae alone. The success of this outflow model relies on its ability to drive highly mass-loaded winds from small galactic haloes. These feedback relations, supported by observations of local starburst, are inserted into simulations at all epochs, reproducing observables including the C IV column density and linewidth distributions at z=6->1.5 and the O VI forest at z=0-0.5. Outflows at z>=5 propagate early nucleosynthetic products traced by C IV and lower ionization species into an otherwise metal-free IGM. Continual outflows at the peak ages of star formation (z=5->1.5) produce a non-evolving cosmic mass density of C IV despite continual enrichment increasing IGM metallicity by a factor of ten. The z=0-0.5 O VI forest is composed of weaker absorbers tracing photo-ionized diffuse IGM metals, sometimes injected by primordial galaxies, and stronger absorbers tracing recently injected metals, often unable to escape their parent haloes and sometimes collisionally ionized. Tracking the individual histories of metals in outflows shows the average outflow travels ~100 physical kpc and returns to galaxies on an average timescale of 1-2 Gyr; this result implies metals in superwinds do not remain in the IGM for a Hubble time and are more likely to rejoin galaxies. Metal absorbers aligned with Lyman-alpha are examined in detail, finding that the two often trace different phases of gas with the former tracing an inhomogeneous distribution of metals exhibiting turbulence imparted during the outflow phase dissipating on a Hubble timescale. I find this is the first model to self-consistently reproduce the wide range of IGM observables spanning the history of heavy metal production while being consistent with key galaxy observables. The link between star formation and galactic superwinds requires that a successful model of galaxy formation reproduces both the evolution of galaxies and the IGM.