The standard paradigm of active galactic nuclei (AGN) postulates that their luminosity, L ~ 1039−48erg s−1, derives from the accretion of gas onto a supermassive black hole, mass M ~ 106−9M☉, at the centre of a host galaxy. Echo or reverberation mapping affords a method of relating flux variations at different wavelengths to determine the nature of the flux emitting regions, with μ-arcsecond resolution. The results of an intensive two-month campaign of ground based spectrophotometric monitoring of the Seyfert 1 galaxy NGC 7469, with a temporal resolution of ≤1 day, are presented. Application of echo mapping techniques reveal the virial mass of the central source to be MNGC 7469 ~106−7 M☉, and a compact broad Balmer line emitting region ~ 5 light days from the central source. Together, this evidence suggests the existence of a supermassive black hole in NGC 7469. Further, evidence for significant wavelength- dependent continuum time delays is presented, with optical continuum variations lagging those at UV wavelengths by about 1-2 days. The wavelength-dependent time delays, (λ), are consistent with the predicted T ∝ λ 4/ 3 relationship for an irradiated blackbody accretion disc with temperature structure T(R) ∝ R−3/4 and hence may represent the indirect detection of an accretion disc structure in NGC 7469. It is shown that wavelength-dependent time delays test the standard black-hole accretion disc paradigm of AGN, by measuring T(R) of the gaseous material surrounding the purported black hole. Moreover, a new direct method is presented that combines observed time delays and the spectral energy distribution of an AGN to derive a redshift-independent luminosity distance; assuming the observed time delays are indeed due to a classical accretion disc structure. The luminosity distance permits an estimate of the Hubble constant, H0-the expansion rate of the Universe. The first application of the method yields H0(cos i/0.7)1/2 = 38 ± 7km s−1 Mp −1. A more accurate determination of H0 requires either an independent accurate determination of the disc inclination i or statistical average of a moderate sample of active galaxies. This method permits determination of redshift-independent luminosity distances to AGNs, thereby, giving a new route to H0, and by extension to fainter objects at z ~ 1, q0.

Master of Science / Department of Physics / Bharat Ratra / Over three-quarters of observed galaxies are spiral galaxies, and of those spirals roughly two-thirds are barred. The Milky Way, a barred spiral galaxy, is naturally a great foundation to studying the structure of other barred spiral galaxies. Two important fundamental constants are used to describe the Milky Way, R₀ (the radial distance from the Sun to the Galactic center) and θ₀ (the Galactic rotational velocity at R₀). These two constants are also crucial for developing the rotation curve of the Galaxy, which helps to understand the mass distribution of the Galaxy and may be able to lend insight to the dark matter mass contribution. This work presents new, independently calculated values for R₀ and θ₀. The error distributions of a compilation of 28 (since 2011) independent measurements of R₀ are wider than a standard Gaussian and best fit by an n=4 Student's t probability density function. Given this non-Gaussianity, the results of our median statistics analysis, summarized as R₀ = 8.0 ± 0.3 kpc (2σ error), probably provides the most reliable estimate of R₀. The unsymmetrized value for R₀ is R₀ = 7.96+0.24-0.30 kpc (2σ error). A complete collection of 18 recent (since 2000) measurements of θ0 indicates a median statistics estimate of θ₀ = 220 ± 10 km/s ⁻¹ (2σ error) as the most reliable summary for most practical purposes, at R0 = 8.0 ± 0.3 kpc (2σ error). The resulting error distribution of this data set is only mildly non-Gaussian, much more so than that of R₀. These measurements use tracers that are believed to more accurately reflect the systematic rotation of the Milky Way. Unlike other recent compilations of R₀ and θ₀, our collections includes only independent measurements. This work concludes with a new set of Galactic constants (with 1σ error bars) of θ₀ = 222 ± 6 km s⁻¹, R₀ = 7.96 ± 0.17 kpc, and ω₀ = θ₀/ R₀ = 27.9 ± 1.0 km s⁻¹ kpc⁻¹ as probably the most reliable to date.

Conselho Nacional de Desenvolvimento Científico e Tecnológico / Formação de estruturas em larga escala é um problema em aberto em Cosmologia. Há um consenso de que a variedade de estruturas observadas tais como galáxias e aglomerados de galáxias tiveram origem a partir de pequenas flutuações do fluido cósmico possivelmente geradas durante a época inflacionária na era dominada pela matéria. Os estágios iniciais da evolução destas flutuações são descritas pela teoria de Jeans resultante da aproximação linear das equações hidrodinâmicas. Basicamente, a instabilidade devido à ação do campo gravitacional induz à existência de dois tipos de modos perturbativos: os modos instáveis que crescem, e os estáveis que oscilam como ondas sonoras. A distinção entre estes modos depende se o comprimento de onda de um determinado modo perturbativo é maior ou menor que um comprimento de onda típico conhecido como o comprimento de Jeans. Eventualmente, o crescimento dos modos instáveis quebra a aproximação e efeitos não-lineares tornam-se cruciais para a formação de estruturas. Neste sentido, nosso objetivo é estudar o problema não-linear de formação de estruturas em um Universo em expansão dominado pela matéria considerando uma extensão consistente da teoria linear de Jeans. Uma aproximação por sistema dinâmico é fornecida pelo método de Galerkin usado para integrar as equações dinâmicas do fluido auto-graviante. Conseqüentemente é exibido o comportamento dos modos perturbativos instáveis e estáveis do fluido cósmico além do regime linear anterior à formação de estruturas. Nós também consideramos consistentemente a influência da viscosidade ao invés de introduzi-la de um modo artificial como no modelo de Adesão. / The formation of large scale structure is an outstanding problem in Cosmology. It is a consensus that the observed variety of structures such as galaxies and clusters of galaxies have originated from small fluctuations of the cosmic fluid possibly generated during the inflationary epoch-in the matter dominated era. The early stages of evolution of these fluctuations are described by the Jeans theory resulting from the linear approximation of the hydrodynamical equations. Basically, the instabilities due the action of the gravitational field induce the existence of two types of perturbativo modes: the unstable modes that grow, and the stable one that oscillate as sound waves. The distinction between these modes depend son whether the wave length of a given perturbativo mode is greater or smaller than atypical wave-length known as the Jeans length. Eventually, the growth of the unstable modes breaks the linear approximation and nonlinear effects turn out to be crucial for the formation of structures. In this vein, our objective here is to study the problem of nonlinear structure formation in a matter dominated expanding universe considering a consistent extension of the linear Jeans theory. A dynamical system approach is provided by the Galerkin method used to integrate the self-gravitating fluid dynamical equations. Therefore, the behavior of the unstable and stable perturbative modes of the cosmic fluid are exhibited beyond the linear regime prior the formation of structures. We have also considered the influence of viscosity consistently rather than introducing it in an artificial way as in the Adhesion Model.

Made available in DSpace on 2015-12-10T14:24:06Z (GMT). No. of bitstreams: 0 Previous issue date: 2015-06-09. Added 1 bitstream(s) on 2015-12-10T14:30:15Z : No. of bitstreams: 1 000852869.pdf: 540584 bytes, checksum: 876f75004ad5a8e7b7dbf74986332aea (MD5) / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES) / A assimetria temporal observada na física macroscópica se deve à configuração de entropia extremamente baixa do universo primordial. Apesar de a matéria estar muito quente e com uma temperatura uniforme naquele estágio, os graus de liberdade gravitacionais estavam em grande medida suprimidos, fato este que contribui para o baixo valor da entropia e está codificado no alto grau de simetria espacial (caráter aproximadamente Friedman-Lemaître-Robertson-Walker) da superfície de último espalhamento. Analisamos diferentes tentativas de explicar a origem de tal configuração especial. O paradigma inflacionário é testado com respeito a esse problema, e é concluído que a baixa entropia inicial não pode ser explicada dentro dele. Conclusões similares são obtidas com respeito a formulações estatísticas (i.e. antrópicas). Por outro lado, o paradigma conhecido como cosmologia cíclica conforme (CCC) se apresenta como uma nova alternativa que ultrapassa muitas das dificuldades enfrentadas pelos seus rivais, apesar de levantar suas próprias questões em aberto. Introduzimos o modelo juntamente com a estrutura matemática das geometrias de Cartan como um meio possível de atingir um melhor entendimento das condições de contorno cosmológicas. Um elemento que é crucial nessa análise é a modelagem de uma estrutura geométrica de Cartan sobre o espaço de de Sitter SOe(4,1)/SOe(3,1) com um parâmetro de comprimento variável. A introdução de um parâmetro de comprimento na cinemática é favorecida pela observação de uma constante cosmológica positiva e também desejável por motivos oriundos da gravitação quântica, devido à escala natural determinada pelo comprimento de Planck / The observed T-asymmetry of macroscopic physics is traced back to the extremely low entropy configuration of the early universe. Although matter was very hot and with a uniform temperature at that stage, the gravitational degrees of freedom were largely suppressed, which fact contributes to the lowness of the entropy and is encoded in the high level of spatial symmetry (nearly Friedman-Lemître-Robertson-Walker character) of the last scattering surface. I analyze different attempts to explain the origin of such special configuration. The inflation paradigm is probed with respect to this problem, and it is concluded that the initial low entropy cannot be accounted for within it. Similar conclusions are reached with respect to statistical (i.e. anthropic) reasonings. On the other hand, the paradigm known as conformal cyclic cosmology (CCC) presents itself as a new alternative which surpasses many of the difficulties faced by its rivals, although raising its own open questions. I introduce the model together with the mathematical structure of Cartan geometries as a possible means of achieving a better understanding of cosmological boundary conditions. One element which is crucial in this analysis is the modeling of the Cartan geometric structure over a de Sitter space SOe(4,1)/SOe(3,1) with varying length parameter. The introduction of a length parameter in the kinematics is favored by the observation of a positive cosmological constant and also desirable for quantum gravity reasons, due to the natural scale set by Planck's constant

Made available in DSpace on 2014-06-11T19:31:24Z (GMT). No. of bitstreams: 0 Previous issue date: 2010-12-20Bitstream added on 2014-06-13T20:41:38Z : No. of bitstreams: 1 sanoja_a_dr_ift.pdf: 582908 bytes, checksum: 608a543719b2da86f0b937d5c00bfbba (MD5) / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES) / Fazemos uma revisão do modelo cosmológico padrão, apresentando suas bases observacionais e mostrando os aspectos conceituais mais relevantes. Depois realizamos uma revisão da teoria de in ação, indicando as motivações conceituais que levaram à formulação da teoria, o mecanismo que faz possível a in ação cósmica e como esse processo resolve os problemas clássicos da cosmologia padrão. Após mostrar que a in ação é um mecanismo bem-sucedido para explicar a origem das perturbações de densidade primordiais, concentramo-nos em descrever a evolução das perturbações de densidade cosmológica, tanto na sua fase linear como não-linear. Além disso, mostramos como o campo de perturbações de densidade linear permite predizer estatisticamente a abundância e a distribuição das estruturas cósmicas. Posteriormente, consideramos a expansão acelerada do universo e discutimos os candidatos que têm sido propostos para tentar explicar a origem dessa aceleração, especialmente o candidato da energia escura, no qual nos detemos para revisar os modelos básicos propostos com respeito à sua natureza. Adicionalmente, mostramos como sua presença afeta a evolução das perturbações de densidade. Finalmente, baseandonos no modelo de Lemaître-Tolman-Bondi, fazemos uma generalização do modelo do colapso esférico para estudar a evolução não-linear de perturbações de densidade inhomogêneas, tanto em um universo Einstein-de Sitter como em um universo CDM / We present a review of the standard cosmological model, showing both its observational basis as well as the most revelant conceptual aspects. Subsequently, we give an overview of the in ation theory , pointing out the conceptual motivations that led to its formulation, the mechanism that allow the cosmic in ation and how that process resolves the classical problems of the standard cosmology. After showing that the in ation theory provides a successful mechanism to explain the origin of the primordial density perturbations, we focus on describing the evolution of the cosmological density perturbations, both in linear and nonlinear phase. On the other hand, we show how the linear density perturbation eld allows to predict statistically the abundance and distribution of the cosmic structures. Next, we consider the accelerated expansion of the universe and mention the candidates that have seen proposed to try to explain the origin of the acceleration; especially the dark energy candidate, in which we pause to examine the basic models proposed about its nature. Further, we expose how its presence a ects the evolution of the density perturbations. Finally, based on the Lemaître-Tolman-Bondi, we make a generalization of the spherical collapse model to study the evolution of inhomogeneous nonlinear density perturbations, both in an Einstein-de Sitter as CDM universe

Made available in DSpace on 2014-06-11T19:32:09Z (GMT). No. of bitstreams: 0 Previous issue date: 2011-09-02Bitstream added on 2014-06-13T21:03:29Z : No. of bitstreams: 1 sobreira_f_dr_ift.pdf: 3580340 bytes, checksum: 5b2c8fe81dd5d4ebcb30572e1f260ebc (MD5) / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES) / Nesta tese estudamos previsões sobre os erros nos parâmetros cosmológicos usando a forma integral da função de correlação angular de dois pontos em diferentes cenários para o projeto Dark Energy Survey. O modelo adotado tem 26 parâmetros e inclui efeitos de distorção no redshift, erros gaussianos de redshift fotométrico, viés da distribuição de galáxias e matéria escura e não-linearidade no espectro de potência. A matriz de Fisher foi construída usando a matriz de covariância considerando a correlação entre diferentes faixas de redshift. Mostramos que, sobre alguma hipóteses, o Dark Energy Survey será capaz de vincular o parâmetro da equação de estado de energia escura w e o parâmetro da densidade de matéria escura fria 'Ω IND cdm' com incerteza de 21% e 13% respectivamente. Quando combinamos informações de outras observações a precisão na determinação destes parâmetros aumenta para 11% e 4% respectivamente / In this thesis, we study forecasts of cosmological parameters from the upcoming Dark Energy Survey project obtained using the full shape 2-point angular correlation function in different scenarios. The angular correlation function model adopted has 26 parameters and includes the effects of linear redshift space distortion, photometric redshift gaussian errors, galaxy bias and non-linearities in the power spectrum. The Fisher information matrix is constructed with the full covariance matrix, which takes into account the correlation between nearby redshift shells arising from the photometric redshift error. We show that under some resonable assumptions the Dark Energy Survey should be able to constrain the dark energy equation of estate parameter w and the cold dark matter density 'Ω IND cdm' with a precision of the order of 21% and 13% respectively from the full shape of the angular correlation function alone. When combined with priors from other observations the precision in the determination of these parameters increase to 11% and 4% respectively

Conselho Nacional de Desenvolvimento Científico e Tecnológico / Formação de estruturas em larga escala é um problema em aberto em Cosmologia. Há um consenso de que a variedade de estruturas observadas tais como galáxias e aglomerados de galáxias tiveram origem a partir de pequenas flutuações do fluido cósmico possivelmente geradas durante a época inflacionária na era dominada pela matéria. Os estágios iniciais da evolução destas flutuações são descritas pela teoria de Jeans resultante da aproximação linear das equações hidrodinâmicas. Basicamente, a instabilidade devido à ação do campo gravitacional induz à existência de dois tipos de modos perturbativos: os modos instáveis que crescem, e os estáveis que oscilam como ondas sonoras. A distinção entre estes modos depende se o comprimento de onda de um determinado modo perturbativo é maior ou menor que um comprimento de onda típico conhecido como o comprimento de Jeans. Eventualmente, o crescimento dos modos instáveis quebra a aproximação e efeitos não-lineares tornam-se cruciais para a formação de estruturas. Neste sentido, nosso objetivo é estudar o problema não-linear de formação de estruturas em um Universo em expansão dominado pela matéria considerando uma extensão consistente da teoria linear de Jeans. Uma aproximação por sistema dinâmico é fornecida pelo método de Galerkin usado para integrar as equações dinâmicas do fluido auto-graviante. Conseqüentemente é exibido o comportamento dos modos perturbativos instáveis e estáveis do fluido cósmico além do regime linear anterior à formação de estruturas. Nós também consideramos consistentemente a influência da viscosidade ao invés de introduzi-la de um modo artificial como no modelo de Adesão. / The formation of large scale structure is an outstanding problem in Cosmology. It is a consensus that the observed variety of structures such as galaxies and clusters of galaxies have originated from small fluctuations of the cosmic fluid possibly generated during the inflationary epoch-in the matter dominated era. The early stages of evolution of these fluctuations are described by the Jeans theory resulting from the linear approximation of the hydrodynamical equations. Basically, the instabilities due the action of the gravitational field induce the existence of two types of perturbativo modes: the unstable modes that grow, and the stable one that oscillate as sound waves. The distinction between these modes depend son whether the wave length of a given perturbativo mode is greater or smaller than atypical wave-length known as the Jeans length. Eventually, the growth of the unstable modes breaks the linear approximation and nonlinear effects turn out to be crucial for the formation of structures. In this vein, our objective here is to study the problem of nonlinear structure formation in a matter dominated expanding universe considering a consistent extension of the linear Jeans theory. A dynamical system approach is provided by the Galerkin method used to integrate the self-gravitating fluid dynamical equations. Therefore, the behavior of the unstable and stable perturbative modes of the cosmic fluid are exhibited beyond the linear regime prior the formation of structures. We have also considered the influence of viscosity consistently rather than introducing it in an artificial way as in the Adhesion Model.

Blue stragglers are enigmatic stars which appear to have undergone some form of rejuvenation, bringing them near the zero-age main sequence of the cluster in which they reside. The most likely explanation for the existence of these stars is that they have formed recently, through the merger of two stars, either through a direct stellar collision, or through binary mass-transfer and coalescence. This thesis presents models of the remnants of these processes, and a comparison of the predictions of these models with observed blue stragglers in several clusters. The predictions of smoothed particle hydrodynamic simulations of colliding stars have been used to create models appropriate for input into a stellar evolution code. Since these models develop only thin, short-lived, convective envelopes, angular momentum loss via a magnetically driven stellar wind is unlikely to be a viable mechanism for slowing the rapidly rotating blue stragglers predicted by the collisional scenario. Angular momentum transfer to either a circumstellar disk (possibly collisional ejecta) or a nearby companion remain plausible mechanisms for explaining the low rotation velocities observed for most blue stragglers. In addition to these models of collisional mergers, simplistic models of the remnants of binary coalescence and mass-transfer were also developed. The predictions of both sets of models were compared with the observed blue straggler populations of six globular clusters (NGC 104, NGC 2419, NGC 5024, NGC 6809, NGC 7099). While most of the clusters' blue stragglers appear to be well matched by the predictions of the collisional mergers, the blue stragglers in the cluster with the highest central density, NGC 7099, appear to be a hybrid population of both collisional and binary mergers. The blue stragglers of NGC 2419—the least dense of the clusters studied here—are well matched solely by the predictions of the collisional mergers of equal mass stars. However, due to the low density of this cluster, it is likely that some fraction of these blue stragglers are being formed via binary mergers and that the mergers and that the simple models of binary mergers used here are inadequate. / Graduate

The observed accelerated expansion of the universe is one of the big issues of modern cosmology. One possible way of understanding it is by modifying General Relativity so that gravity is weaker at large scales. Higher-dimensional models that offer infrared modifications of gravity provide just that. Braneworld models are a subclass of these, where standard matter is confined to a p dimensional brane living in a p+d dimensional “bulk” space. Gravitons, however, can access the extra d dimensions. The Dvali-Gabadadze-Porrati(DGP) model realizes this by having a 4D brane embedded in 5D space-time. By including an induced gravity term in the action, standard 4D gravity is recovered at small scales, whereas at large scales gravity is 5D. This model is particularly interesting because of its phenomenology, namely the existence of two cosmological branches, one of which, called the self-accelerating branch, exhibits late time cosmic acceleration even when no matter is present in the brane. However, such cosmologies, at the linear level, have been found to be plagued by ghost instabilities that cause a catastrophic instability of space-time thus automatically excluding the model as a viable explanation of reality. In this thesis, after a brief introduction to the covered topics, we start by going beyond linearity to see if non-linear interactions might change previous results on the presence of the ghost. We did this for a cosmological background and, in the process, derived the equations that form the basis of structure formation tests in the DGP model. Our analysis however, proves the validity of the linearized solutions and, thus, the presence of the ghost. We then used a numeric algorithm to solve the full 5D set of dynamical equations for the scalar perturbations in the DGP model. Our numeric solutions are the basis for comparison of the ghost-free normal branch with cosmological observations. Whereas there seems to be no way of avoiding the ghost problem in the self-accelerating branch of the DGP model, a generalization of it that removes the symmetry across the brane had been shown to be ghost-free in a flat background while retaining some form of late-time acceleration (given the name of stealth acceleration) in certain limits. We study the spectrum of perturbations for a de Sitter background in the same setup. Our analysis showed that the only way to avoid a ghost is precisely to have Minkowski branes. Finally, yet another generalization of the DGP model, in this case a generalization of its 4D effective action called the Galileon model, is shown to possess the self-accelerating solutions. We present an extension of the Brans-Dicke theory by adding a third order Galileon term to the Brans-Dicke action that appears in the 4D effective theory of DGP gravity. An analysis of our model shows the presence of self-acceleration for a certain region of it’s parameter space, without any ghost or tachyonic instabilities.

The use of Baryon Acoustic Oscillations (BAO) as a standard ruler in the 2-point galaxy clustering signal has proven to be an excellent probe of the cosmological expansion. With the abundance of good quality galaxy data predicted for future large sky surveys, the potential to conduct precision cosmology using clustering analyses is immense. Many of the next generation sky surveys, including the Dark Energy Survey (DES), the Panoramic Survey Telescope and Rapid Response System (PanStarrs), and the Large Synoptic Survey Telescope (LSST), will utilise photometric redshift estimation techniques, which will make it possible to probe wider and deeper regions of the Universe than spectroscopic redshift surveys in an equivalent amount of time. The use of photometric techniques to estimate galaxy redshifts however, induces errors on inferred radial distances. Consequently, the amplitude of the power spectrum and correlation function is reduced in the radial direction by this smoothing. In this regime, precise measurements of the BAO signal will be difficult. Because of this, there is an urgent need to obtain a better understanding of exactly how photometric redshift uncertainties affect 3D clustering analyses, and to investigate alternative clustering analysis techniques that may be used in future experiments. In this thesis, I investigate the systematic effects arising in the projected correlation function due to redshift-space distortions, and introduce a new binning scheme to eradicate the problem. I also consider the level of systematic uncertainty induced in realistic measurements of the 3D correlation function from conflicting photometric redshift estimation techniques, and highlight a requirement for empirical test results to be incorporated into model predictions of the anisotropic correlation function for future surveys. Finally, I collate my results to make predictions about how BAO can be optimally used in future photometric redshift experiments like the DES.