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Dupuy, Hélène. "Precision cosmology with the large-scale structure of the universe." Thesis, Paris 6, 2015. http://www.theses.fr/2015PA066245/document.
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Cette thèse fournit des résultats innovants de plusieurs types. Leur point commun est la quête de précision dans la description des phénomènes physiques à l'œuvre dans l'univers. D'abord, un modèle-jouet simulant la propagation de la lumière dans un espace-temps non homogène est présenté. Dans cette étude, nous avons opté pour la traditionnelle représentation de type Swiss cheese. Souvent utilisée dans la littérature, elle permet de travailler avec des solutions exactes de la relativité générale, qui n'altèrent pas la dynamique globale de l'univers tout en le rendant fortement non homogène. Nous avons illustré la façon dont les hypothèses de base, telles que le principe cosmologique, peuvent affecter les conclusions scientifiques, telles que l'estimation des paramètres cosmologiques à partir des diagrammes de Hubble. Ce travail a donné lieu à deux publications en 2013, une dans Physical Review D et une autre dans Physical Review Letter. Le résultat majeur proposé dans cette thèse est une nouvelle façon de décrire les neutrinos en cosmologie. L'idée est de décomposer les neutrinos en plusieurs fluides à un flot de manière à se débarrasser de la dispersion en vitesse dans chacun d'eux. Cela s'inscrit dans le cadre de l'étude de la formation des grandes structures de l'univers à l'aide de la théorie des perturbations cosmologiques dans les régimes non linéaire et/ou relativiste. Ce travail a donné lieu à trois publications dans JCAP, une en 2014 et deux en 2015This thesis provides innovative results of different types. What they have in common is the quest for precision in the description of the physical phenomena at work in the universe. First, a toy model mimicking the propagation of light in an inhomogeneous spacetime has been presented. In this study, we chose a traditional Swiss-cheese representation. Often used in the litterature, such models offer the advantage of dealing with exact solutions of the Einstein equations, which do not affect the global dynamics of the universe while making it strongly inhomogeneous. We have exemplified how initial presumptions, such as the cosmological principle, can alter scientific conclusions, such as the estimation of cosmological parameters from Hubble diagrams. This work resulted in two publications in 2013, one in Physical Review D and another one in Physical Review Letter. The major result exposed in this thesis is the proposition of a new way of dealing with the neutrino component in cosmology. The idea is to decompose neutrinos into several single-flow fluids in order to get rid of velocity dispersion in each of them. The research field to which it belongs is the study of the formation of the large-scale structure of the universe thanks to cosmological perturbation theory in the relativistic and/or nonlinear regimes. This work resulted in three publications in JCAP, one in 2014 and two in 2015
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Mehta, Kushal Tushar. "Measuring the Universe with High-Precision Large-Scale Structure." Diss., The University of Arizona, 2014. http://hdl.handle.net/10150/325226.
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Baryon acoustic oscillations (BAOs) are used to obtain precision measurements of cosmological parameters from large-scale surveys. While robust against most systematics, there are certain theoretical uncertainties that can affect BAO and galaxy clustering measurements. In this thesis I use data from the Sloan Digital Sky Survey (SDSS) to measure cosmological parameters and use N-body and smoothed-particle hydrodynamic (SPH) simulations to measure the effect of theoretical uncertainties by using halo occupation distributions (HODs). I investigate the effect of galaxy bias on BAO measurements by creating mock galaxy catalogs from large N -body simulations at z = 1. I find that there is no additional shift in the acoustic scale (0.10% ± 0.10%) for the less biased HODs (b < 3) and a mild shift (0.79% ± 0.31%) for the highly biased HODs (b > 3). I present the methodology and implementation of the simple one-step reconstruction technique introduced by Eisenstein et al. (2007) to biased tracers in N-body simulation. Reconstruction reduces the errorbars on the acoustic scale measurement by a factor of 1.5 - 2, and removes any additional shift due to galaxy bias for all HODs (0.07% ± 0.15%). Padmanabhan et al. (2012) and Xu et al. (2012) use this reconstruction technique in the SDSS DR7 data to measure Dᵥ(z = 0.35)(rᶠⁱᵈs/rs) = 1356 ± 25 Mpc. Here I use this measurement in combination with measurements from the cosmic microwave background and the supernovae legacy survey to measure various cosmological parameters. I find the data consistent with the ΛCDM Universe with a flat geometry. In particular, I measure H₀ = 69.8 ± 1.2 km/s/Mpc, w = 0.97 ± 0.17, Ωk = -0.004 ± 0.005 in the ΛCDM, wCDM, and oCDM models respectively. Next, I measure the effect of large-scale (5 Mpc) halo environment density on the HOD by using an SPH simulation at z = 0, 0.35, 0.5, 0.75, 1.0. I do not find any significant dependence of the HOD on the halo environment density for different galaxy mass thresholds, red and blue galaxies, and at different redshifts. I use the MultiDark N-body simualtion to measure the possible effect of environment density on the galaxy correlation function ℰ(r). I find that environment density enhances ℰ(r) by ∽ 3% at scales of 1 – 20h⁻¹Mpc at z = 0 and up to ∽ 12% at 0.3h⁻¹Mpc and ∽ 8% at 1 - 4h⁻¹Mpc for z = 1.
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McGill, Colin Andrew. "The large-scale structure of the universe : some theoretical considerations." Thesis, University of Oxford, 1987. http://ora.ox.ac.uk/objects/uuid:967fd0f2-817e-48ae-b57c-c1fb0dd435fb.
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In this thesis, several theoretical concepts relating to the large-scale structure of the universe are presented. In particular, various aspects of the hierarchical scenario are investigated. The initial perturbation field and its early evolution are discussed in Chapter 3. Chapter 4 is concerned with two-point correlation functions for galaxies, clusters and super-clusters. In Chapter 5, some effects of using velocity as a distance measure are examined. In particular, it will be argued that caustics in redshift space are an almost inevitable feature of the hierarchical scenario. Chapter 6 concentrates on the possibity that quasar Ly-α absorption lines are redshift caustics.
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Ntelis, Pierros. "Probing Cosmology with the homogeneity scale of the universe through large scale structure surveys." Thesis, Sorbonne Paris Cité, 2017. http://www.theses.fr/2017USPCC200/document.
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Cette thèse présente ma contribution à la mesure de l’échelle d’homogénéité à l’aide de galaxies, avec l’interprétation cosmologique des résultats. En physique, tout modèle est constitué par un ensemble de principes. La plupart des modèles de cosmologie sont basés sur le principe cosmologique, qui indique que l’univers est statistiquement homogène et isotrope à grande échelle. Aujourd’hui, ce principe est considéré comme vrai car il est respecté par ces modèles cosmologiques qui décrivent avec précision les observations. Cependant, l’isotropie de l’univers est maintenant confirmée par de nombreuses expériences, mais ce n’est pas le cas pour l’homogénéité. Pour étudier l’homogénéité cosmique, nous proposons un postulat d’homogénéité cosmique. Depuis 1998, les mesures des distances cosmiques à l’aide de supernovae de type Ia, nous savons que l’univers est maintenant en phase d’expansion accélérée. Ce phénomène s’explique par l’ajout d’une composante énergétique inconnue, appelée énergie sombre. Puisque l’énergie noire est responsable de l’expansion de l’univers, nous pouvons étudier ce fluide mystérieux en mesurant le taux d’expansion de l’univers. L’échelle d’oscillation acoustique Baryon (BAO). En mesurant cette échelle à différents moments de la vie de notre univers, il est alors possible de mesurer le taux d'expansion de l’univers et donc de caractériser cette énergie sombre. Alternativement, nous pouvons utiliser l’échelle d’homogénéité pour étudier cette énergie sombre. L’étude l’échelle de l’homogénéité et l’échelle BAO réclament l’étude statistique du regroupement de la matière de l’univers à grandes échelles, supérieure à plusieurs dizaines de Megaparsecs. Les galaxies et les quasars sont formés dans les vastes surdensités de la matière et ils sont très lumineuses: ces sources tracent la distribution de la matière. En mesurant les spectres d’émission de ces sources en utilisant de larges études spectroscopiques, telles que BOSS et eBOSS, nous pouvons mesurer leurs positions. Il est possible de reconstruire la distribution de la matière en trois dimensions en volumes gigantesques. Nous pouvons ensuite extraire divers observables statistiques pour mesurer l’échelle BAO et l’échelle d’homogénéité de l’univers. En utilisant les catalogues de diffusion de données 12 de la version 12 de données, nous avons obtenu une précision sur l’échelle d’homogénéité réduite de 5 par rapport la mesure de WiggleZ. À grande échelle, l’univers est remarquablement bien décrit en ordre linéaire selon le modèle LCDM, le modèle standard de la cosmologie. En général, il n’est pas nécessaire de prendre en compte les effets non linéaires qui compliquent le modèle à petites échelles. D’autre part, à grande échelle, la mesure de nos observables devient très sensible aux effets systématiques. Ceci est particulièrement vrai pour l’analyse de l’homogénéité cosmique, qui nécessite une méthode d’observation. Afin d’étudier le principe d’homogénéité d’une manière indépendante du modèle, nous explorons une nouvelle façon d’inférer des distances en utilisant des horloges cosmiques et SuperNovae de type Ia. C'est la théorie la plus couramment utilisée dans le domaine des hypothèses astrophysiquesThis thesis exposes my contribution to the measurement of homogeneity scale using galaxies, with the cosmological interpretation of results. In physics, any model is characterized by a set of principles. Most models in cosmology are based on the Cosmological Principle, which states that the universe is statistically homogeneous and isotropic on a large scales. Today, this principle is considered to be true since it is respected by those cosmological models that accurately describe the observations. However, while the isotropy of the universe is now confirmed by many experiments, it is not the case for the homogeneity. To study cosmic homogeneity, we propose to not only test a model but to test directly one of the postulates of modern cosmology. Since 1998 the measurements of cosmic distances using type Ia supernovae, we know that the universe is now in a phase of accelerated expansion. This phenomenon can be explained by the addition of an unknown energy component,which is called dark energy. Since dark energy is responsible for the expansion of the universe, we can study this mysterious fluid by measuring the rate of expansion of the universe. Nature does things well: the universe has imprinted in its matter distribution a standard ruler, the Baryon Acoustic Oscillation (BAO) scale. By measuring this scale at different times in the life of our universe, it is then possible to measure the rate of expansion of the universe and thus characterize this dark energy. Alternatively, we can use the homogeneity scale to study this dark energy. Studying the homogeneity and the BAO scale requires the statistical study of the matter distribution of the universe at large scales, superior to tens of Megaparsecs. Galaxies and quasars are formed in the vast overdensities of matter and they are very luminous: these sources trace the distribution of matter. By measuring the emission spectra of these sources using large spectroscopic surveys, such as BOSS and eBOSS, we can measure their positions. It is thus possible to reconstruct the distribution of matter in 3 dimensions in gigantic volumes. We can then extract various statistical observables to measure the BAO scale and the scale of homogeneity of the universe. Using Data Release 12 CMASS galaxy catalogs, we obtained precision on the homogeneity scale reduced by 5 times compared to WiggleZ measurement. At large scales, the universe is remarkably well described in linear order by the ΛCDM-model, the standard model of cosmology. In general, it is not necessary to take into account the nonlinear effects which complicate the model at small scales. On the other hand, at large scales, the measurement of our observables becomes very sensitive to the systematic effects. This is particularly true for the analysis of cosmic homogeneity, which requires an observational method so as not to bias the measurement In order to study the homogeneity principle in a model independent way, we explore a new way to infer distances using cosmic clocks and type Ia SuperNovae. This establishes the Cosmological Principle using only a small number of a priori assumption, i.e. the theory of General Relativity and astrophysical assumptions that are independent from Friedmann Universes and in extend the homogeneity assumption
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Hatton, Stephen John. "Probing the large-scale structure of the Universe with future galaxy redshift surveys." Thesis, Durham University, 1999. http://etheses.dur.ac.uk/4494/.
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Several projects are currently underway to obtain large galaxy redshift surveys over the course of the next decade. The aim of this thesis is to study how well the resultant three-dimensional maps of the galaxy distribution will be able to constrain the various parameters of the standard Big Bang cosmology. The work is driven by the need to deal with data of far better quality than has previously been available. Systematic biases in the treatment of existing datasets have been dwarfed by random errors due to the small size of the sample, but this will not be the case with the wealth of data that will shortly become available. We employ a set of high-resolution /V-body simulations spanning a range of cosmologies and galaxy biasing schemes. We use the power spectrum of the galaxy density field, measured using the fast Fourier transform process, to develop models and statistics for extracting cosmological information. In particular, we examine the distortion of the power spectrum by galaxy peculiar velocities when measurements are made in redshift space. Mock galaxy catalogues are drawn from these simulations, mimicking the geometries and selection functions of the large surveys we wish to model. Applying the same models to the mock catalogues is not a trivial task, as geometrical effects distort the power spectrum, and measurement errors are determined by the survey volume. We develop methods for assessing these effects and present an in-depth analysis of the likely confidence intervals we will obtain from the surveys on the parameters that determine the power spectrum. Real galaxy catalogues are prone to additional biases that must be assessed and removed. One of these is the effect of extinction by dust in the Milky Way, which imprints its own angular clustering signal on the measured power spectrum. We investigate the strength of this effect for the SDSS survey.
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Melia, Fulvio. "The linear growth of structure in the Rh = ct universe." OXFORD UNIV PRESS, 2017. http://hdl.handle.net/10150/622916.
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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.
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Manti, Serena. "Cosmic large scale structure: insights from radio astronomical experiments." Doctoral thesis, Scuola Normale Superiore, 2016. http://hdl.handle.net/11384/85877.
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From the introduction: "In this Thesis work we focus on the fundamental role that the Square Kilometre Array (SKA) will play in the search for Radio Recombination Lines (RRLs) from quasars and in radio-continuum observations of large scale structures, as, e.g. galaxy clusters. Moreover, we investigate the relationship between quasars and their host galaxies through studies of the cosmic LSS".
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Croft, Rupert Alfred Charles. "Galaxy clusters and the formation of large-scale structures in the universe." Thesis, University of Oxford, 1995. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.308751.
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Hoyle, Fiona. "The structure and scale of the universe." Thesis, Durham University, 2000. http://etheses.dur.ac.uk/4250/.
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We quantify the structure and scale of the Universe using redshift surveys of galaxies and QSOs and observations of Galactic open star clusters. We obtain the galaxy power spectrum from the Durham/UKST Galaxy Redshift Survey. By comparing the shape of the observed power spectrum to the APM real space power spectrum, we quantify the size of the redshift space distortions and find β = Ω(^0.6)/b=0.60±0.35. We also apply counts-in-cells analysis to the Durham/UKST and Stromlo-APM Surveys and measure the skewness directly out to 20h(^-1)Mpc. We find that the skewness measured from CDM models can only be reconciled with that of galaxies if bias is non-linear. We make predictions for the clustering in the 2dF QSO Survey by constructing mock catalogues from the Hubble Volume N-body simulation, with geometry, selection function and clustering matching those expected in the completed Survey. We predict that the correlation function will be reliably measured out to ~ 1, 000h(^-1)Mpc and the power spectrum out to 500h(^-1)Mpc. We measure the power spectrum from the 2dF QSOs observed by January 2000 and find it has a shape of F ~ 0.1. We also find little evolution in the clustering amplitude as a function of redshift. We obtain constraints on the cosmo- logical parameters Ωn and β by combining results from modeling geometric distortions introduced into the clustering pattern due to inconsistent cosmological assumptions and results from the QSO-mass bias. Finally, we consider the scale of the Universe. We check the calibration of the Cepheid Period-Luminosity relation using U,B,V and K'band imaging of Galactic Open Clusters containing Cepheids and measure the distance modulus to the LMC to be 18.51 ±0.10. However, we find anomalous colour-colour diagrams for two clusters and suggest that the effects of metallicity may be greater than previously considered.
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Collis, Olivari Lucas. "Intensity mapping : a new approach to probe the large-scale structure of the Universe." Thesis, University of Manchester, 2018. https://www.research.manchester.ac.uk/portal/en/theses/intensity-mapping-a-new-approach-to-probe-the-largescale-structure-of-the-universe(cd5b7586-7210-441e-838f-545d397893e5).html.
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Intensity mapping (IM) is a new observational technique to survey the large-scale structure of matter using emission lines, such as the 21 cm emission line of atomic hydrogen (HI) and the rotational lines of the carbon monoxide molecule (CO). Sensitive radio surveys have the potential to detect the HI power spectrum at low redshifts (z <1) in order to constrain the properties of dark energy and massive neutrinos. Observations of the HI signal will be contaminated by instrumental noise and, more significantly, by astrophysical foregrounds, such as the Galactic synchrotron emission, which is at least four orders of magnitude brighter than the HI signal. In this thesis, we study the ability of the Generalized Needlet Internal Linear Combination (GNILC) method to subtract radio foregrounds and to recover the cosmological HI signal for HI IM experiments. The GNILC method is a new technique that uses both frequency and spatial information to separate the components of the observed data. For simulated radio observations including HI emission, Galactic synchrotron, Galactic free-free, extragalactic point sources and thermal noise, we find that it can reconstruct the HI plus noise power spectrum with 7.0% accuracy for 0.13 <z <0.48 (960 - 1260 MHz) and l <400. In this work, GNILC is also applied to a particular CO IM experiment: the CO Mapping Array Pathfinder (COMAP). In this case, the simulated radio observations include CO emission, Galactic synchrotron, Galactic free-free, Galactic anomalous microwave emission, extragalactic point sources and thermal noise. We find that GNILC can reconstruct the CO plus noise power spectra with 7.3% accuracy for COMAP phase 1 (l <1800) and 6.3% for phase 2 (l <3000). In both cases, we have 2.4 <z <3.4 (26 - 34 GHz). In this work, we also forecast the uncertainties on cosmological parameters for the upcoming HI IM experiments BINGO (BAO from Integrated Neutral Gas Observations) and SKA (Square Kilometre Array) phase-1 dish array operating in auto-correlation mode. For the optimal case of BINGO with no foregrounds, the combination of the HI angular power spectra with Planck results allows w to be measured with a precision of 4%, while the combination of the BAO acoustic scale with Planck gives a precision of 7%. We consider a number of potentially complicating effects, including foregrounds and redshift dependent bias, which increase the uncertainty on w but not dramatically; in all cases the final uncertainty is found to be less than 8% for BINGO. For the combination of SKA-MID in auto-correlation mode (total-power) with Planck, we find that, in ideal conditions, w can be measured with a precision of 4% for the redshift range 0.35 <z <3 (350 - 1050 MHz) and 2% for 0 <z <0.49 (950 - 1421 MHz). Extending the model to include the sum of neutrino masses yields a 95% upper limit of less than 0.30 eV for BINGO and less than 0.12 eV for SKA phase 1, competitive with the current best constraints in the case of BINGO and significantly better in the case of SKA.
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Van, De Rijt Nicolas. "Signatures of the primordial universe in large-scale structure surveys." Palaiseau, Ecole polytechnique, 2012. http://pastel.archives-ouvertes.fr/docs/00/72/78/11/PDF/PhDthesis.pdf.
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L'étude des grandes structures de l'Univers est un des meilleurs moyens pour comprendre l'origine et l'évolution de l'Univers. Dans cette thèse, nous nous spécialisons aussi bien dans la théorie des perturbations aux échelles cosmologiques, que dans le cisaillement cosmique. La théorie des perturbations aux échelles cosmologiques décrit comment les grandes structures de l'Univers se sont formées à partir des minuscules fluctuations primordiales. Cette évolution est généralement décrite en se servant des équations du mouvement d'un fluide, et dans cette thèse nous introduisons quelques nouvelles versions de cette hiérarchie de Boltzmann. Les avantages et inconvénients de ces nouvelles hiérarchies sont analysés en détail. Nous introduisons aussi une nouvelle technique, appelée l'approximation eikonal, qui nous permet de mieux comprendre les résultats des autres approches utilisées en théorie des perturbations. En outre, grâce à sa généralité, elle nous permet de généraliser une grande quantité de résultats. Le cisaillement cosmique décrit comment l'effet des lentilles gravitationnelles déforme notre image du ciel. Dans cette thèse, nous étudions de manière détaillée le bispectre du cisaillement cosmique, au deuxième ordre en les potentiels gravitationnels. Le calcul est intégralement fait en "full sky", généralisant ainsi les résultats existants. Pour simplifier les calculs numériques, nous introduisons et généralisons l'approximation dite de LimberThe study of the large-scale structure of the Universe is one of the most important tools used to understand the origin and evolution of the Universe. In this thesis, we focus on two different facets of this study: cosmological perturbation theory and cosmic shear. Cosmological perturbation theory describes how the large-scale structure of the Universe has been created out of the tiny initial perturbations. This evolution is described using fluid equations, and in this thesis, we introduce new versions of this Boltzmann hierarchy. The advantages and disadvantages of each hierarchy are thoroughly analysed. We also introduce a novel technique, dubbed the eikonal approximation, which enables us to better understand the results of existing perturbation theory approaches. Moreover, its broad range of applicability allows us to generalise many results. Cosmic shear describes how gravitational lensing deforms the image of the sky. In this thesis, we compute in great detail the bispectrum of cosmic shear to second order in the gravitational potentials. The complete calculation is done on the full sky, making the results much more general than the existing ones. To ease the otherwise impossible numerical calculations, we introduce the (extended) Limber approximation
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Leaf, Kyle, and Fulvio Melia. "A two-point diagnostic for the H ii galaxy Hubble diagram." OXFORD UNIV PRESS, 2018. http://hdl.handle.net/10150/627132.
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A previous analysis of starburst-dominated HII galaxies and HII regions has demonstrated a statistically significant preference for the Friedmann-Robertson-Walker cosmology with zero active mass, known as the R-h = c(t) universe, over Lambda cold dark matter (Lambda CDM) and its related dark-matter parametrizations. In this paper, we employ a two-point diagnostic with these data to present a complementary statistical comparison of Rh = ct with Planck Lambda CDM. Our two-point diagnostic compares, in a pairwise fashion, the difference between the distance modulus measured at two redshifts with that predicted by each cosmology. Our results support the conclusion drawn by a previous comparative analysis demonstrating that Rh = ct is statistically preferred over Planck Lambda CDM. But we also find that the reported errors in the HII measurements may not be purely Gaussian, perhaps due to a partial contamination by non-Gaussian systematic effects. The use of HII galaxies and HII regions as standard candles may be improved even further with a better handling of the systematics in these sources.
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Kwan, J., C. Sánchez, J. Clampitt, J. Blazek, M. Crocce, B. Jain, J. Zuntz, et al. "Cosmology from large-scale galaxy clustering and galaxy–galaxy lensing with Dark Energy Survey Science Verification data." OXFORD UNIV PRESS, 2017. http://hdl.handle.net/10150/623270.
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We present cosmological constraints from the Dark Energy Survey (DES) using a combined analysis of angular clustering of red galaxies and their cross-correlation with weak gravitational lensing of background galaxies. We use a 139 deg(2) contiguous patch of DES data from the Science Verification (SV) period of observations. Using large-scale measurements, we constrain the matter density of the Universe as Omega(m) = 0.31 +/- 0.09 and the clustering amplitude of the matter power spectrum as sigma(8) = 0.74 +/- 0.13 after marginalizing over seven nuisance parameters and three additional cosmological parameters. This translates into S-8 = sigma(8)(Omega(m)/0.3)(0.16) = 0.74 +/- 0.12 for our fiducial lens redshift bin at 0.35 < z < 0.5, while S-8 = 0.78 +/- 0.09 using two bins over the range 0.2 < z < 0.5. We study the robustness of the results under changes in the data vectors, modelling and systematics treatment, including photometric redshift and shear calibration uncertainties, and find consistency in the derived cosmological parameters. We show that our results are consistent with previous cosmological analyses from DES and other data sets and conclude with a joint analysis of DES angular clustering and galaxy-galaxy lensing with Planck Cosmic Microwave Background data, baryon accoustic oscillations and Supernova Type Ia measurements.
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Marcondes, Rafael José França. "Interacting dark energy models in Cosmology and large-scale structure observational tests." Universidade de São Paulo, 2016. http://www.teses.usp.br/teses/disponiveis/43/43134/tde-17102016-123725/.
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Modern Cosmology offers us a great understanding of the universe with striking precision, made possible by the modern technologies of the newest generations of telescopes. The standard cosmological model, however, is not absent of theoretical problems and open questions. One possibility that has been put forward is the existence of a coupling between dark sectors. The idea of an interaction between the dark components could help physicists understand why we live in an epoch of the universe where dark matter and dark energy are comparable in terms of energy density, which can be regarded as a strange coincidence given that their time evolutions are completely different. Dark matter and dark energy are generally treated as perfect fluids. Interaction is introduced when we allow for a non-zero term in the right-hand side of their individual energy-momentum tensor conservation equations. We proceed with a phenomenological approach to test models of interaction with observations of redshift-space distortions. In a flat universe composed only of these two fluids, we consider separately two forms of interaction, through terms proportional to the densities of both dark energy and dark matter. An analytic expression for the growth rate approximated as f = Omega^gamma, where Omega is the percentage contribution from the dark matter to the energy content of the universe and gamma is the growth index, is derived in terms of the interaction strength and of other parameters of the model in the first case, while for the second model we show that a non-zero interaction cannot be accommodated by the index growth approximation. The successful expressions obtained are then used to compare the predictions with growth of structure observational data in a Markov Chain Monte Carlo code and we find that the current growth data alone cannot impose constraints on the interaction strength due to their large uncertainties. We also employ observations of galaxy clusters to assess their virial state via the modified Layzer-Irvine equation in order to detect signs of an interaction. We obtain measurements of observed virial ratios, interaction strength, rest virial ratio and departure from equilibrium for a set of clusters. A compounded analysis indicates an interaction strength of 0.29^{+2.25}_{-0.40}, compatible with no interaction, but a compounded rest virial ratio of 0.82^{+0.13}_{-0.14}, which means a 2 sigma confidence level detection. Despite this tension, the method produces encouraging results while still leaves room for improvement, possibly by removing the assumption of small departure from equilibrium.A cosmologia moderna oferece um ótimo entendimento do universo com uma precisão impressionante, possibilitada pelas tecnologias modernas das gerações mais novas de telescópios. O modelo cosmológico padrão, porém, não é livre de problemas do ponto de vista teórico, deixando perguntas ainda sem respostas. Uma possibilidade que tem sido proposta é a existência de um acoplamento entre setores escuros. A ideia de uma interação entre os componentes escuros poderia ajudar os físicos a entender por que vivemos em uma época do universo na qual a matéria escura e a energia escura são comparáveis em termos de densidades de energia, o que pode ser considerado uma estranha coincidência dado que suas evoluções com o tempo são completamente diferentes. Matéria escura e energia escura são geralmente tratadas como fluidos perfeitos. A interação é introduzida ao permitirmos um tensor não nulo no lado direito das equações de conservação dos tensores de energia-momento. Prosseguimos com uma abordagem fenomenológica para testar modelos de interação com observações de distorções no espaço de redshift. Em um universo plano composto apenas por esses dois fluidos, consideramos, separadamente, duas formas de interação, através de termos proporcionais às densidades de energia escura e de matéria escura. Uma expressão analítica para a taxa de crescimento aproximada por f = Omega^gamma, onde Omega é a contribuição percentual da matéria escura para o conteúdo do universo e gamma é o índice de crescimento, é deduzida em termos da interação e de outros parâmetros do modelo no primeiro caso, enquanto para o segundo caso mostramos que uma interação não nula não pode ser acomodada pela aproximação do índice de crescimento. As expressões obtidas são então utilizadas para comparar as previsões com dados observacionais de crescimento de estruturas em um programa para Monte Carlo via cadeias de Markov. Concluímos que tais dados atuais por si só não são capazes de restringir a interação devido às suas grandes incertezas. Utilizamos também observações de aglomerados de galáxias para analisar seus estados viriais através da equação de Layzer-Irvine modificada a fim de detectar sinais de interação. Obtemos medições de taxas viriais observadas, constante de interação, taxa virial de equilíbrio e desvio do equilíbrio para um conjunto de aglomerados. Uma análise combinada indica uma constante de interação 0.29^{+2.25}_{-0.40}, compatível com zero, mas uma taxa virial de equilíbrio combinada de 0.82^{+0.13}_{-0.14}, o que significa uma detecção em um intervalo de confiança de 2 sigma. Apesar desta tensão, o método produz resultados encorajadores enquanto ainda permite melhorias, possivelmente pela remoção da suposição de pequenos desvios do equilíbrio.
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Baxter, Eric J., Eduardo Rozo, Bhuvnesh Jain, Eli Rykoff, and Risa H. Wechsler. "Constraining the mass–richness relationship of redMaPPer clusters with angular clustering." OXFORD UNIV PRESS, 2016. http://hdl.handle.net/10150/622071.
Full textAbstract:
The potential of using cluster clustering for calibrating the mass-richness relation of galaxy clusters has been recognized theoretically for over a decade. Here, we demonstrate the feasibility of this technique to achieve high-precision mass calibration using redMaPPer clusters in the Sloan Digital Sky Survey North Galactic Cap. By including cross-correlations between several richness bins in our analysis, we significantly improve the statistical precision of our mass constraints. The amplitude of the mass-richness relation is constrained to 7 per cent statistical precision by our analysis. However, the error budget is systematics dominated, reaching a 19 per cent total error that is dominated by theoretical uncertainty in the bias-mass relation for dark matter haloes. We confirm the result from Miyatake et al. that the clustering amplitude of redMaPPer clusters depends on galaxy concentration as defined therein, and we provide additional evidence that this dependence cannot be sourced by mass dependences: some other effect must account for the observed variation in clustering amplitude with galaxy concentration. Assuming that the observed dependence of redMaPPer clustering on galaxy concentration is a form of assembly bias, we find that such effects introduce a systematic error on the amplitude of the mass-richness relation that is comparable to the error bar from statistical noise. The results presented here demonstrate the power of cluster clustering for mass calibration and cosmology provided the current theoretical systematics can be ameliorated.
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Ilić, Stéphane. "The large scale structures. A window on the dark components of the Universe." Thesis, Paris 11, 2013. http://www.theses.fr/2013PA112243/document.
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L'énergie sombre est l'un des grands mystères de la cosmologie moderne, responsable de l'actuelle accélération de l'expansion de notre Univers. Son étude est un des axes principaux de ma thèse : une des voies que j'exploite s'appuie sur la structuration de l'Univers à grande échelle à travers un effet observationnel appelé effet Sachs-Wolfe intégré (iSW). Cet effet est théoriquement détectable dans le fond diffus cosmologique (FDC) : avant de nous parvenir cette lumière traverse un grand nombre grandes structures sous-tendues par des potentiels gravitationnels. L'accélération de l'expansion étire et aplatit ces potentiels pendant le passage des photons du FDC, modifiant leur énergie d'une façon dépendante des caractéristiques de l'énergie sombre. L'effet iSW n'a qu'un effet ténu sur le FDC, obligeant l'utilisation de données externes pour le détecter. Une approche classique consiste à corréler le FDC avec un traceur de la distribution de la matière, et donc des potentiels sous-jacents. Maintes fois tentée avec des relevés de galaxies, cette corrélation n'a pas donné à l'heure actuelle de résultat définitif sur la détection de l'effet iSW, la faute à des relevés pas assez profonds et/ou avec une couverture trop faible. Un partie de ma thèse est dédiée à la corrélation du FDC avec un autre fond "diffus" : le fond diffus infrarouge (FDI), qui est constitué de l'émission intégrée des galaxies lointaines non-résolues. J'ai pu montrer qu'il représente un excellent traceur, exempt des défauts des relevés actuels. Les niveaux de signifiance attendus pour la corrélation CIB-CMB excèdent ceux des relevés actuels, et rivalisent avec ceux prédits pour la futur génération de très grands relevés. Dans la suite, ma thèse a porté sur l'empreinte individuelle sur le FDC des plus grandes structures par effet iSW. Mon travail sur le sujet a d'abord consisté à revisiter une étude précédente d'empilement de vignettes de FDC à la position de structures, avec mes propres protocole de mesure et tests statistiques pour vérifier la signifiance de ces résultats, délicate à évaluer et sujette à de possibles biais de sélection. J'ai poursuivi en appliquant cette même méthode de détection à d'autres catalogues de structures disponibles, beaucoup plus conséquents et supposément plus raffinés dans leur algorithme de détection. Les résultats pour un d'eux suggère la présence d'un signal à des échelles et amplitudes compatible avec la théorie, mais à des niveaux modérés de signifiance. Ces résultats empilements font s'interroger concernant le signal attendu : cela m'a amené à travailler sur une prédiction théorique de l'iSW engendré par des structures, par des simulations basées sur la métrique de Lemaître-Tolman-Bondi. Cela m'a permis de prédire l'effet iSW théorique exact de structures existantes : l'amplitude centrale des signaux mesurés est compatible avec la théorie, mais présente des caractéristiques non-reproductibles par ces mêmes prédictions. Une extension aux catalogues étendus permettra de vérifier la signifiance de leurs signaux et leur compatibilité avec la théorie. Un dernier pan de ma thèse porte sur une époque de l'histoire de l'Univers appelée réionisation : son passage d'un état neutre à ionisé par l'arrivée des premières étoiles et autres sources ionisantes. Cette période a une influence importante sur le FDC et ses propriétés statistiques, en particulier sur son spectre de puissance des fluctuations de polarisation. Dans mon cas, je me suis penché sur l'utilisation des mesures de températures du milieu intergalactique, afin d'étudier la contribution possible de la désintégration et annihilation de l'hypothétique matière sombre. A partir d'un travail théorique sur plusieurs modèles et leur comparaison aux observations de température, j'ai pu extraire des contraintes intéressantes et inédites sur les paramètres cruciaux de la matière sombre et des caractéristiques cruciales de la réionisation elle-mêmeThe dark energy is one of the great mysteries of modern cosmology, responsible for the current acceleration of the expansion of our Universe. Its study is a major focus of my thesis : the way I choose to do so is based on the large-scale structure of the Universe, through a probe called the integrated Sachs-Wolfe effect (iSW). This effect is theoretically detectable in the cosmic microwave background (CMB) : before reaching us this light travelled through large structures underlain by gravitational potentials. The acceleration of the expansion stretches and flattens these potentials during the crossing of photons, changing their energy, in a way that depend on the properties of the dark energy. The iSW effect only has a weak effect on the CMB requiring the use of external data to be detectable. A conventional approach is to correlate the CMB with a tracer of the distribution of matter, and therefore the underlying potentials. This has been attempted numerous times with galaxies surveys but the measured correlation has yet to give a definitive result on the detection of the iSW effect. This is mainly due to the shortcomings of current surveys that are not deep enough and/or have a too low sky coverage. A part of my thesis is devoted to the correlation of FDC with another diffuse background, namely the cosmological infrared background (CIB), which is composed of the integrated emission of the non-resolved distant galaxies. I was able to show that it is an excellent tracer, free from the shortcomings of current surveys. The levels of significance for the expected correlation CIB-CMB exceed those of current surveys, and compete with those predicted for the future generation of very large surveys. In the following, my thesis was focused on the individual imprint in the CMB of the largest structures by iSW effect. My work on the subject first involved revisiting a past study of stacking CMB patches at structures location, using my own protocol, completed and associated with a variety of statistical tests to check the significance of these results. This point proved to be particularly difficult to assess and subject to possible selection bias. I extended the use of this detection method to other available catalogues of structures, more consequent and supposedly more sophisticated in their detection algorithms. The results from one of them suggests the presence of a signal at scales and amplitude consistent with the theory, but with moderate significance. The stacking results raise questions regarding the expected signal : this led me to work on a theoretical prediction of the iSW effect produced by structures, through simulations based on the Lemaître-Tolman-Bondi metric. This allowed me to predict the exact theoretical iSW effect of existing structures. The central amplitude of the measured signals is consistent with the theory, but shows features non-reproducible by my predictions. An extension to the additional catalogues will verify the significance of their signals and their compatibility with the theory. Another part of my thesis focuses on a distant time in the history of the Universe, called reionisation : the transition from a neutral universe to a fully ionised one under the action of the first stars and other ionising sources. This period has a significant influence on the CMB and its statistical properties, in particular the power spectrum of its polarisation fluctuations. In my case, I focused on the use of temperature measurements of the intergalactic medium during the reionisation in order to investigate the possible contribution of the disintegration and annihilation of the hypothetical dark matter. Starting from a theoretical work based on several models of dark matter, I computed and compared predictions to actual measures of the IGM temperature, which allowed me to extract new and interesting constraints on the critical parameters of the dark matter and crucial features of the reionisation itself
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Comparat, Johan. "Baryonic acoustic oscillations with emission line galaxies at intermediate redshift : the large-scale structure of the universe." Thesis, Aix-Marseille, 2013. http://www.theses.fr/2013AIXM4720/document.
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J'ai démontrer la faisabilité de la sélection de la cible pour les galaxies en ligne des émissions lumineuses. Je comprends maintenant les principaux mécanismes physiques de conduite de l'efficacité d'une sélection, en particulier le rapport à la photométrie de parent. Une question reste perplexe, je ne pouvais pas encore estimer quantitativement l'impact de la poussière sur l'efficacité de la sélection. J'espère que d'aborder cette question avec l'ensemble des données décrites dans le chapitre 4.En dehors de la ligne de sélection de la cible de la galaxie d'émission, j'ai étudié, au premier ordre, les deux principales erreurs systématiques sur la détermination de l'échelle BAO nous attendent en raison de l'utilisation galaxies en ligne des émissions comme traceurs de la question. J'ai d'abord montré le caractère incomplet de la distribution redshift, en raison de la mesure du décalage spectral avec [Oii], est lié à la résolution instrumentale. Je trouve qu'il ya deux régimes intéressants. Pour une observation des plus brillants [OII] émetteurs, une résolution modérée est suffisante, alors que pour une enquête plus faible, la plus haute de la résolution le meilleur. Deuxièmement, j'ai estimé le biais de la galaxie linéaire des sélections discuté avant et je trouve qu'ils sont très biaisés. D'une part, ce sont d'excellentes nouvelles pour les observateurs, comme le temps nécessaire pour observer à un signal donné au bruit dans le spectre de puissance diminue avec le carré de la partialité. D'autre part, elle constitue un nouveau défi pour les algorithmes de reconstruction et la fabrication de catalogues simulacresIn this PhD, I demonstrate the feasibility of the target selection for bright emission line galaxies. Also I now understand the main physical mechanisms driving the efficiency of a selection, in particular the relation to the parent photometry. A puzzling issue remains, I could not yet estimate quantitatively the impact of the dust on the selection efficiency. I hope to address this question with the data set described in chapter 4.Apart from the emission line galaxy target selection, I investigated, at first order, the two main systematic errors on the determination of the BAO scale we expect due to using emission line galaxies as tracers of the matter. First I showed the incompleteness in the redshift distribution, due to the measurement of the redshift with [Oii], is related to the instrumental resolution. I find there are two interesting regimes. For an observation of the brightest [Oii]emitters, a moderate resolution is sufficient, whereas for a fainter survey, the highest the resolution the best. Secondly, I estimated the linear galaxy bias of the selections discussed before and I find they are highly biased. On one hand, this is great news for the observers, as the time required to observed at a given signal to noise in the power spectrum decreases with the square of the bias. On the other hand, it constitutes a new challenge for reconstruction algorithms and the making of mock catalogs. The work in progress described in the last chapter shows I am starting to try and handle these questions in a robust manner
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Sánchez, C., J. Clampitt, A. Kovacs, B. Jain, J. García-Bellido, S. Nadathur, D. Gruen, et al. "Cosmic voids and void lensing in the Dark Energy Survey Science Verification data." OXFORD UNIV PRESS, 2017. http://hdl.handle.net/10150/623046.
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Cosmic voids are usually identified in spectroscopic galaxy surveys, where 3D information about the large-scale structure of the Universe is available. Although an increasing amount of photometric data is being produced, its potential for void studies is limited since photometric redshifts induce line-of-sight position errors of >= 50 Mpc h(-1)which can render many voids undetectable. We present a new void finder designed for photometric surveys, validate it using simulations, and apply it to the high-quality photo-z redMaGiC galaxy sample of the DES Science Verification data. The algorithm works by projecting galaxies into 2D slices and finding voids in the smoothed 2D galaxy density field of the slice. Fixing the line-of-sight size of the slices to be at least twice the photo-z scatter, the number of voids found in simulated spectroscopic and photometric galaxy catalogues is within 20 per cent for all transverse void sizes, and indistinguishable for the largest voids (R-v >= 70 Mpc h(-1)). The positions, radii, and projected galaxy profiles of photometric voids also accurately match the spectroscopic void sample. Applying the algorithm to the DES-SV data in the redshift range 0.2 < z < 0.8, we identify 87 voids with comoving radii spanning the range 18-120 Mpc h(-1), and carry out a stacked weak lensing measurement. With a significance of 4.4 sigma, the lensing measurement confirms that the voids are truly underdense in the matter field and hence not a product of Poisson noise, tracer density effects or systematics in the data. It also demonstrates, for the first time in real data, the viability of void lensing studies in photometric surveys.
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Ilic, Stéphane. "The large scale structures. a window on the Dark components of the Universe." Phd thesis, Université Paris Sud - Paris XI, 2013. http://tel.archives-ouvertes.fr/tel-00933818.
Full textAbstract:
The dark energy is one of the great mysteries of modern cosmology, responsible for the current acceleration of the expansion of our Universe. Its study is a major focus of my thesis : the way I choose to do so is based on the large-scale structure of the Universe, through a probe called the integrated Sachs-Wolfe effect (iSW). This effect is theoretically detectable in the cosmic microwave background (CMB) : before reaching us this light travelled through large structures underlain by gravitational potentials. The acceleration of the expansion stretches and flattens these potentials during the crossing of photons, changing their energy, in a way that depend on the properties of the dark energy. The iSW effect only has a weak effect on the CMB requiring the use of external data to be detectable. A conventional approach is to correlate the CMB with a tracer of the distribution of matter, and therefore the underlying potentials. This has been attempted numerous times with galaxies surveys but the measured correlation has yet to give a definitive result on the detection of the iSW effect. This is mainly due to the shortcomings of current surveys that are not deep enough and/or have a too low sky coverage. A part of my thesis is devoted to the correlation of FDC with another diffuse background, namely the cosmological infrared background (CIB), which is composed of the integrated emission of the non-resolved distant galaxies. I was able to show that it is an excellent tracer, free from the shortcomings of current surveys. The levels of significance for the expected correlation CIB-CMB exceed those of current surveys, and compete with those predicted for the future generation of very large surveys. In the following, my thesis was focused on the individual imprint in the CMB of the largest structures by iSW effect. My work on the subject first involved revisiting a past study of stacking CMB patches at structures location, using my own protocol, completed and associated with a variety of statistical tests to check the significance of these results. This point proved to be particularly difficult to assess and subject to possible selection bias. I extended the use of this detection method to other available catalogues of structures, more consequent and supposedly more sophisticated in their detection algorithms. The results from one of them suggests the presence of a signal at scales and amplitude consistent with the theory, but with moderate significance. The stacking results raise questions regarding the expected signal : this led me to work on a theoretical prediction of the iSW effect produced by structures, through simulations based on the Lemaître-Tolman-Bondi metric. This allowed me to predict the exact theoretical iSW effect of existing structures. The central amplitude of the measured signals is consistent with the theory, but shows features non-reproducible by my predictions. An extension to the additional catalogues will verify the significance of their signals and their compatibility with the theory. Another part of my thesis focuses on a distant time in the history of the Universe, called reionisation : the transition from a neutral universe to a fully ionised one under the action of the first stars and other ionising sources. This period has a significant influence on the CMB and its statistical properties, in particular the power spectrum of its polarisation fluctuations. In my case, I focused on the use of temperature measurements of the intergalactic medium during the reionisation in order to investigate the possible contribution of the disintegration and annihilation of the hypothetical dark matter. Starting from a theoretical work based on several models of dark matter, I computed and compared predictions to actual measures of the IGM temperature, which allowed me to extract new and interesting constraints on the critical parameters of the dark matter and crucial features of the reionisation itself
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Gnedin, Nickolay Y., George D. Becker, and Xiaohui Fan. "Cosmic Reionization on Computers: Properties of the Post-reionization IGM." IOP PUBLISHING LTD, 2017. http://hdl.handle.net/10150/624497.
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We present a comparison between several observational tests of the post-reionization intergalactic medium and the numerical simulations of reionization completed under the Cosmic Reionization On Computers (CROC) project. The CROC simulations match the gap distribution reasonably well, and also provide a good match for the distribution of peak heights, but there is a notable lack of wide peaks in the simulated spectra and the flux-probability distribution functions are poorly matched in the narrow redshift interval 5.5 < z < 5.7, with the match at other redshifts being significantly better, albeit not exact. Both discrepancies are related: simulations show more opacity than the data.
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Leaf, Kyle, and Fulvio Melia. "Analysing H(z) data using two-point diagnostics." OXFORD UNIV PRESS, 2017. http://hdl.handle.net/10150/625514.
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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.
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Leistedt, B., H. V. Peiris, F. Elsner, A. Benoit-Lévy, A. Amara, A. H. Bauer, M. R. Becker, et al. "MAPPING AND SIMULATING SYSTEMATICS DUE TO SPATIALLY VARYING OBSERVING CONDITIONS IN DES SCIENCE VERIFICATION DATA." IOP PUBLISHING LTD, 2016. http://hdl.handle.net/10150/622062.
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Spatially varying depth and the characteristics of observing conditions, such as seeing, airmass, or sky background, are major sources of systematic uncertainties in modern galaxy survey analyses, particularly in deep multi-epoch surveys. We present a framework to extract and project these sources of systematics onto the sky, and apply it to the Dark Energy Survey (DES) to map the observing conditions of the Science Verification (SV) data. The resulting distributions and maps of sources of systematics are used in several analyses of DES-SV to perform detailed null tests with the data, and also to incorporate systematics in survey simulations. We illustrate the complementary nature of these two approaches by comparing the SV data with BCC-UFig, a synthetic sky catalog generated by forward-modeling of the DES-SV images. We analyze the BCC-UFig simulation to construct galaxy samples mimicking those used in SV galaxy clustering studies. We show that the spatially varying survey depth imprinted in the observed galaxy densities and the redshift distributions of the SV data are successfully reproduced by the simulation and are well-captured by the maps of observing conditions. The combined use of the maps, the SV data, and the BCC-UFig simulation allows us to quantify the impact of spatial systematics on N(z), the redshift distributions inferred using photometric redshifts. We conclude that spatial systematics in the SV data are mainly due to seeing fluctuations and are under control in current clustering and weak-lensing analyses. However, they will need to be carefully characterized in upcoming phases of DES in order to avoid biasing the inferred cosmological results. The framework presented here is relevant to all multi-epoch surveys and will be essential for exploiting future surveys such as the Large Synoptic Survey Telescope, which will require detailed null tests and realistic end-to-end image simulations to correctly interpret the deep, high-cadence observations of the sky.
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Freudenburg, Jenna Kay Cunliffe. "Precision Cosmology with Weak Gravitational Lensing and Galaxy Populations." The Ohio State University, 2020. http://rave.ohiolink.edu/etdc/view?acc_num=osu1595544137004009.
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More, Surhud, Hironao Miyatake, Masahiro Takada, Benedikt Diemer, Andrey V. Kravtsov, Neal K. Dalal, Anupreeta More, et al. "DETECTION OF THE SPLASHBACK RADIUS AND HALO ASSEMBLY BIAS OF MASSIVE GALAXY CLUSTERS." IOP PUBLISHING LTD, 2016. http://hdl.handle.net/10150/621397.
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We show that the projected number density profiles of Sloan Digital Sky Survey photometric galaxies around galaxy clusters display strong evidence for the splashback radius, a sharp halo edge corresponding to the location of the first orbital apocenter of satellite galaxies after their infall. We split the clusters into two subsamples with different mean projected radial distances of their members, < R-mem >, at fixed richness and redshift. The sample with smaller < R-mem > has a smaller ratio of the splashback radius to the traditional halo boundary R-200m than the subsample with larger < R-mem >, indicative of different mass accretion rates for these subsamples. The same subsamples were recently used by Miyatake et al. to show that their large-scale clustering differs despite their similar weak lensing masses, demonstrating strong evidence for halo assembly bias. We expand on this result by presenting a 6.6 sigma difference in the clustering amplitudes of these samples using cluster-photometric galaxy cross-correlations. This measurement is a clear indication that halo clustering depends on parameters other than halo mass. If < R-mem > is related to the mass assembly history of halos, the measurement is a manifestation of the halo assembly bias. However, our measured splashback radii are smaller, while the strength of the assembly bias signal is stronger, than the predictions of collisionless. cold dark matter simulations. We show that dynamical friction, cluster mis-centering, or projection effects are not likely to be the sole source of these discrepancies. However, further investigations regarding unknown catastrophic weak lensing or cluster identification systematics are warranted.
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Zeng, Houdun, Fulvio Melia, and Li Zhang. "Cosmological tests with the FSRQ gamma-ray luminosity function." OXFORD UNIV PRESS, 2016. http://hdl.handle.net/10150/621735.
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The extensive catalogue of gamma-ray selected flat-spectrum radio quasars (FSRQs) produced by Fermi during a four-year survey has generated considerable interest in determining their gamma-ray luminosity function (GLF) and its evolution with cosmic time. In this paper, we introduce the novel idea of using this extensive database to test the differential volume expansion rate predicted by two specific models, the concordance Lambda cold darkmatter (Lambda CDM) and R-h = ct cosmologies. For this purpose, we use two well-studied formulations of the GLF, one based on pure luminosity evolution (PLE) and the other on a luminosity-dependent density evolution (LDDE). Using a Kolmogorov-Smirnov test on one-parameter cumulative distributions (in luminosity, redshift, photon index and source count), we confirm the results of earlier works showing that these data somewhat favour LDDE over PLE; we show that this is the case for both Lambda CDM and R-h = ct. Regardless of which GLF one chooses, however, we also show that model selection tools very strongly favour R-h = ct over Lambda CDM. We suggest that such population studies, though featuring a strong evolution in redshift, may none the less be used as a valuable independent check of other model comparisons based solely on geometric considerations.
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Fromont, Paul de. "Cosmologie et gravité des régions sphériques compensées." Thesis, Sorbonne Paris Cité, 2017. http://www.theses.fr/2017USPCC148/document.
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Cette thèse de cosmologie est consacrée à l'étude de l'empreinte de l'énergie noire sur la formation des structures de l'Univers. Je défini et introduit les régions cosmiques compensées comme l'environnement à grande échelle autour des extrema locaux dans le champ de densité. Dans le cas d'un minimum central, cette région peut être identifiée aux vides cosmiques usuels. A l'aide de simulations numériques, je montre que ces régions présentent des propriétés de formes particulières et qu'elles dépendent de la cosmologie. Je montre que la forme moyenne de ces profils de densité ainsi que leur propriétés statistiques peuvent être calculée analytiquement dans l'Univers primordial. En utilisant une dynamique appropriée, je montre qu'il est possible de suivre précisément l'évolution non linéaire de ces structures. Il devient alors possible de reconstruire les profils de matières observés aujourd'hui à partir les profils théoriques primordiaux évolués selon une dynamique appropriée. J’exhibe une propriété fondamentale de ces régions qui maintient constant une taille particulière, le rayon de compensation. Autour de ce point, l'évolution non linéaire du champ de matière peut être suivie analytiquement. En étudiant l'effondrement gravitationnel dans des théories étendues de gravité, je montre qu'il est possible de contraindre efficacement la nature de la gravité et de la cosmologie à partir de l'étude de certaines propriétés spécifiques à ces régions. Ce travail permet à la fois de donner une origine aux profils de matière sur les très grandes échelles cosmiques mais aussi de définir de nouvelles sondes cosmologiques pour tester la nature de notre UniversThis thesis is devoted to the study of the imprints of dark energy on the formation of the large scale structures in the Universe. I define the spherically compensated cosmic regions as the large-scale environment around local extrema in the density field. For central minimum, this region can be identified with standard cosmic voids. Using numerical simulations, I show that these regions, once properly identified, can be used efficiently to distinguish competitive cosmological models. I show that the average shape of these density profiles and their statistical properties can be analytically computed in the primordial Universe. Using an appropriate dynamical formalism, I show that it is possible to follow the nonlinear evolution of these structures until today. This allows to reconstruct the shape of such large scale regions from first principles. I exhibit a fundamental property of these regions which maintains constant a particular size : the compensation radius. Around this radius, the nonlinear evolution of the matter field can be analytically derived. By studying the gravitational collapse in gravity models beyond General Relativity, I show that it is possible to constrain efficiently both cosmology and the nature of gravity. Beside giving a physically motivated model for both shape and statistical properties of such large scale matter profile, this work also define new cosmological probes that could be used to test the nature of our Universe
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Rubira, Henrique. "Melhorias na predição da estrutura de larga escala do universo por meio de teorias efetivas de campo." Universidade de São Paulo, 2018. http://www.teses.usp.br/teses/disponiveis/43/43134/tde-08102018-145202/.
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Com os próximos grandes projetos the observação do Universo, a cosmologia entrará em uma era de alta precisão de medidas. Novos dados trarão um novo entendimento da evolução do Universo, seus principais componentes e do comportamento da gravi- dade. Sendo assim, é fundamental também ter uma boa predição teórica para a formação de estrutura de larga escala em regime não-linear. A melhor maneira de resolver as equações hidrodinâmicas que descrevem o nosso universo é por meio de simulações cosmológicas na rede. Entretando, estas contém desafios, como a correta inclusão de física bariônica e a diminuição do alto tempo computacional. Uma outra abordagem muito usada é o cálculo das funções de cor- relação por meio de métodos perturbativos (em inglês, Standard Perturbation Theory, ou SPT). Entretanto, esta contém problemas variados: pode não convergir para algu- mas cosmologias e, caso convirja, não há certeza de convergência para o resultado correto. Além disso, há uma escala privilegiada nos limites integrais que envolvem o método perturbativo. Nós calculamos o resultado por esse método até terceira ordem e mostramos que o termo de terceira ordem é ainda maior que o de 2-loops e 3-loops. Isso evidencia alguns problemas descritos com o método perturbativo. O método de Teorias Efetivas de Campo aplicado ao estudo de LSS busca corrigir os problemas da SPT e, desta forma, complementar os resultados de simulações na rede. Em outras áreas da física, como a Cromodinâmica Quântica de baixas energias, EFTs também são usadas como um complemento a essas simulações na rede. EFTs melhoram a predição do espectro de potência da matéria por meio da inclusão dos chamados contra-termos, que precisam ser fitados em simulações. Estes contratermos, que são parâmetros livres, contém importante informação sobre como a física em pequenas escalas afeta a física nas escalas de interesse. Explicaremos os resultados para a predição em 3-loops de EFT, trabalho inédito. É possível usar as EFTs também no problema de conectar a campo de matéria com outros traçadores, como os halos e as galáxias, chamado de bias. Com as EFTs podemos construir uma base completa de operadores para parametrizar o bias. Será explicado como utilizar esses operadores para melhorar a predição do bias em escalas não-lineares. Serão calculados esses termos de EFT em simulações. Também será mostrado como renormalizar o bias em coordenadas de Lagrange. Por fim, será explicada outra importante aplicação das EFTs em cosmologia, mais especificamente em teorias de inflação. EFTs parametrizam desvios nas teorias de um campo único no chamado regime de slow-roll.With future cosmological surveys, cosmology will enter in the precision era. New data will improve the constraints on the standard cosmological model enhancing our knowledge about the universe history, its components and the behavior of gravity. In this context, it is vital to come up with precise theoretical predictions for the formation of large-scale structure beyond the linear regime. The best way of solving the fluid equations that describe the large-scale universe is through lattice simulations, which faces difficulties in the inclusion of accurate baryonic physics and is very computationally costly. Another approach is the theoreti- cal calculation of the correlation statistics through the perturbative approach, called Standard Perturbation Theory (SPT). However, SPT has several problems: for some cosmologies, it may not converge and even when it converges, we cannot be sure it converges to the right result. Also, it contains a special scale that is the loop momenta upper-bound in the integral. In this work, we show results for the 3-loop calculation. The term of third order is larger than the terms of 2-loops and 3-loops, making explicit SPT problems. In this work, we describe the recent usage of Effective Field Theories (EFTs) on Large Scale Structure problems to correct SPT issues and complement cosmological simulations. EFTs are used in other areas of physics, such as low energy QCD, serving as a complement to lattice calculations. EFT improves the predictions for the matter power spectrum and bispectrum by adding counterterms that need to be fitted. The free parameters, instead of being a problem, bring relevant information about how the small-scale physics affects the scales for which we are trying to make statistical predictions. We show the calculation of the 3-loop EFT counterterms. EFTs are also used to explain main points connecting the matter density field with tracers like galaxies and halos. EFTs highlighted how to construct a complete basis of operators that parametrize the bias. We explain how we can use EFT to improve the bias prediction to non-linear scales. We compute the non-linear halo-bias by fitting the bias parameters in simulations. We also show the EFT renormalization in Lagrangian coordinates. Finally, we explain another critical EFT application to cosmology: in primordial physics. It can be used to parametrize deviations to the slow-roll theory within the inflationary paradigm.
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Laigle, Clotilde. "Observational and theoretical constraints on galaxy evolution at high redshift." Thesis, Paris 6, 2016. http://www.theses.fr/2016PA066343.
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Je présente dans cette thèse de nouvelles contraintes sur la formation et l’évolution des galaxies, en étudiant leur croissance en masse et leur évolution au sein de la toile cosmique depuis l’époque de leur formation jusqu’à maintenant. Pour cela, j’ai créé un catalogue photométrique sur le champ COSMOS. Ce catalogue permet de sonder avec précision l’Univers à haut redshift. J’analyse ce relevé observé à l’aide de relevés virtuels, produits à partir de simulations hydrodynamiques. Ces simulations implémentent nos connaissances sur la formation et l’évolution des galaxies.Dans un premier temps, je montre que l’évolution en redshift des propriétés des galaxies est relativement bien comprise en invoquant des processus qui dépendent essentiellement de la masse, tels que le feedback des étoiles et des AGN. Je souligne également comment nos méthodes observationnelles génèrent des biais dans les propriétés physiques des galaxies calculées à partir de la photométrie.Dans un deuxième temps, je montre comment la dynamique des flots de matière à grande échelle gouverne l’acquisition du moment angulaire des galaxies et halos de matière noire, ce qui implique que certaines propriétés des galaxies sont supposées dépendre de leur environnement anisotrope. J’ai extrait la structure filamentaire du catalogue photométrique que j’ai créé sur le champ COSMOS et j’ai mesuré cette dépendance. Je trouve des gradients de masse et de couleurs dans la direction du filament. Il apparaît que la masse et le moment angulaire des galaxies sont deux quantités interdépendantes et tous deux impactés par leur environnement anisotropeI present in this thesis new constraints on galaxy formation and evolution while studying the galaxy mass growth and the co-evolution of the cosmic web and the embedded galaxies, from the epoch of cosmic dawn to today.To do so, I first created a new photometric catalog on the COSMOS field with precise photometric redshifts allowing to probe accurately the high-redshift Universe. I analyze this survey while relying heavily on comparisons with virtual galaxy surveys produced from state-of-the- art cosmological hydrodynamical simulations, which capture all our current knowledge of galaxy formation and evolution.From this comparative analysis, in the first part of my thesis I show that the redshift evolution of galaxy properties is reasonably well understood when invoking mass-dependent processes (AGN and stellar feed- back). I highlight also the effect of simplifying assumptions inherent to our observational methods, which bias the physical properties computed from galaxy photometry.Galaxies and haloes are embedded in the cosmic web, an intricate large-scale structure of walls, filaments and nodes. In the second part of my thesis, I show how galaxies and dark haloes gain their angular momentum from the large-scale flow, implying that some of their properties depend on their anisotropic filamentary environment. I then extract the filamentary structure from the observed photometric catalog and measure the dependence of galaxy properties to the anisotropic environment. I find mass and colour gradients towards the filaments. In turn it emerges that galaxy masses and angular momenta are two dependent quantities impacted by their anisotropic environment
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Petrie, Stephen. "Determining the characteristic mass of DLA host haloes from 21cm fluctuations." Connect to thesis, 2010. http://repository.unimelb.edu.au/10187/7159.
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Absorption profiles are found in the observed spectra from quasars, and the most prominent of these are the Damped Lyman-alpha Absorbers (DLAs). They are caused by large collections of neutral hydrogen (HI) gas, which are thought to be housed in galaxies that lie along the line-of-sight to quasars. HI gas associated with DLAs contains most of the HI gas in the Universe during 2 < z < 5, and hence details about DLAs are important for understanding the history of star formation, as well as the formation and evolution of galaxies. Wyithe (2008) proposed a method of determining the characteristic mass of dark matter haloes that host DLAs. This involves generating an analytic power spectrum of the fluctuations in 21cm brightness temperature caused by the HI gas in the Universe. Calculating this analytic 21cm power spectrum requires a formalism for the HI mass weighted clustering bias of DLAs on both large and small scales. We include this DLA clustering bias by firstly generating an analytic galaxy power spectrum using the halo model of Peacock & Smith (2000), as well as including the occupation of haloes by galaxies -- using the Halo Occupation Distribution (HOD) weighting of Peacock (2003). This weighting is then adapted to account for the occupation of haloes by HI gas.We then fit the analytic 21cm power spectrum generated using this formalism to a simulated 21cm power spectrum, with the characteristic mass of DLA host haloes being used as a fitting parameter. The DLA host halo mass is in turn dependent upon two parameters in our model: the minimum mass of haloes M_{min} included in our formalism, and the HI weighting index alpha_{HI}. The neutral hydrogen fraction is another parameter, which we can choose to be the same as that from our simulation volume. If we also choose a value for alpha_{HI} that is motivated by analysis of the dark matter and HI gas content of the haloes in the simulation, then we are able to fit the 21cm power spectrum at both large and small scales, with an M_{min} that is the same or similar to the lowest mass in the simulation's halo catalogue. This in turn gives a similar value for the DLA host halo mass that is known to be the case in the simulation. This demonstrates the viability of the Wyithe (2008) method for determining the DLA host halo mass using observations of 21cm fluctuations. However, degeneracies in the free parameters of our analytic formalism would hinder an accurate determination of the DLA host halo mass from actual future observations. This is due to the fact that the real space, spherically averaged 21cm power spectrum is used throughout this thesis. However, extending our analytic formalism to the redshift space, angular-dependent 21cm power spectrum should be capable of breaking the degeneracy between DLA host halo mass and neutral hydrogen fraction.
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Wibking, Benjamin Douglas. "Cosmic structure formation on small scales: From non-linear galaxy clustering to the interstellar medium." The Ohio State University, 2019. http://rave.ohiolink.edu/etdc/view?acc_num=osu1561556033289855.
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Pond, Jarrad W. T. "Perturbation analysis of fluctuations in the universe on large scales, including decaying solutions and rotational velocities." Honors in the Major Thesis, University of Central Florida, 2009. http://digital.library.ucf.edu/cdm/ref/collection/ETH/id/1309.
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This item is only available in print in the UCF Libraries. If this is your Honors Thesis, you can help us make it available online for use by researchers around the world by following the instructions on the distribution consent form at http://library.ucf.edu/Systems/DigitalInitiatives/DigitalCollections/InternetDistributionConsentAgreementForm.pdf You may also contact the project coordinator, Kerri Bottorff, at kerri.bottorff@ucf.edu for more information.Bachelors
Sciences
Physics
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Codis-Decara, Sandrine. "De la cosmologie à la formation des galaxies : que nous apprennent les grandes structures de l'Univers ?" Thesis, Paris 6, 2015. http://www.theses.fr/2015PA066343/document.
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Dans cette thèse sur articles, nous nous intéressons aux grandes structures de l’Univers et à leur rôle fondamental pour la cosmologie et la formation des galaxies. Les galaxies naissent et grandissent au sein des filaments de la toile cosmique soulevant la question de l’impact de ces filaments sur les propriétés galactiques telles que la morphologie. Pour étudier cette question fondamentale, nous allons dans un premier temps montrer que dans les simulations numériques de l’Univers, le spin des galaxies est fortement lié à la direction de leur filament hôte avec un comportement qui dépend de leur masse. Ces corrélations spin-filament seront expliquées qualitativement dans le contexte de la formation hiérarchique des structures cosmologiques. Un modèle analytique tenant compte de l’anisotropie de la toile cosmique complètera ce tableau en reproduisant les corrélations observées. Ces idées sont importantes pour comprendre la morphologie des galaxies mais aussi les alignements intrinsèques qui peuvent certaines sondes cosmologiques basées sur la mesure de l’astigmatisme cosmique. Nous allons en particulier mesurer cette contamination dans une simulation hydrodynamique. Dans la seconde partie de ce manuscrit, nous nous poserons la question de comment extraire efficacement de l’information de la toile cosmique en mesurant sa topologie et sa géométrie et en utilisant la théorie perturbative dans un régime quasi-linéaire, la pierre angulaire de ce travail reposant sur l’étude analytique de l’impact de l’effondrement non-linéaire des structures et des distorsions en espace des redshifts sur la statistique du champ de densité cosmiqueThis thesis by publication is devoted to the theoretical understanding of the large-scale structure of the Universe and its role in the context of cosmology and galaxy formation. The birth and evolution of galaxies occur within the large cosmic highways drawn by the cosmic web and the natural question which arises is whether galaxies retain a memory of the large-scale cosmic flows from which they emerge. To address this key question, we will first show that in cosmological simulations, the spin of galaxies and the direction of their host filament are correlated in a mass-dependent way. This signal will be shown to be qualitatively understood in the context of hierarchical structure formation. An analytic model which explicitly takes into account the anisotropy of the cosmic web will complement this qualitative understanding by reproducing the measured correlations. Those ideas are important to understand the evolution of galaxy morphology but also to understand the intrinsic alignments of galaxies that contaminate cosmological probes like cosmic shear experiments. We will in particular measure this contamination directly from a state-of-the-art hydrodynamical simulation. In a second part, we will address the question of how to efficiently use large-scale structure data to probe the cosmological model describing our Universe by measuring its topology and geometry and using perturbation theory in the weakly and even mildly non-linear regime. The major contribution of this work is to analytically study the effect of redshift space distortions and non-linear collapse of structures on the topology, geometry and statistics of the cosmic density field
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Dupuy, Alexandra. "Du HI radio à la mesure de la croissance des bassins gravitationnels." Thesis, Lyon, 2018. http://www.theses.fr/2018LYSE1201/document.
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Les mouvements des galaxies dans l'Univers sont causés par le tir à la corde qui a lieu entre l'expansion de l'univers et la gravitation. Cette rivalité a un impact sur la formation et la croissance des grandes structures de l'univers. Par conséquent, l'univers est plus ou moins compact selon le gagnant de ce duel. Dans ce contexte, cette thèse est divisée en trois parties, allant des observations à 21 cm à la mesure du taux de croissance actuel des grandes structures de l'univers et de la compacité de l'univers local.La collaboration Cosmicflows prépare des catalogues de distances de galaxies. Jusqu'à présent, trois catalogues ont été publiés, le dernier étant Cosmicflows-3. Cette thèse présente et analyse les données obtenues à partir d'observations à 21 cm. Ces nouvelles données seront utilisées pour former le prochain catalogue de distances Cosmicflows-4 à l'aide de la relation de Tully-Fisher, afin de corriger le manque de données dans l'hémisphère céleste Nord dans le catalogue actuel.À partir de la distance d'une galaxie, il est possible d'en déduire la partie radial de sa vitesse particulière, correspondant à la composante de sa vitesse totale causée par la gravitation. Les vitesses particulières des galaxies sont des sondes non-baisées de la matière et permettent d'extraire des informations sur les grandes structures de l'univers. Deux méthodologies utilisant les vitesses particulières ont été développées durant cette thèse pour caractériser les grandes structures de l'univers local.D'une part, les catalogues de vitesses particulières peuvent être utilisés pour reconstruire des champs de vitesse tridimensionnels. De tels champs de vitesse permettent de cartographier la structure de l'univers local et sont exploités dans cette thèse, à l'aide des lignes de flux, pour identifier des bassins et vallées gravitationnels dans l'univers local.D'autre part, une méthode basée sur l'analyse des corrélations à deux points des vitesses particulières des galaxies a été développée afin d'exhiber le taux de croissance actuel des grandes structures de l'univers local à partir de données observationnelles. Cette méthodologie est appliquée au catalogue observationnel de vitesses particulières Cosmicflows-3Motions of galaxies in the universe are due to the rivalry between the expansion of the universe and gravitation. This tug-of-war impacts the formation and the growth of large scale structures of the universe. Thus, depending on the identity of the winner of this duel, the universe is more or less compact. Within this context, this PhD thesis is divided into three parts, spanning from HI observations to the estimate of the growth of rate of large scale structures of the universe and the compactness of the local universe.The Cosmicflows collaboration assembles catalogues of galaxy distances. Up to now, three catalogues have been published, the last one being Cosmicflows-3. This thesis presents and analyses observational data obtained from HI observations. These new data will be used to construct the new compilation of distances Cosmicflows-4 by the use of the Tully-Fisher relation, in order to correct the lack of data in the Northern celestial hemisphere in the current catalog.From the distance of a galaxy, one can derive the radial part of its peculiar velocity corresponding to the component of its total velocity caused by gravitation. Peculiar velocities allow to probe the matter content of the universe and to extract information on large scale structures of the universe. Two methodologies using peculiar velocities have been developed during this thesis to characterize large scale structures of the local universe.On the one hand, peculiar velocity catalogues can be used to reconstruct tri-dimensional velocity fields. These velocity field allow one to map the structure of the local universe and are used in this thesis to identify gravitational basins and valleys within the local universe by computing streamlines.On the other hand, a method based on the analysis of two-point galaxy peculiar velocity correlations has been developed in order to constrain the growth rate of large scale structures of the local universe from observational data. This method is applied to the Cosmicflows-3 catalogue of observed peculiar velocities
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Kodi, Ramanah Doogesh. "Bayesian statistical inference and deep learning for primordial cosmology and cosmic acceleration." Thesis, Sorbonne université, 2019. http://www.theses.fr/2019SORUS169.
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Cette thèse a pour vocation le développement et l’application de nouvelles techniques d’inférence statistique bayésienne et d’apprentissage profond pour relever les défis statistiques imposés par les gros volumes de données complexes des missions du fond diffus cosmologique (CMB) ou des relevés profonds de galaxies de la prochaine génération, dans le but d'optimiser l’exploitation des données scientifiques afin d’améliorer, à terme, notre compréhension de l’Univers. La première partie de cette thèse concerne l'extraction des modes E et B du signal de polarisation du CMB à partir des données. Nous avons développé une méthode hiérarchique à haute performance, nommée algorithme du dual messenger, pour la reconstruction du champ de spin sur la sphère et nous avons démontré les capacités de cet algorithme à reconstruire des cartes E et B pures, tout en tenant compte des modèles de bruit réalistes. La seconde partie porte sur le développement d’un cadre d'inférence bayésienne pour contraindre les paramètres cosmologiques en s’appuyant sur une nouvelle implémentation du test géométrique d'Alcock-Paczyński et nous avons présenté nos contraintes cosmologiques sur la densité de matière et l'équation d'état de l'énergie sombre. Etant donné que le contrôle des effets systématiques est un facteur crucial, nous avons également présenté une fonction de vraisemblance robuste, qui résiste aux contaminations inconnues liées aux avant-plans. Finalement, dans le but de construire des émulateurs de dynamiques complexes dans notre modèle, nous avons conçu un nouveau réseau de neurones qui apprend à peindre des distributions de halo sur des champs approximatifs de matière noire en 3DThe essence of this doctoral research constitutes the development and application of novel Bayesian statistical inference and deep learning techniques to meet statistical challenges of massive and complex data sets from next-generation cosmic microwave background (CMB) missions or galaxy surveys and optimize their scientific returns to ultimately improve our understanding of the Universe. The first theme deals with the extraction of the E and B modes of the CMB polarization signal from the data. We have developed a high-performance hierarchical method, known as the dual messenger algorithm, for spin field reconstruction on the sphere and demonstrated its capabilities in reconstructing pure E and B maps, while accounting for complex and realistic noise models. The second theme lies in the development of various aspects of Bayesian forward modelling machinery for optimal exploitation of state-of-the-art galaxy redshift surveys. We have developed a large-scale Bayesian inference framework to constrain cosmological parameters via a novel implementation of the Alcock-Paczyński test and showcased our cosmological constraints on the matter density and dark energy equation of state. With the control of systematic effects being a crucial limiting factor for modern galaxy redshift surveys, we also presented an augmented likelihood which is robust to unknown foreground and target contaminations. Finally, with a view to building fast complex dynamics emulators in our above Bayesian hierarchical model, we have designed a novel halo painting network that learns to map approximate 3D dark matter fields to realistic halo distributions
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Mourier, Pierre. "Cosmologie inhomogène relativiste : modèles non perturbatifs et moyennes spatiales des équations d’Einstein." Thesis, Lyon, 2019. http://www.theses.fr/2019LYSE1116/document.
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Dans le modèle standard de la cosmologie, la dynamique globale de l'Univers est modélisée par l'intermédiaire d'un espace-temps de référence (ou de fond) fortement symétrique, admettant des sections spatiales homogènes et isotropes. Le couplage entre les sources fluides, homogènes, et l'expansion globale, y est déterminé par les équations d'Einstein de la Relativité Générale. La formation de structures inhomogènes de matière peut également être décrite dans ce modèle. Selon l'époque et l'échelle considérées, cette description est effectuée soit à l'aide d'un schéma perturbatif relativiste supposant une faible déviation de chaque grandeur par rapport au fond homogène imposé, soit au moyen d'une approche newtonienne au sein du même fond en expansion. L'interprétation des observations dans ce modèle suggère cependant une accélération inattendue de l'expansion, qui requiert une nouvelle composante énergétique mal comprise, l' «Énergie Noire», en plus de la Matière Noire. La cosmologie inhomogène a pour but de lever les restrictions imposées par ces modèles sur la géométrie et sur les sources sans sortir du cadre de la Relativité Générale. Cela peut notamment permettre d'améliorer le modèle de formation des structures pour prendre en compte de fortes déviations par rapport à l'homogénéité dans la distribution de matière et dans la géométrie. Cela permet également d'étudier les conséquences dynamiques, appelées effets de rétroaction («backreaction»), du développement local de telles inhomogénéités sur l'expansion à de plus grandes échelles. De telles rétroactions peuvent alors reproduire, au moins partiellement, les comportements attribués à l'Énergie Noire ou à la Matière Noire. Au cours de mon travail de thèse sous la direction de Thomas Buchert, j'ai étudié plusieurs aspects analytiques de la cosmologie inhomogène en Relativité Générale. Je présente ci-dessous les résultats de travaux au sein de collaborations, auxquels j'ai apporté des contributions majeures dans le cadre de la thèse. Je me suis tout d'abord concentré sur l'écriture d'un schéma d'approximation relativiste lagrangien, pour décrire la dynamique locale des structures jusqu'à un régime non-linéaire, dans des fluides parfaits barotropes irrotationnels. Je me suis ensuite intéressé à la description effective de fluides inhomogènes admettant un tenseur d'énergie-impulsion général ainsi que de la vorticité, au moyen de deux schémas possibles de moyenne spatiale. Ces schémas s'appliquent à un choix quelconque des hypersurfaces spatiales sur lesquelles moyenner, et fournissent pour chacun de ces choix un système d'équations d'évolution effectives, présentant plusieurs termes de rétroaction, pour un domaine d'intégration suivant la propagation des sources. Cela permet une discussion qualitative de la dépendance au choix du feuilletage des équations moyennes et des rétroactions. J'ai également étudié la réécriture de ces schémas de moyennes et équations d'évolution, et d'autres obtenus de façon similaire, sous une forme unifiée et manifestement 4-covariante. Ce dernier résultat permettra une étude plus explicite de la dépendance au feuilletageIn the standard model of cosmology, the global dynamics of the Universe is modelled via a highly symmetric background spacetime with homogeneous and isotropic spatial sections. The coupling of the homogeneous fluid sources to the overall expansion is then determined by the Einstein equations of General Relativity. In addition, the formation of inhomogeneous matter structures is described either via a relativistic perturbation scheme assuming small deviations of all fields to the prescribed homogeneous background, or using Newtonian dynamics within the same expanding background, depending on the scale and epoch. However, the interpretation of observations within this model calls for an unexpectedly accelerated expansion requiring a poorly-understood `Dark Energy' component, in addition to Dark Matter. Inhomogeneous cosmology aims at relaxing the restrictions of these models on the geometry and sources while staying within the framework of General Relativity. It can allow, in particular, for an improved modelling of the formation of structures accounting for strong deviations from homogeneity in the matter distribution and the geometry. It can also study the dynamical consequences, or backreaction effects, of the development of such inhomogeneities on the expansion of larger scales. Such a backreaction may then reproduce, at least partially, the behaviours attributed to Dark Energy or Dark Matter. During my PhD under the direction of Thomas Buchert, I have been working on several analytical aspects of general-relativistic inhomogeneous cosmology. I present below the results of collaborations in which I played a major role in the context of the PhD. I first focussed on the expression of a relativistic Lagrangian approximation scheme for the description of the local dynamics of structures up to a nonlinear regime in irrotational perfect barotropic fluids. I then considered the effective description of inhomogeneous fluids with vorticity and a general energy-momentum tensor in terms of two possible schemes of spatial averaging. These schemes are applicable to any choice of spatial hypersurfaces of averaging, providing for each choice a set of effective evolution equations, featuring several backreaction terms, for an averaging region comoving with the sources. This allows for a qualitative discussion of the dependence of the average equations and backreactions on the foliation choice. I also studied the rewriting of such averaging schemes and evolution equations under a unified and manifestly 4-covariant form. This latter result will allow for a more explicit investigation of foliation dependence
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Bel, Julien. "Les moments cumulant d'ordre supérieur à deux points des champs cosmologiques : propriétés théoriques et applications." Thesis, Aix-Marseille, 2012. http://www.theses.fr/2012AIXM4715/document.
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La philosophie de cette thèse est de dire que nos plus grandes chances de trouver et de caractériser les ingrédients essentiels du modèle cosmologique passe par l'élargissement de l'éventail des méthodes que l'on peut utiliser dans le but de trouver une nouvelle physique. Bien qu'il soit d'une importance primordiale de continuer à affiner, à de-biaiser et à rendre plus puissantes, les stratégies qui ont contribué à établir le modèle de concordance, il est également crucial de remettre en question, avec de nouvelles méthodes, tous les secteurs de l'actuel paradigme cosmologique. Cette thèse, par conséquent, s'engage dans le défi de développer des sondes cosmologiques nouvelle et performantes qui visent à optimiser les résultats scientifiques des futures grand sondages de galaxies. L'objectif est double. Du côté théorique, je cherche à mettre au point de nouvelles stratégies de test qui sont peu (voire pas du tout) affectées par des incertitudes astrophysiques ou par des modèles phénoménologiques qui ne sont pas complet . Cela rendra les interprétations cosmologiques plus facile et plus sûr. Du côté des observations, l'objectif est d'évaluer les performances des stratégies proposées en utilisant les données actuelles, dans le but de démontrer leur potentiel pour les futures grandes missions cosmologiques tels que BigBoss et EUCLIDThe philosophy of this thesis is that our best chances of finding and characterizing the essential ingredients of a well grounded cosmological model is by enlarging the arsenal of methods with which we can hunt for new physics. While it is of paramount importance to continue to refine, de-bias and power, the very same testing strategies that contributed to establish the concordance model, it is also crucial to challenge, with new methods, all the sectors of the current cosmological paradigm. This thesis, therefore, engages in the challenge of developing new and performant cosmic probes that aim at optimizing the scientific output of future large redshift surveys. The goal is twofold. From the theoretical side, I aim at developing new testing strategies that are minimally (if not at all) affected by astrophysical uncertainties or by not fully motivated phenomenological models. This will make cosmological interpretations easier and safer. From the observational side, the goal is to gauge the performances of the proposed strategies using current, state of the art, redshift data, and to demonstrate their potential for the future large cosmological missions such as BigBOSS and EUCLID
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Rosdahl, Karl Joakim. "Cosmological RHD simulations of early galaxy formation." Thesis, Lyon 1, 2012. http://www.theses.fr/2012LYO10075/document.
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Avec l’essor actuel de la sophistication et de l’efficacité des codes de cosmologie hydrodynamique,il est devenu possible d’inclure le transfert radiatif (RT) des photons ionisants dansles simulations cosmologiques, soit en post-traitement, soit en simulations couplées rayonnement+hydrodynamique (RHD). Malgré de nombreux obstacles, il y a eu cette derniéredécennie beaucoup de recherches menées sur les différentes stratégies et implémentations,dû au fait qu’un nombre de problèmes intéressants peuvent être désormais abordés par laRT et RHD, par exemple comment et quand l’Univers s’est réionisé, comment l’émissionradiative des étoiles et des noyaux actifs de galaxies se comportent pour réguler la formationdes structures à des échelles petites et grandes, et quelles prédictions et interprétationsnous pouvons faire des phénomènes observés, tels que la forêt Lyman-alpha et des sourcesdiffuses de rayonnement.Cela coïncide avec l’avènement du télescope spatial James Webb (JWST) et d’autresinstruments de pointe qui sont sur le point de nous donner un aperçu sans précédent sur lafin des âges sombres de l’Univers, quand le cosmos est passé d’un état froid et neutre à unétat chaud et ionisé, à la suite de l’apparition des sources radiatives.Notre préoccupation principale étant les rétroactions radiatives des premieres structures,nous avons mis en place une version RHD du code cosmologique Ramses, que nous appelonsRamsesRT, basée sur la méthode des moments. Ce code nous permet d’étudier les effets durayonnement ionisant dans les simulations cosmologiques RHD qui tirent pleinement profitdes stratégies de raffinement adaptif de grille et de parallélisation de Ramses. Pour rendreauto-cohérent le RHD nous avons également mis en oeuvre une thermochimie hors-équilibreincluant des espèces de l’Hydrogène et de l’Hélium qui interagissent avec le rayonnementtransporté.Je présente dans cette thèse une description détaillée de RamsesRT et de nombreux testscontribuant à sa validation.Jusqu’à présent nous avons utilisé RamsesRT pour étudier l’émission Lyman-alpha decourants d’accrétion, qui sont prédits à grand redshift par les simulations cosmologiques,mais n’ont jamais été clairement identifiés par les observations. Nous avons également étudiéle chauffage gravitationnel dans ces courants pour déterminer si ce dernier pouvait être lasource motrice principale des Lyman-alpha blobs, un phénomène observé qui a été beaucoupétudié et débattu au cours de la dernière décennie. Cet étudie nous permet de conclure queles Lyman-alpha blobs peuvent, en principe, être alimentés par le chauffage gravitationnel,et que d’autre part, les courants d’accrétion sont sur le point d’être directement détectablesavec des instruments à venir.Mes intentions futures sont d’utiliser RamsesRT dans les simulations cosmologiques àhaute résolution, de la formation des premiéres galaxies jusqu’à l’époque de la réionisation,et ainsi étudier comment la rétroaction radiative affecte la formation et l’évolution de cesgalaxies et de faire des prévisions d’observation qui peuvent être testées avec des instrumentssophistiqués tels que le JWSTWith the increasing sophistication and efficiency of cosmological hydrodynamics codes, ithas become viable to include ionizing radiative transfer (RT) in cosmological simulations,either in post-processing or in full-blown radiation-hydrodynamics (RHD) simulations. Inspite of the many hurdles involved, there has been much activity during the last decade or soon different strategies and implementations, because a number of interesting problems canbe addressed with RT and RHD, e.g. how and when the Universe became reionized, howradiation from stars and active galactic nuclei plays a part in regulating structure formationon small and large scales, and what predictions and interpretations we can make of observedphenomena such as the Lyman-alpha forest and diffuse sources of radiation.This coincides with the advent of the James Webb space telescope (JWST) and otherstate-of-the-art instruments which are about to give us an unprecedented glimpse into theend of the dark ages of the Universe, when the cosmos switched from a cold and neutralstate to a hot and ionized one, due to the turn-on of ionizing radiative sources.With a primary interest in the problem of radiative feedback in early structure formation,we have implemented an RHD version of the Ramses cosmological code we call RamsesRT,which is moment based and employs the local M1 Eddington tensor closure. This code allowsus to study the effects of ionizing radiation on-the-fly in cosmological RHD simulationsthat take full advantage of the adaptive mesh refinement and parallelization strategies ofRamses. For self-consistent RHD we have also implemented a non-equilibrium chemistry ofthe atomic hydrogen and helium species that interact with the transported radiation.I present in this thesis an extensive description of the RamsesRT implementation andnumerous tests to validate it.Thus far we have used the RHD implementation to study extended line emission fromaccretion streams, which are routinely predicted to exist at early redshift by cosmologicalsimulations but have never been unambiguously verified by observations, and to investigatewhether gravitational heating in those streams could be the dominant power source ofso-called Lyman-alpha blobs, an observed phenomenon which has been much studied anddebated during the last decade or two. Our conclusions from this investigation are thatLyman-alpha blobs can in principle be powered by gravitational heating, and furthermorethat accretion streams are on the verge of being directly detectable for the first time withupcoming instruments.My future intent is to use RamsesRT for high-resolution cosmological zoom simulations ofearly galaxy formation, up to the epoch of reionization, to study how radiative feedbackaffects the formation and evolution of those galaxies and to make observational predictionsthat can be tested with upcoming instruments such as the JWST
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Wallisch, Benjamin. "Cosmological probes of light relics." Thesis, University of Cambridge, 2018. https://www.repository.cam.ac.uk/handle/1810/283003.
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One of the primary targets of current and especially future cosmological observations are light thermal relics of the hot big bang. Within the Standard Model of particle physics, an important thermal relic are cosmic neutrinos, while many interesting extensions of the Standard Model predict new light particles which are even more weakly coupled to ordinary matter and therefore hard to detect in terrestrial experiments. On the other hand, these elusive particles may be produced efficiently in the early universe and their gravitational influence could be detectable in cosmological observables. In this thesis, we describe how measurements of the cosmic microwave background (CMB) and the large-scale structure (LSS) of the universe can shed new light on the properties of neutrinos and on the possible existence of other light relics. These cosmological observations are remarkably sensitive to the amount of radiation in the early universe, partly because free-streaming species such as neutrinos imprint a small phase shift in the baryon acoustic oscillations (BAO) which we study in detail in the CMB and LSS power spectra. Building on this analytic understanding, we provide further evidence for the cosmic neutrino background by independently confirming its free-streaming nature in different, currently available datasets. In particular, we propose and establish a new analysis of the BAO spectrum beyond its use as a standard ruler, resulting in the first measurement of this imprint of neutrinos in the clustering of galaxies. Future cosmological surveys, such as the next generation of CMB experiments (CMB-S4), have the potential to measure the energy density of relativistic species at the sub-percent level and will therefore be capable of probing physics beyond the Standard Model. We demonstrate how this improvement in sensitivity can indeed be achieved and present an observational target which would allow the detection of any extra light particle that has ever been in thermal equilibrium. Interestingly, even the absence of a detection would result in new insights by providing constraints on the couplings to the Standard Model. As an example, we show that existing bounds on additional scalar particles, such as axions, may be surpassed by orders of magnitude.
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Santiago, Bautista Iris del Carmen. "Étude des propriétés des galaxies dans les structures filamentaires." Thesis, Toulouse 3, 2020. http://www.theses.fr/2020TOU30034.
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La composante baryonique de la structure à grande échelle de l’Univers est composée de concentration de gaz et de galaxies, donnant lieu à des groupes, à des amas, à des filaments allongés et à des murs étendus. Ces structures peuvent suivre la distribution de matière noire dans l’Univers. Néanmoins, selon le modèle cosmologique actuel, l’ensemble des matières baryoniques dans l’Univers n’a pas encore été observé. Cependant, les simulations numériques nous suggèrent qu’entre la moitié et deux tiers des parties des baryons sont localisées entre les amas de galaxies et peuplent les structures qui les relient. Les structures les plus concentrées, que nous appelons ici « des systèmes » (i.e. groupes et amas), ont généralement des gaz à haute concentration et une température élevée (1 - 10 keV). Cette température se refroidit en émettant des photons qui sont observables en rayons X. De plus les gaz interagissent avec les photons du fond diffuse cosmologique par l’effet Sunyaev–Zel'dovich (SZ) , observable à longueur d’onde millimétrique. Dans les filamentaires et murs qui sont des structures moins denses, les baryons sont probablement dans un état moins dense et à une température modérée (0.01 - 1 keV). Ces gaz tièdes sont appelés WHIM (Warm Hot Intergalactic Medium). Pendant cette Thèse de doctorat nous étudions les effets environnementaux associés aux différents composants de la structure à grande échelle de l’Univers. Pour les systèmes, l'objectif est la caractérisation du milieu intra amas en utilisant l’effet SZ. Pour cela nous utilisons les observations du satellite Planck et de l’Atacama Cosmological Télescope (ACT) afin d’analyser les profils de pression pour un échantillon d’amas de faible masse. D'autre part, pour l'étude des structures à faible densité (structures filamentaires). Nous avons construit un échantillon de candidats à filaments, cet échantillon se compose des chaînes d’amas reliées en une structure de super amas de galaxies. Notre objectif est de prouver leur nature filamentaire et de caractériser ses composants (galaxies, amas et gaz)The baryonic component of the Large Scale Structure (LSS) of the Universe is composed by concentrations of gas and galaxies forming groups, clusters, elongated filaments and widely spread sheets which probably underline the distribution of dark matter. Nevertheless, according to the current cosmological models, most of the baryonic material in the Universe has not yet been directly observed. Numerical simulations suggest that from one-half to two-thirds of all baryons may be located out of clusters of galaxies, pervading the structures between them. The most concentrated structures, which we call systems of galaxies (i.e., groups and clusters) usually contain high density hot gas (1 - 10 keV) that cools radiatively, emits at X-rays wavelengths and interacts with the cosmic microwave background at millimeter wavelengths (Sunyaev Zel'dovich effect, SZ). For the less dense structures, filaments and sheets, the baryons are probably in moderately hot gas phase (0.01 - 1 keV), commonly named as warm hot intergalactic medium (WHIM). In this PhD Thesis, we study the environmental effects associated to the different components of the LSS. For the galaxy systems, we aim to characterize the intra cluster medium (ICM) through the analysis of the S-Z effect. We employ the ACT and Planck data to analyze the gas pressure profiles of a sample of low mass galaxy clusters. For the least dense structures, we assembled a sample of filament candidates composed by chains of clusters that are located inside superclusters of galaxies. We aim to probe the filament structure skeletons and characterize their components (galaxies, groups/clusters and gas)
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Whitbourn, Joseph. "Exploring cosmology via large scale structure." Thesis, Durham University, 2013. http://etheses.dur.ac.uk/9459/.
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This thesis presents a study of the large-scale structure (LSS) of the Universe as evidenced in observations of the cosmic microwave background (CMB) and in galaxy redshift surveys. We first investigate several anomalies reported in the Wilkinson Microwave Anisotropy Probe (WMAP) CMB temperature map. In particular, we have used the Planck Early Data Release to test the WMAP beam profiles. We confirm that stacked beam profiles at Q, V and particularly at W, appear wider than expected when compared to the Jupiter beam, normalised either directly to the radio source profiles or using Planck fluxes. We also find that the WMAP source fluxes demonstrate possible non-linearity with Planck fluxes. Additionally, we find that the stacked Sunyaev-Zel'dovich (SZ) decrements of galaxy clusters observed by Planck are in agreement with the WMAP data. We find that there is no evidence for a WMAP SZ deficit as has previously been reported. We conclude that beam profile systematics can have significant effects on the CMB power spectrum with potentially important implications for Cosmology parameter fitting. We have also mapped the local density field using K and r limited galaxy redshift distributions and number counts from the 6dF Galaxy Redshift Survey (6dFGS), Two Micron All Sky Survey (2MASS), Galaxy And Mass Assembly (GAMA) and Sloan Digital Sky Survey (SDSS) redshift surveys. We find evidence for significant galaxy underdensities in three large regions of the high latitude sky. This is in agreement with the corresponding peculiar velocities which are not compatible with recovering the CMB rest frame in the volume probed. We therefore conclude that there is some consistent evidence from both counts and Hubble diagrams for a `Local Hole' with a ≈ 150h−1Mpc under-density that deeper counts and redshifts in the Northern Galactic cap suggest may extend to ≈ 300h−1 Mpc.
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Ma, Yin-Zhe. "Cosmology with CMB and large scale structure." Thesis, University of Cambridge, 2011. https://www.repository.cam.ac.uk/handle/1810/239394.
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Cosmology has become a precision science due to a wealth of new precise data from various astronomical observations. It is therefore important, from a methodological point of view, to develop new statistical and numerical tools to study the Cosmic Microwave Background (CMB) radiation and Large Scale Structure (LSS), in order to test different models of the Universe. This is the main aim of this thesis. The standard inflationary -dominated Cold Dark Matter ( CDM) model is based on the premise that the Universe is statistically isotropic and homogeneous. This premise needs to be rigorously tested observationally. We study the angular correlation function C(θ) of the CMB sky using the WMAP 5-year data, and find that the low-multipoles can be reconstructed from the data outside the sky cut. We apply a Bayesian analysis and find that S1/2 statistic (S1/2 = R [C(θ)]2d cos θ, used by various investigators as a measure of correlations at large angular scales) cannot exclude the predictions of the CDM model. We clarify some issues concerning estimation of correlations on large angular scales and their interpretation. To test for deviation from statistical isotropy, we develop a quadratic maximum likelihood estimator which we apply to simulated Planck maps. We show that the temperature maps from Planck mission should be able to constrain the amplitude of any spherical multipole of a scaleinvariant quadrupole asymmetry at the 1% level (2σ). In addition, polarization maps are also precise enough to provide complimentary constraints. We also develop a method to search for the direction of asymmetry, if any, in Planck maps. B-mode polarisation of the CMB provides another important test of models of the early Universe. Different classes of models, such as single-field inflation, loop quantum cosmology and cosmic strings give speculative but testable predictions. We find that the current ground-based experiments such as BICEP, already provided fairly tight constraints on these models. We investigate how these constraints might be improved with future observations (e.g. Planck, Spider). In addition to the CMB related research, this thesis investigates how peculiar velocity fields can be used to constrain theoretical models of LSS. It has been argued that there are large bulk flows on scales of & 50 Mpc/h. If true, these results are in tension with the predictions of the CDM model. We investigate a possible explanation for this result: the unsubtracted intrinsic dipole on the CMB sky may source this apparent flow, leading to the illusion of the tilted Universe. Under the assumption of a superhorizon isocurvature fluctuation, the constraints on the tilted velocity require that inflation lasts at least 6 e-folds longer (at the 95% confidence interval) than that required to solve the horizon problem. Finally, we investigate Cosmic Mach Number (CMN), which quantifies the ratio between the mean velocity and the velocity dispersion of galaxies. We find that CMN is highly sensitive to the growth of structure on scales (10, 150) Mpc/h, and can therefore be used to test modified gravity models and neutrino masses. With future CMN data, it should be possible to constrain the growth factor of linear perturbation, as well as the sum of the neutrino mass to high accuracy.
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Sutherland, William James. "Large-scale structure in the universe." Thesis, University of Cambridge, 1989. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.317881.
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Fantaye, Yabebal. "Probing primordial non-Gaussianity using large scale structure." Master's thesis, University of Cape Town, 2009. http://hdl.handle.net/11427/6101.
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Includes abstract.Includes bbliographical references (leaves 65-69).
Recent evidence from the WMAP satellite has lead to a tentative detection of non-Gaussianity. Using the bispectrum statistic applied to the MegaZ catalogue of over 600,000 luminous red galaxies we find new bounds on the large-scale nonGaussianity. We constrain the fNL parameter using a particular type of triangular configuration as well as the combination of all the possible triangles in harmonic space. The constraint on fNL from the combination of all possible triangular configurations is ffV'ial = 57 ± 52 with 68% confidence limit, which is consistent with vanishing primordial non-Gaussianity, although some triangular configurations on their own suggest a non-zero bispectrum which, if confirmed, would have a profound effect on modern cosmology.
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Pediani, Steven. "Dark energy and large scale structure." Thesis, University of Manchester, 2011. https://www.research.manchester.ac.uk/portal/en/theses/dark-energy-and-large-scale-structure(44224ea0-265c-4d78-931a-298d79d3ab9d).html.
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Currently one of the most exciting problems in cosmology is the nature of dark energy, which is responsible for the late time accelerated expansion of the universe. Dark energy modifies the distance-redshift relation, and governs the late time evolution of gravitational potentials in the universe. Therefore by observing large scale structure we can gain valuable information on the nature of dark energy. In this thesis we examine a particular theory of dark energy, known as elastic dark energy. Using weak lensing and the ISW effect, coupled with CMB and SNIa data, we find lower bounds for the sound speed of elastic dark energy. We also explore how this model behaves in the presence of collapsing matter.
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Kopp, Michael. "Models of large scale structure formation in cosmology." Diss., Ludwig-Maximilians-Universität München, 2014. http://nbn-resolving.de/urn:nbn:de:bvb:19-172479.
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Combining all knowledge we have gathered about the origin, evolution and current state of the universe it appears indisputable that 95% of the mass-energy density in today's universe is comprised of unknown substances called dark matter and dark energy. This thesis explores different aspects of and develops models for the formation of the largest structures we observe in the universe, because these structures -- the cosmic web made of dark matter halos, clusters of galaxies and galaxies -- sensitively depend on properties of dark matter and dark energy, in particular on their abundances, the equation of state of and possible new interactions mediated by dark energy.
Current and upcoming surveys map the large scale structure (LSS) with increasingly higher precision and in larger volumes. In order to optimally extract cosmological parameters we need to build accurate models for LSS formation that also describe how LSS is perceived by real observers trough processes affecting light propagation. Only then can we reliably reconstruct the cosmological parameters and identify the models for dark matter and dark energy preferred by the data. Therefore this thesis contributes to the endeavor to ultimately uncover the nature of dark matter and dark energy.
Chapter 2 studies a dark energy model which mediates a ``fifth force'' enhancing Newtonian gravity only on large scales due to the chameleon mechanism, but leads to an expansion history indistinguishable from the case where dark energy is a cosmological constant. Hence the only observables that can discriminate them are related to structure formation. We study the abundance of dark matter halos per halo mass with semi-analytical techniques to find a fit function depending on the model parameter responsible for the range and strength of the fifth force. We find good agreement with Monte-Carlo and N-body simulations of the mass function. Our result is a fit function for the halo mass function that can be used to constrain this model and to look for signatures of the chameleon effect in observations of galaxy of clusters.
In Chapters 3 and 4 we show why it is justified to use Newtonian gravity instead of General Relativity on all scales to accurately describe LSS formation in a universe governed by a cosmological constant and cold dark matter.
In Chapter 5 we show that a complex scalar field solving the Schrödinger-Poisson equation is able describe collisionless selfgravitating dark matter with the same number of degrees of freedom as the popular dust fluid. In contrast to the dust model it does not suffer from singularities and thus allows the analytical and numerical study of fully nonlinear effects like halo formation.
In Chapter 6 we study the clustering of halos as observed in redshift space, by developing an improved model for the halo dynamics based on a coarse grained dust model and by extending the so called Gaussian streaming model to general phase space distribution functions. We compare our results to a N-body simulation halo catalog and find that the coarse grained dust model significantly improves the accuracy of theoretical redshift space correlation functions.Wenn wir all das Wissen kombinieren, welches wir bisher über Ursprung, Entwicklung und heutigen Zustand des Universum gesammelt haben, kommen wir unweigerlich zu dem Schluss, dass 95% der Materiedichte des Universums aus unbekannten Substanzen besteht, die man dunkle Materie und dunkle Energie nennt. Diese Dissertation beschäftigt sich mit verschiedenen Aspekten der Entstehung der größten Strukturen im Universum und entwickelt neue Methoden diese Strukturen, bestehend aus dem kosmischen Netz, Galaxienhaufen und Galaxien zu modellieren. Diese Strukturen hängen sehr sensibel von den Eigenschaften der dunklen Materie und dunklen Energie ab, insbesondere von ihren relativen und absoluten Mengen, sowie der Zustandsgleichung der dunklen Energie und einer eventuell von ihr vermittelten neuen Wechselwirkung. Aktuell durchgeführte und zukünftige Vermessungen der größten Strukturen kartographieren diese mit zunehmender Präzision und in immer größeren Volumen. Um die kosmologischen Parameter bestmöglich aus den Daten zu extrahieren, benötigen wir akkurate Modelle der Strukturbildung und der Prozesse, die das Licht auf seinem Weg zum Beobachter beeinflussen. Nur so können wir zuverlässig die kosmologischen Parameter rekonstruieren und die Modelle für dunkle Materie und dunkle Energie identifizieren die von den Daten bevorzugt werden. Somit trägt die Dissertation zu den Bemühungen bei, die Natur der dunklen Materie und dunklen Energie zu enthüllen. Kapitel 2 untersucht ein Modell für dunkle Energie, welche eine ``fünfte Kraft'' vermittelt, die jedoch die Newtonsche Gravitationskraft auf Grund des Chamäleon-Mechanismus lediglich auf großen Skalen verstärkt und eine Expansionsgeschichte verursacht, die nicht vom einfachsten Fall zu unterscheiden ist, bei dem die dunkle Energie eine kosmologische Konstante ist. Deswegen stehen die einzigen Beobachtungsgrößen, welche die Modelle zu unterscheiden vermögen im Zusammenhang mit Strukturbildung. Wir untersuchen mit semi-analytischen Methoden die Häufigkeit von dunkle-Materie-Halos pro Halo-Masse und erhalten für diese eine Fitfunktion, die vom Wert des neuen Modellparameters abhängt, welcher die Reichweite und Stärke der fünften Kraft bestimmt. Wir finden eine gute übereinstimmung der auf diese Weise bestimmten theoretischen Massenfunktion mit denjenigen bestimmt aus Monte-Carlo und N-Teilchen Simulationen. Die von uns gefundene Fitfunktion vermag das Modell durch Beobachtungen von Galaxienhaufen zu testen und kann dazu dienen nach den charakteristischen Signaturen des Chamäleon-Mechanismus in den Beobachtungsdaten zu suchen. In Kapitel 3 und 4 zeigen wir, dass die Newtonsche Gravitationstheorie anstelle der Allgemeinen Relativitätstheorie auf allen Längenskalen verwendet werden kann, um akkurat die Entstehung der größten Strukturen zu beschreiben, sofern das Universum von kalter dunkler Materie und einer kosmologischen Konstante dominiert wird. In Kapitel 5 zeigen wir, dass ein komplexes Skalarfeld, welches die Schrödinger-Poisson-Gleichung erfüllt, in der Lage ist kollisionsfreie selbstgravitierende dunkle Materie mit der selben Zahl an Freiheitsgraden zu beschreiben wie das weitverbreitete Staubmodell. Im Gegensatz zum Staubmodell ist das Skalarfeldmodell frei von Singularitäten, weswegen es analytische und numerische Studien von komplett nichtlinearen Prozessen wie Halo-Entstehung erlaubt. In Kapitel 6 untersuchen wir die Clusterung von Halos, oder die Halo-Korrelationsfunktion, wie sie im Rotverschiebungsraum beobachtet wird. Dazu entwickeln wir ein verbessertes Modell für die Dynamik von Halos, welches auf einer Körnung des Staubmodells und einer Verallgemeinerung des Gaussian-Streaming-Modells auf beliebige Phasenraumfunktionen beruht. Wir vergleichen unsere Resultate mit Messgrößen aus einer N-Teilchen-Simulation und finden, dass das granulierte Modell die Genauigkeit der vorhergesagten Korrelationsfunkionen im Rotverschiebungsraum wesentlich verbessert.
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Sagredo, Briones Bryan Lester. "Bayesian statistical methods on large scale structure cosmology." Tesis, Universidad de Chile, 2018. http://repositorio.uchile.cl/handle/2250/168494.
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Tesis para optar al grado de Magíster en Ciencias, Mención FísicaEn esta tesis se introduce el formalismo de la estadística Bayesiana aplicado a cosmología LCDM y otros modelos de energía oscura, enfocado en los observables de agrupamiento de galaxias y de crecimiento cósmico. Se explora un gran rango de aplicaciones del marco de trabajo Bayesiano. Primero, se exploran las posibilidades de predicción de la estadística Bayesiana con nuestro primer proyecto, el cual consiste en la aplicación del método de Aproximación de Verosimilitudes con Derivadas (DALI por sus siglas en inglés) para mejorar las predicciones de Matriz de Fisher de un experimento de agrupamiento de galaxias tipo LSST. El método contiene una expansión de Taylor hasta el tercer orden a partir del punto de parámetros de confianza, capturando formas de las regiones de confianza que van más allá de las usuales elipses de Fisher en la bibliografía. Además se compara con muestras de Cadenas de Markov Monte Carlo para mostrar la efectividad del método. Luego, realizamos un proyecto acerca de la aplicación del formalismo de la Robustez Interna a una compilación de datos de crecimiento cósmico, el cual es un método Bayesiano que potencialmente puede detectar outliers (datos aislados), errores sistemáticos o nuevas leyes físicas en los datos, considerando la posibilidad de que subconjuntos de los datos sigan diferentes parámetros o modelos (incluyendo de esta manera el aspecto de comparación de modelos básico de la estadística Bayesiana). No se encuentran errores sistemáticos ni outliers en el set de datos, así asegurando su robustez interna. Finalmente, tomamos por completo el campo de comparación de modelos Bayasiana, y lo hacemos via un estudio acerca de diferentes métodos de comparación de modelos cosmológicos. Se comparan varios modelos de energía oscura usando datos crecimiento cósmico y expansión cósmica, y esto se hace utilizando cuatro criterios de comparación: Comparación de evidencias, Criterio de Información Bayesiano, Criterio de Información de Akaike y un método reciente de Figura de Mérito. Luego, se discute acerca de la efectividad y conveniencia de cada uno de ellos.
CONICYT Powered@NLHPC: Esta tesis fue parcialmente apoyada por la intraestructura de supercómputo del NLHPC (ECM-02)
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Durrive, Jean-Baptiste. "Baryonic processes in the large scale structuring of the Universe." Thesis, Université Paris-Saclay (ComUE), 2016. http://www.theses.fr/2016SACLS346/document.
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Ma thèse porte sur deux questions importantes de la Cosmologie:(i) L'origine des champs magnétiques cosmologiques:L'Univers semble magnétisé à absolument toutes ses échelles (spatiales et temporelles), y compris le milieu intergalactique. Mais leur origine est encore inconnue à l'heure actuelle, malgré les nombreux efforts pour essayer de répondre à cette question. On pense qu'ils ont d'abord été générés avec de très faibles amplitudes, puis qu'ils ont été amplifiés au cours de la formation des structures. La turbulence dans les galaxies et les amas de galaxies modifie totalement l'organisation initiale de ces champs, ce qui fait que les champs observés actuellement dans les structures ne nous renseignent pas sur leur origine. Il convient donc de s'intéresser aux champs intergalactiques. J'ai dévelopé analytiquement un modèle de magnétogénèse basé sur la photoionisation du milieu intergalactique par les premières étoiles et les premières galaxies apparues dans l'Univers, il y a environ 13 milliards d'années. Puis, en collaboration avec H. Tashiro et N. Sugiyama (Japon), j'ai calculé de façon analytique la densité d'énergie moyenne injectée par ce processus dans le contexte cosmologique, et en parallèle, en collaboration avec D.Aubert (France), j'ai étudié les propriétés statistiques du champs généré à travers des simulations numériques. Nos prédictions sont compatibles avec les observations actuelles. Ce mécanisme a donc dû participer à la magnétisation de l'Univers à ses plus grandes échelles.(ii) Fragmentation gravitationnelle de la toile cosmique:Les simulations numériques suggèrent que la matière dans l'Univers est répartie de façon filamentaire, les noeuds de ce réseau étant les amas de galaxies. La matière s'écoule le long de ces filaments. L'accrétion dans les noeuds est donc anisotrope, et il s'avère qu'elle est aussi en partie intermittente. Cela indique que la matière ne se structure pas uniquement dans les amas, mais aussi dans les filaments, voire les nappes ou les vides cosmiques. Je me suis donc intéressé à l'instabilité gravitationnelle dans les milieux stratifiés. J'ai proposé une nouvelle approche, dans le cadre de la théorie spectrale, en m'inspirant de la littérature plasmaMy thesis deals with two important topics of Cosmology:(i) Origin of cosmological magnetic fields:Magnetic fields seem ubiquitous in the Universe, present at all scales and all times, probably even in the entire intergalactic medium. Their origin is still unclear, especially on the largest scales. The current paradigm is that they were first generated with extremely weak strengths, and later amplified during structure formation. Because of turbulence, the fields we observe in galaxies and galaxy clusters lost their initial characteristics. However, in less dense regions such as cosmological filaments, sheets or voids, magnetic fields have evolved more mildly. Therefore, intergalactic magnetic fields may still possess a memory of the processes that generated them and hold the key to their origin. I developed analytically a detailed physical model of a natural astrophysical mechanism that generates intergalactic magnetic fields during the first billion year, namely at the time when first stars and galaxies were born. Then, in collaboration with H. Tashiro and N. Sugiyama (Japan), I computed analytically the mean energy density injected in the entire Universe through this mechanism. Independently, in collaboration with D. Aubert (France), I derived the topological and statistical properties of the magnetic field thus generated, using cosmological numerical simulations. This way I demonstrated that this simple, natural photoionization-based magnetogenesis must have created magnetic seed fields with properties a priori perfectly compatible with present day observations.(ii) Gravitational fragmentation of the cosmic web:Cosmological numerical simulations suggest that the Universe has a web-like structure, the nodes of which are galaxy clusters. These nodes are supplied with matter flowing along the filaments interconnecting them. Part of this accretion occurs intermittently, which indicates that clumps of matter form not only inside clusters themselves, but also either in cosmic voids, walls and/or filaments. I studied gravitational instability in stratified media in the frame of spectral theory, in planar and cylindrical geometries, relevant for cosmic walls and filaments, for isothermal, polytropic, and with and without an external gravitational background (e.g. Dark Matter). I have recasted the problem as an eigenvalue problem in the force operator formalism, and derived the wave equation governing the growth of perturbations. I also studied it in matrix form, which gives complementary information
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Graham, Matthew James. "Large-scale structure of the early universe." Thesis, University of Central Lancashire, 1997. http://clok.uclan.ac.uk/21834/.
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The large-scale structure of the universe is one of the most active areas of research in modern astronomy. However, until recently our knowledge of the distribution of matter on large scales has been primarily limited to two epochs - the present epoch and the epoch of recombination - and consequently it has proved difficult to distinguish between competing models of structure formation and evolution. Quasars are an ideal tracer of the matter distribution on large scales at different periods in the evolution of the universe and can therefore tell us much about the large-scale structure of the early universe. The main subject of this thesis is an investigation into the nature and implications of coherent structures in the spatial distribution of quasars on scales of 100h 1 Mpc known as quasar groups. The first part of the thesis deals with the overall status of large-scale structure in the universe. After a review of our current knowledge of this subject, I present a new graph-theoretical method for finding large-scale structures in cosmological data sets, based on the minimal spanning tree (MST). The next part of the thesis focuses on observations of the largest quasar group known (Clowes & Campusano 1991a). I describe the observation, reduction and analysis of quasars, selected by the Automated Quasar Detection (AQD) software of Clowes (1986), as part of quasar surveys of two fields containing the quasar group. I also detail the preparation of a new wide-field survey for quasars, using selection by ultraviolet excess, centred on the quasar group. The results of the photometry used are presented in an appendix at the end of the thesis. The third part of the thesis considers the nature and theoretical implications of quasar groups. Using the results of the surveys described in the thesis, I present an analysis of the Clowes & Campusano group. I also calculate the expected density contrast on the scales of the three known quasar groups for a variety of cosmological models and compare these with the observed values. The final part of the thesis deals with the results of other quasar surveys on which I have participated. The main results of the thesis are: • the detection of two new candidates for large-scale structure in quasar surveys: a group of ten quasars at z ' 1.9, with dimensions of "- 120 x 90 x 20h3 Mpc 3 , and a grouping of seven Seyfert galaxies at z 0.19, with dimensions of 60 X 30 X lOh' 3 Mpc3; • the members of quasar groups show no peculiar characteristics compared with a general population of quasars; • assuming that quasar groups are equivalent to present-day superciusters, they are compatible with CDM and MDM models with o = 1 and H0 75 km s1 Mpc' and also with models involving late-time phase transitions. They are, however, incompatible at > 10o with models involving a non-zero cosmological constant, fo = 0.2 and models involving cosmic strings. • the discovery of a quasar with ultrastrong ultraviolet Fe II emission The unusual emission features seen in this quasar are explained by Lya fluorescence contributing significantly to the formation of Fe II emission.
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Picard, Alain Mould Jeremy. "The large scale structure of the universe /." Diss., Pasadena, Calif. : California Institute of Technology, 1991. http://resolver.caltech.edu/CaltechETD:etd-09172008-084234.
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Alimi, Jean-Michel. "Contributions : instabilite gravitationnelle dans un univers en expansion et formation des grandes structures, effets ponderomoteurs dans les plasmas magnetises." Paris 6, 1987. http://www.theses.fr/1987PA066234.
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Analyse de la fonction de correlation spatiale des galaxies, obtenue a partir de catalogues de galaxies, selon differentes procedures. La distribution des galaxies isolees dans le catalogue cfa est etudiee. Etude du collapse gravitationnel non lineaire de particules sans collision, du point de vue analytique et numerique. On montre l'importance du traitement tridimensionnel de ces processus gravitationnels et quelles peuvent en etre les consequences sur la formation des galaxies