1 |
QSO Pairs and the Lyman-alpha Forest: Observations, Simulations, and Cosmological ImplicationsMarble, Andrew R January 2007 (has links)
This dissertation addresses two cosmological applications of the Lyman-alpha (Ly ɑ) forest observed in QSO pairs separated by several arcminutes or less. The Ly ɑ flux autocorrelation and cross-correlation provide a measurement of cosmic geometry at z > 2, via a variant of the Alcock-Paczyński test. I present the results of an observing campaign to obtain moderate resolution spectroscopy of the Ly ɑ forest in QSO pairs with small redshift differences (Δz < 0.25) and arcminute separations (θ < 5'). This new sample includes 29 pairs and one triplet suitable for measuring the cross-correlation and 78 individual QSO spectra for determining the autocorrelation. Continuum fits are provided, as are seven revisions for previously published QSO identifications and/or redshifts. Using a suite of hydrodynamic simulations, anisotropies in the Ly ɑ flux correlation function due to redshift-space distortions and spectral smoothing are investigated for 1:8 ≤ z ≤ 3, further enabling future applications of the Alcock-Paczyński test with Ly ɑ correlation measurements. Sources of systematic error including limitations in mass-resolution and simulation volume, prescriptions for galactic outflow, and the observationally uncertain mean flux decrement are considered. The latter is found to be dominant. An approximate solution for obtaining the zero-lag cross-correlation for arbitrary spectral resolution is presented, as is a method for implementing the resulting anisotropy corrections while mitigating systematic uncertainty.
|
2 |
Cosmology with cosmic voids / La cosmologie avec les vides cosmiquesPisani, Alice 22 September 2014 (has links)
Les missions modernes permettent d’accéder à des mesures de qualité pour les grandes structures, en échantillonnant la distribution de galaxies en détail jusque dans les régions les moins denses, les vides. Toutefois, nous observons les vides dans l’espace des redshift, ce qui limite notre connaissance de ces structures. Afin d’utiliser les vides en tant qu’outils cosmologiques de précision, il est fondamental d’obtenir leur forme dans l’espace réel. Dans cette thèse nous présentons un algorithme non-paramétrique permettant de reconstruire les profils de densité sphérique des vides empilés dans l’espace réel, sans assomption pour les distorsions en redshift. Nous obtenons donc les premiers profils de densité des vides empilés dans l’espace réel, à travers lesquels nous étudions la compensation de masse et calculons les profils de vitesses particulières des vides, se basant sur la théorie linéaire et le modèle cosmologique. Nous discutons l’utilisation des profils pour contraindre indépendamment les vitesses. Avec des catalogues simulés de galaxies, nous analysons l’effet des vitesses particulières sur les propriétés physiques des vides. Enfin nous calculons une prédiction du nombre de vides que fournira la future mission Euclid et des contraintes que ce nombre de vides donnera sur les paramètres cosmologiques (grâce au formalisme de Fisher). Les profils de densité de vides dans l’espace réel peuvent être utilisés pour tester les modèles cosmologiques (à travers l’étude de l’effet des vitesses particulières et l’amélioration du test de Alcock-Paczynski); l’étude des vides promet donc d’apporter des informations indépendantes pour éclaircir le mystère de l’énergie obscure. / Modern surveys allow us to access to high quality measurements, by sampling the galaxy distribution in detail also in the emptier regions, voids. When we observe cosmic voids, however, we observe them in redshift-space: their real shape remains inaccessible to us, thus limiting our knowledge about such structures. To employ voids as a precision tool for Cosmology, it is fundamental to obtain their real-space shape. This thesis presents a model-independent non-parametric algorithm to reconstruct the spherical density profiles of stacked voids in real space, without assumptions about redshift distortions. With this algorithm, we obtain the first ever real-space density profiles of stacked voids. With the profiles we study the mass compensation and obtain a theoretical prediction for the velocity profiles of voids based on linear theory and assuming cosmological parameters. In parallel, we discuss the use of the real-space profiles to obtain model-independent information about the peculiar velocity profiles of voids. Also, using mock catalogues, we analyse the effect of peculiar velocities on void properties and discuss it in the framework of current and future surveys. Finally we calculate a forecast for void abundances with the future Euclid mission and obtain, using the Fisher matrix formalism, a prediction for the constraints that void abundances will set on cosmological parameters. The real-space profiles of voids can be used to test cosmological models (through the understanding of peculiar velocities effects and the improvement of the Alcock-Paczynski test); and void abundances promise to bring independent information and to shed light on the mystery of dark energy.
|
Page generated in 0.0201 seconds