Philosophiae Doctor - PhD / We investigate the clustering of HI-selected galaxies in the ALFALFA survey and compare results with those obtained for HIPASS. Measurements of the angular correlation function and the inferred 3D-clustering are compared with results from direct spatial-correlation measurements. We are able to measure clustering on smaller angular scales and for galaxies with lower HI masses than was previously possible. We calculate the expected clustering of dark matter using the redshift distributions of HIPASS and ALFALFA and show that the ALFALFA sample is somewhat more anti-biased with respect to dark matter than the HIPASS sample. We are able to conform the validity of the dark matter correlation predictions by performing simulations of the non-linear structure formation. Further we examine how the bias evolves with redshift for radio galaxies detected in the the first survey. / South Africa

The recent boom in 21cm astronomy has piqued the interest of many, especially cosmologists realizing its applications in their field. This study aims to determine if 21cm astronomy is a good tool for testing the validity of keV WDM models, as well as creating a code capable of simulating keV WDM models from an existing CDM code. The assumed WDM models vary only in dark matter particle mass and assume a single-species dark matter case as well as totally thermalized particles, such as gravitinos. Small-scale simulations of approximately 183Mpc3, as well as large-scale simulations of approximately 1503Mpc3-1793Mpc3, indicated that the CDM code was successfully modified to simulate WDM through the total dark matter power spectrum and the halo-mass function. Additionally, the large-scale simulations hinted at a positive use of 21cm astronomy for the restriction of keV WDM models, due to the existence of a distinct CDM HI power spectrum as compared to the 0.5keV WDMHI power spectrum. A discernable difference between CDM and keV WDM galactic HI power spectra would provide a step towards a confirmation or falsification of keV WDM models if supplied with a large-scale galactic HI power spectrum study

Made available in DSpace on 2014-12-17T15:15:05Z (GMT). No. of bitstreams: 1 HidalynTCMS.pdf: 3137452 bytes, checksum: c9101961e25b2af76cdd7d74bfe14bb5 (MD5) Previous issue date: 2007-04-26 / Coordena??o de Aperfei?oamento de Pessoal de N?vel Superior / Understanding the way in which large-scale structures, like galaxies, form remains one of the most challenging problems in cosmology today. The standard theory for the origin of these structures is that they grew by gravitational instability from small, perhaps quantum generated, ?uctuations in the density of dark matter, baryons and photons over an uniform primordial Universe. After the recombination, the baryons began to fall into the pre-existing gravitational potential wells of the dark matter. In this dissertation a study is initially made of the primordial recombination era, the epoch of the formation of the neutral hydrogen atoms. Besides, we analyzed the evolution of the density contrast (of baryonic and dark matter), in clouds of dark matter with masses among 104M? ? 1010M?. In particular, we take into account the several physical mechanisms that act in the baryonic component, during and after the recombination era. The analysis of the formation of these primordial objects was made in the context of three models of dark energy as background: Quintessence, ?CDM(Cosmological Constant plus Cold Dark Matter) and Phantom. We show that the dark matter is the fundamental agent for the formation of the structures observed today. The dark energy has great importance at that epoch of its formation / Entender o modo pelo qual estruturas em grande-escala, como gal?xias, se formam permanece um dos problemas mais desafiadores em cosmologia hoje. A teoria padr?o para a origem destas estruturas ? que elas cresceram por instabilidade gravitacional de pequenas, talvez geradas quanticamente, flutua??es na densidade de mat?ria escura, b?rions e f?tons sobre um Universo primordial uniforme. Depois da recombina??o, os b?rions come?aram a cair nos po?os de potencial gravitacional pr?-existentes de mat?ria escura. Nesta disserta??o ? feito inicialmente um estudo da era da recombina??o primordial, a ?poca da forma??o dos ?tomos de hidrog?nio neutro. Al?m disso, analisamos a evolu??o do contraste de densidade (de mat?ria bari?nica e escura), em nuvens de mat?ria escura com massas entre milhares e bilh?es de massas solares. Em particular, na an?lise da componente bari?nica, levamos em conta os v?rios mecanismos f?sicos que ocorrem nela durante e depois da era da recombina??o. A an?lise da forma??o desses objetos primordiais foi feita no contexto de tr?s modelos de energia escura como background ': Quintess?ncia, CDM (Constante Cosmol?gica mais Mat?ria Escura Fria) e Fantasma. Mostramos que a mat?ria escura ? o agente fundamental para forma??o das estruturas observadas hoje. A energia escura tem grande import?ncia na ?poca de sua forma??o