The Late Integrated Sachs-Wolfe effect in Cosmological Simulations

David Ricardo Valencia Díaz
Título conseguido: 
Universidad de Antioquia
Fecha de Grado: 
Viernes, Agosto 22, 2014 - 14:00
Prof. Juan Carlos Muñoz Cuartas, Universidad de Antioquia
Nowadays, the accepted cosmological model is the so called Λ-Cold Dark Matter (ΛCDM), which has been proposed as a model that fits the observations while allows to explain them based on the basis of the therory of General Relativiy. In such model, the Universe is considered to be homogeneous, isotropic and to be composed by diverse components as the baryonic matter, dark matter, radiation and dark energy. The most abundant components are the dark matter and the dark energy, from which the dark energy is the current dominant component. The Cosmic Microwave Background (CMB) is a microwave radiation field that permeates the Universe. In principle, this radiation should be homogeneous, but due to several physical processes, the CMB photons underwent perturbations that induced the formation of several anisotropies. The study of the CMB anisotropies may lead to evidence of the existence of the dark energy, which is associated with the current accelerated expansion of the Universe. In that context, one of those CMB anisotropies is the Integrated Sachs-Wolfe (ISW) effect. The ISW is an effect that the CMB photons experience when they pass through non-stationary overdense or underdense regions, changing their wavelength and energies. Such perturbation in the CMB is associated to the evolution in time of the ravitational potential wells of dark matter structures that form the Large Scale Structures (LSS) and host the galaxies. The aim of this work is to study the late ISW effect in a cosmological simulation, in order to obtain the maps of the anisotropies due to a late ISW effect and study the relation of this temperature fluctuations with the evolution of the gravitational potential wells and the matter density they contain. This is a preliminar study of the ISW effect only in cosmological N -body simulations. The results of this work will allow us to perform a more detailed and extensive study of this effect with both, cosmological simulations and data of galaxy redshift surveys in a future step of the project. What is expected, after a comparison between those exhaustive studies with synthetic and real data, is to detect the signal associated with Integrated Sachs-Wolfe effect, and with that, give a possible evidence of the presence of the dark energy. The numerical and computational methods used to study the late Integrated Sachs-Wolfe effect in this work are based in the Fourier transform of different fields, as the density field, the gravitational potential field and its corresponding time derivative, and the interpolation and numerical integration of the time derivative of the gravitational potential.The results obtained in this work correspond to the late ISW effect in a simulation box of 400h^(−1) Mpc. The methods used to calculate the different fields mentioned before and the maps obtained after the data processing are shown, as well as the maps of the late ISW anisotropy in the simulation box. An interpretation of the results is given and supported with an analysis of the structures of the simulation. Finally, the results are tested through three methods: comparison with linear regime, estimation of the temperature fluctuations along the integration axis and numerical convergence. From those test, it is possible to conclude that the ISW maps obtained with the exact solution and with the linear approximantion show a very good coherence and the linear approximation shows a good behavior in its regime. The numerical convergence test shows that independently of the number of integration steps and of the resolution used, our results present a good convergence. When we compare the temperature fluctuations along the integration axis, our results also shows a good correspondence and behavior with both, the linear approximation values and the different integration steps. Even, when comparing the behavior of the temperature fluctuations along the integration axis with the results obtained in the works of other authors, we obtain similar results. All those tests show a very good processing of the data and that our results are coherent.