Memoria presentada por el Licenciado
Pier Paolo Ponente y
dirigida por
Jose Maria Diego Rodriguez, Doctor en Ciencias Físicas y
Cientifico titular del Consejo Superior de Investigaciones Científicas.The main motivation of this thesis is to study the distant Universe through alternative windows which are emerging in the most recent years. At high redshift, the large scale structure (LSS) undergoes an interesting phase called the reinoziation where the neutral matter gets ionized around the first generation of stars. This ionized medium can emit interesting signals among which I am interested in the weak free-free emission from diffuse gas and galaxy clusters
present in the Universe after the era of the reionization. N-body simulations of this distant epoch can help understand the properties of the free-free and other siganls emerging from the reionization time. The free-free emission has been largely ignored in the literature with very few works paying attention to it. Part of this thesis will focus also on synchrotron signal from normal galaxies.
Recent developements in technology start to reach the sensitivity needed to discern this weak signals from other more predominant ones. Also, my thesis will focus on the possible observational evidence of this signal, in particular in the excess signal found by the ARCADE2 experiment at radio wavelengths that could be partially explained by free-free emission from the reionization time.
ARCADE2 is a balloon-borne mission whose goal is to measure the radiobackground at frequencies lower than thiose explored by past and current Cosmic Microwave Background experiments. This regime of low frequencies are sensitive to interesting physical phenomena including some that coccured after the inflationary time and before the matter-radiation decoupling. The results of the
ARCADE2 are surprising, with a significant excess of signal over previous estimations of the microwave-radio background temperature distortion (as measured by COBE/FIRAS). The authors claim that the results are free from systematics and that the excess signal is purely extragalactic, suggesting that freefree and synchrotron emissions could be the cause. This thesis explores both
possibilities and throughs some light into this unsolved puzzle.The physics involved in the sysnchrotron is far more complicated than in the free-free caee,
needing a specific model for the Initial Mass Function (IMF), for the cosmic star formation rate (SFR), the rate of supernovae production and how they contribute to the magnetic field in galaxies. For these reasons, I concentrate my efforts on building a phenomenological model for the synchrotron emission,
who shares some underlying mechanisms with the free-free model. The model is the first one (or one of the first ones) that uses the SFR to estimate the signal observed by ARCADE2 . To achieve my goals, I make use of both analytical models (like the mass functions
of Press-Schecther and Sheth-Tormen) and numerical simulations (making
my own simulations with the GADGET-2 code). The study of the radio Universe in the low GHz band offers a new window to
explore the high redshift Universe. The results of my thesis will be relevant for future facilities such as ALMA as it deals with signals that could be potentially
be studied with this facility. My thesis work is completed with a study of the lensing problem. Gravitational
lenses are an interesting tool to understand our Universe. On one hand they offer one of the best scenarios to see dark matter through their gravitational
effects and on the other hand thay act as magnifying lenses that enhanced the flux of the background galaxies making it easier to detect them. This second feature is particularly interesting to study the first population of galaxies that emerge after the reionization time. I explore the capabilities of the gravitational
mass reconstruction by studying one partiocular case that has triggered great
debate in the last years, the galaxy cluster CL00254 and its alleged ring of dark
matter. I explore the possible systematics in the lensing reconstruction of this
cluster.Peer Reviewe
