The contribution of star-forming galaxies to the cosmic radio background

Recent measurements of the temperature of the sky in the radio band, combined with literature data, have convincingly shown the existence of a cosmic radio background with an amplitude of $\sim 1$ K at 1 GHz and a spectral energy distribution that is well described by a power law with index $\alpha \simeq -0.6$. The origin of this signal remains elusive, and it has been speculated that it could be dominated by the contribution of star-forming galaxies at high redshift \change{if the far infrared-radio correlation $q(z)$ evolved} in time. \change{We fit observational data from several different experiments by the relation $q(z) \simeq q_0 - \beta \log(1+z)$ with $q_0 = 2.783 \pm 0.024$ and $\beta = 0.705 \pm 0.081$ and estimate the total radio emission of the whole galaxy population at any given redshift from the cosmic star formation rate density at that redshift. It is found that} star-forming galaxies can only account for $\sim$13 percent of the observed intensity of the cosmic radio background.Comment: 5 pages, 3 figure

The cosmological free-free signal from galaxy groups and clusters

Using analytical models and cosmological N-body simulations, we study the free-free radio emission from ionized gas in clusters and groups of galaxies. The results obtained with the simulations are compared with analytical predictions based on the mass function and scaling relations. Earlier works based on analytical models have shown that the average free-free signal from small haloes (galaxies) during and after the reionization time could be detected with future experiments as a distortion of the CMB spectrum at low frequencies ($\nu <$ 5 GHz). We focus on the period after the reionization time (from redshift $z=0$ up to $z=7$) and on haloes that are more massive than in previous works (groups and clusters). We show how the average signal from haloes with $M > 10^{13} h^{-1} M_{\odot}$ is less than 10% the signal from the more abundant and colder smaller mass haloes. However, the individual signal from the massive haloes could be detected with future experiments opening the door for a new window to study the intracluster medium.Comment: 11 pages, 7 figure

Estudio del universo a alto redshift con simulaciones de N-cuerpos

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