Vincoli a tasso di crescita e clustering delle strutture cosmiche usando una tecnica indipendente da modelli applicata a simulazioni di Intensity Mapping

During the second half of the XX century, cosmological data, in- terpreted with General Relativity and the Friedmann-Robinson-Walker- Lemaitre homogeneous and isotropic metric, have led to the so-called ΛCDM model. The picture consists of a Universe which is expanding under the influence of a late-time dark energy and whose matter content is for the most part non-baryonic dark matter. Since the nature of both dark energy and dark matter are far from well understood, new data and new analysis methods are needed. Our goal is to measure two fundamental physical quantities that can set limits to the cosmological parameters of the ΛCDM model: the clustering and the growth rate of cosmic structures. We want to do that using a spherical harmonics decomposition, since the observations are projected onto the celestial sphere form Intensity Mapping. IM aims to measure matter distribution in the Universe using line emitted in radio band from high density regions. This method allows cosmologists to survey the sky way deeper than the more renowned optical surveys, but the results present mild noises and intense foregrounds. To obtain a clean signal Spinelli and colleagues have simulated some cosmological HI signal (given a set of ΛCDM parameters), they added artificial contamination and they tried to obtain back the original signal. The goal is to develop a validated method to be applied at future radio survey (for example from SKA). In the present work, we describe the harmonic decomposition and we implement and test a template-fitting pipeline created with the Einsten- Boltzmann solver CAMB (Tanidis & Camera, 2021) and making use of the Markov Chain Monte Carlo technique to measure bσ8 and f σ8 from a binned IM simulation (Spinelli et al., 2021).