New cosmological constraints from a weak lensing analysis of the AMICO galaxy cluster catalogue in the Kilo-Degree Survey

The spatial and dynamical properties of the large-scale structures of the Universe provide one of the most powerful probes to constrain the cosmological framework. In particular, the gravitational lensing of galaxy clusters can be efficiently exploited to constrain the main cosmological parameters. In this work, we present new cosmological constraints inferred from the analysis of weak lensing shear data, extracted from the KiDS-DR3 photometric survey. The galaxy cluster sample used in this work was extracted using the Adaptive Matched Identifier of Clustered Objects (AMICO) algorithm (Bellagamba et al., 2018) by Maturi et al., 2018. This cluster catalogue has been constructed by selecting only the objects with signal-to-noise ratio larger than 3.5, in the redshift range 0.1 < z < 0.6. The final sample consists of 6972 galaxy clusters in total. A full Bayesian analysis (MCMCs) is performed to model the stacked shear profiles. We mainly exploit the clusters 2-halo term to constrain the matter density contrast Ω_m. We find that the adopted modelling is successful to assess both the cluster masses and the matter density parameter, when fitting shear profiles up to the largest scales probed. The derived masses of the cluster samples are in good agreement with those estimated by Bellagamba et al. (2019). Our work confirms the reliability of AMICO and of the KiDS-DR3 data. Moreover, our results provide a strong observational evidence of the 2-halo signal in the stacked gravitational lensing of galaxy clusters, and demonstrate the reliability of this probe for constraining cosmological model parameters. The main result of this thesis work is a new, robust constraint on Ω_m , assuming a flat ΛCDM cosmology. Specifically, we find a Ω_m= 0.285 ± 0.023, estimated from the full posterior probability distribution. This value is consistent and competitive with that estimated by WMAP9 (0.273 ± 0.049), but slightly in tension with Planck18 constraints, (0.317 ± 0.008).