Dinamica delle galassie SPARC in Gravità Rifratta

In this thesis we studied the dynamics of disk galaxies with Refracted Gravity (RG), a promising theory of modified gravity. This theory introduces a gravitational permittivity in the Poisson equation for the purpose of overcoming the kinematic and dynamic anomalies observed in cosmic structures, without the need of dark matter. In this regard, the SPARC sample is an important test bed for investigating RG on galaxy scales, as it spans wide ranges of galaxy types and properties. By modeling the mass distribution of 43 SPARC galaxies with two free parameters, namely the stellar mass-to-light ratio Υ and the disk thickness hz , and assuming a three-parameter function of the local density for the gravitational per mittivity, we built kinematic models for RG. We found that RG is indeed able to describe the observed rotation curves, with consistent values of Υ and hz . Moreover, the three RG parameters defining the gravitational permittivity are also in agreement with previous work on the DMS sample, supporting the existence of a unique set of these parameters that might properly describe the kinematics of the entire sample. Nevertheless, RG can only partly reproduce the Radial Acceleration Relation (RAR), a tight correlation that behaves like a natural law for galaxies. RG, in fact, underestimates the RAR at intermediate accelerations and predicts an intrinsic scatter of 0.12 dex, which is at odds with the null intrinsic scatter observed for the SPARC galaxies. In addition, although several significant correlations between the residuals around the RAR and the galaxy properties are actually present in the SPARC sample, they are not sufficient to explain the strong correlations expected by RG, as they are considerably increased or even introduced where none exists. Therefore, reproducing the observed properties of the RAR is challenging for RG, at this stage of investigation of the theory, but future work might shed light on the origin of these discrepancies.