The origin and dynamics of the cool circumgalactic gas around low-redshift galaxies

The evolution of galaxies in the Universe is strongly linked to the gas that resides in their halos, the circumgalactic medium, or CGM. This is a complex system, composed of phases at very different temperatures that coexist with each other, from the hot CGM, a diffuse gas with temperatures between 1 and ten million Kelvin; to the cool CGM, likely composed of a variety of clouds with temperatures of about ten thousand Kelvin. The latter represents, in particular, the main focus of this Thesis. This medium has been extensively observed in the last decades, with detections up to very large distances from the central galaxies. This cool gas is particularly important, since, if accreting onto the central galaxies, it might fuel the formation of new stars and therefore regulate the evolution of galaxies themselves. However, the origin, dynamics and fate of these cool clouds are to date still debated. In this Thesis, we have found, comparing the predictions of our semi-analytical models with recent observational data, that the cool CGM is most likely originated, in the halos of both elliptical and disk galaxies, from the accretion from external gas (known as intergalactic medium). Finally, through the use of idealized numerical simulations, we have shown that the fate of these inflowing cool clouds is to evaporate into the hot CGM before being able to reach the central galaxies.