Gravitational lensing: A Swiss knife to dissect galaxies !

Strong gravitational lensing is a major tool of modern extragalactic astrophysics. The lensing phenomenon can be used as a natural telescope to magnify the distant Universe, a scale to weigh galaxies, and even a ladder to measure the expansion rate of the Universe. In this talk, we will explore the properties of galaxies as disclosed with the lensing phenomenon. First, I will explain how we can infer the dark matter content of a lensing galaxy based on the deformed images of a lensed source. Then, we will see how, with a mass model of the lensing galaxy in hands, we can reconstruct high spatial resolution images of galaxies hosting quasars. Finally, we will travel further into the heart of galaxies, taking advantage of the light deflection produced by the individual stars in a lensing galaxy, to zoom into accreting black holes. Owing to the so called microlensing effect, we will unveil the properties of the gas in the direct vicinity of galaxies central engine.