Discovering multiply-imaged quasars with Gaia

Gaia was mainly designed for the study of stars in our Galaxy. However, by continuously scanning the entire sky, it also provides informations on all kind of objects that fall in its fields of view, including extragalactic objects. Amongst these extragalactic sources, quasars stand out to be some of the most peculiar objects that Gaia observe. Beside the fact that they play a crucial role in fixing the Gaia Celestial Reference Frame, they also have their intrinsic interest in cosmology.

One of their important application occurs when a massive galaxy stands along the line of sight joining the quasar and the observer as, in this case, multiple images of this quasar may form. The time delays measurement between these lensed images then provide a reliable estimation of H0 that is independent of the commonly used cosmic distance ladder.

We describe here how the precise relative positions and magnitudes, as provided by Gaia, can be used in order to probe the lensing nature of clusters of objects coming from the Gaia DR2. We present some newly discovered lenses that were spectroscopically confirmed in recent follow-up observations. Finally, we see how the upcoming Gaia data releases will further allow to increase the number of discovered lenses by one order of magnitude as compared to the number of those that are presently known.