Speaker
Description
The Vera C. Rubin Observatory (LSST) will discover thousands of new multiply imaged quasars and supernovae (Oguri & Marshall 2010). In P3 and P4, we have proposed monitoring observations with the VST of quasars multiply lensed by galaxies and galaxy clusters, that will belong to the final LSST sample, to accurately measure the multiple image light curves, thus their time delays. We aim at using these time delays as an important and complementary tool to measure the expansion rate and the geometry of the Universe. In detail, we have performed a high-cadence and high S/N ratio monitoring campaign with the VST. Time-delay cosmography is based on well-know physics (General Relativity) and is a single-step technique that can yield competitive and independent estimates of the values of the cosmological parameters, without any complex calibration. I will give an overview of the status of the programme and will show the first promising results. The final outcomes of this study will help clarify whether the current, hotly debated tension on the value of $H_{0}$ must be ascribed to intriguing new physics or to significant systematic effects neglected so far, and improve by 40% the Figure of Merit of any stage-IV cosmological survey (LSST, Euclid, etc.). In addition, leveraging the large field of view of the VST, we will perform a search for Type Ia supernovae (SN Ia) exploding in cluster member galaxies. The daily sampling rate of the light curves will provide independent estimates of the luminosity distances of the SN Ia galaxy hosts, and thus of the lens clusters. Moreover, we will also estimate the rate of SNe Ia in galaxy clusters, which can shed light on the progenitors and physics of SNe Ia. Over the VST wide field of view, the same data will provide deep imaging, in good seeing conditions, that will allow us to build high-quality weak lensing mass maps and to detect serendipitous new transients. I will conclude with some examples of possible ancillary science, thanks to the measured light curves of several variable stars and AGNs identified in the targeted fields.