Cosmological parameters from strong gravitational lenses

Recent measurements of the Hubble Constant (H_0) through distance ladder techniques have revealed a noticeable tension with the Planck H_0 value that was obtained under the assumption of the cosmological “standard model”, i.e., a flat Lambda cold dark matter cosmology. Is this tension an indication that modifications to the standard model are necessary, or is it the sign of unknown systematic effects in one or both of the techniques? To address this question requires additional high-precision measurements with techniques that are independent of the distance ladder. The time delay strong lensing technique, in which gravitational lensing by a massive galaxy produces multiple images of a time-variable quasar, fulfills these requirements. I will present recent results from the H0licow program, in which the analysis of just three time-delay strong lenses has produced a 3.8% measurement of H_0, and discuss the implications for other cosmological parameters, including those describing dark energy. I will also discuss the future prospects of this technique in the era of large sky surveys and extremely large telescopes.

Speaker: Chris Fassnacht, UC Davis

Room LBL 50-5132