Anowar Shajib (UCLA) -- Measurement of the Hubble Constant from Strongly Lensed Quasars


The recent tension between early- and late-Universe measurements of the Hubble constant highlights the necessity for independent and precise probes such as the time-delay cosmography. The measured time-delays between the lensed images of a background quasar depend on the absolute physical scales in the lens configuration. Thus, they provide an anchor for these scales to measure the Hubble constant, H_0. Due to a number of great advancements over the past decade in both the data quality and modeling techniques, the measurement of H_0 from the time-delays has started to fulfill its promise to soon be competitive, if not yet, with other traditional methods such as the cosmic distance ladder. This is evident from the recent 2.4% blind measurement of H_0 from only six lenses (Wong et al. 2019). Simulation shows that a sample of nine lenses shrinks the uncertainty on this measurement to 2% (Shajib et al. 2018). I am currently analyzing two additional lens systems. I will present an updated measurement of the Hubble constant combining the newly analyzed systems with the old sample of six. In addition, I will present the future roadmap of time-delay cosmography to independently reach 1% precision within a few years.