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 allow measurement of these scales to infer 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 already become competitive 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). Recently, I have analyzed one new lens system to infer H_0 with the highest precision from a single lens system to date. This new measurement brings the combined uncertainty from time-delay cosmography to 2% - which is comparable to the SH0ES measurement - and increases the tension with the early-Universe probes. Lastly, I will present the future roadmap of time-delay cosmography to independently reach 1% precision within a few years.
Speaker: Anowar Shajib, UCLA
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