Astro Lunch Seminar

Speaker: Anowar Shajib (the University of Chicago)
Title: Measuring the Hubble constant with strong-lensing time delays: past, present, and future
Date (JST): Tue, Nov 01, 2022, 11:00 - 12:00
Place: Zoom
Abstract: Strong-lensing time delay is a probe of the Hubble constant that is independent of other conventional methods such as the cosmic distance ladder and the cosmic microwave background radiation. The recent tension between the latter two probes highlights the importance of such an additional and independent probe to resolve the tension. I will overview the current status of the Hubble constant measurement using time delays and present the future roadmap for independently achieving ~1% precision in the Hubble constant to resolve the tension with 5sigma confidence level. The TDCOSMO (previously known as the H0LiCOW) collaboration has analyzed seven time-delay lenses to achieve a 2% precision in the Hubble constant with assumptions on the lensing mass profile such as the power law. This measurement agrees with the Cepheid-calibrated cosmic distance ladder measurement. However, if the power-law model assumption is relaxed for the lensing galaxy’s mass distribution, the well-known mass-sheet degeneracy leads to 9% uncertainty in the resultant Hubble constant. To break the mass-sheet degeneracy in order to achieve ~1% precision in the Hubble constant without a model assumption, spatially resolved velocity dispersion, or standardizable unlensed brightness of strongly lensed supernovae, or both will be crucial in the upcoming decade.