Department Seminar by Hyungsuk Tak

Please Note: This seminar will be given online.

Time Delay Cosmography Towards The Hubble Constant

The Hubble constant is a core cosmological parameter that represents the current expansion rate of the Universe. However, estimates for this quantity have been inconsistent. Astronomers have been concerned about this inconsistency, developing various methods to estimate the Hubble constant independently. One of such independent methods is time delay cosmography. This method is based on strong gravitational lensing, an effect that multiple images of the same astronomical object appear in the sky because paths of the images (from the object to the Earth) are bent by the strong gravitational field of an intervening galaxy. This strong gravitational lensing effect produces two types of the data; multiple time series data of brightness, and imaging data of lensing galaxy and lensed source. We use the time series data to infer time delays between the arrival times of the multiply-lensed images, and the imaging data to estimate gravitational potential of the lensing galaxy. The Hubble constant can be estimated with these two quantities. In this talk, I explain the relationship among the three components, time delay, gravitational potential, and the Hubble constant, introducing data analytic challenges and our collaborative efforts toward the Hubble constant estimation.