AR 16150 (Archival Research)

Thu Jul 18 14:47:52 GMT 2024

Principal Investigator: Keren Sharon
PI Institution: University of Michigan
Investigators (xml)

Title: Hubble constant measurement from cluster-lensed quasars
Cycle: 28

We propose to measure the Hubble constant from time delays in three quasars, strongly lensed by clusters of galaxies. Recent measurements of the H_0 show increasing tension between measurements based on the local distance ladder, and those originating from the cosmic microwave background radiation. The discrepancy between these increasingly precise measurements suggests that the systematics of one or both of these measurements are underestimated, or alternatively, calls for new physics. A third method to measure H_0 is from its scaling with the delay between the arrival times of two or more images of a strongly-lensed variable source (Refsdal 1964), and has been implemented in samples of galaxy-lensed quasars. We propose to explore the feasibility of deriving precise H_0 measurements from cluster-lensed quasars. Quasars lensed by clusters are rare; to date, only five large-separation cluster-lensed quasars have been reported. The longer time delays in cluster-lensed quasars mean that the fractional uncertainty in their time delay measurement is at the few percent level. The large separation reduces systematics from microlensing and baryonic physics. On the other hand, the complexity of the cluster lens is likely to make this measurement more difficult. A careful analysis of systematic and statistical sources of uncertainty is called for; this measurement requires Hubble quality data, which is available for three of the five systems. If successful, this study will establish best practices, map and quantify the sources of error due to lens modeling, and pave the road for utilizing new targets that will be discovered in large ongoing and future surveys.