S21A0128
S21A0128
Time-delay cosmography is a powerful technique to determine the Hubble constant (H0), and is independent of the cosmic microwave background (CMB) and late-Universe probes such as type Ia supernovae calibrated by the distance ladder. The latest results from the H0LiCOW/TDCOSMO collaboration, under realistic assumptions of lens mass distributions, find a value of H0 that is in agreement with the latest Cepheid-calibrated distance ladder results, but are >3σ higher than the Planck CMB inference for a flat ΛCDM cosmology. If unresolved, this discrepancy could force the rejection of the flat ΛCDM model in favor of new physics. It is crucial to enlarge the lensing sample, both to improve the precision in H0 and further investigate residual systematics. In this proposal, we aim to use Subaru/FOCAS spectroscopy to measure the lens galaxy redshifts for eight new lensed quasars, which will make them useful for time-delay cosmography and improve the overall constraints on H0 by a factor of ∼√N. As a bonus ancillary science goal, these observations will also make these lenses useful for studying dark matter substructure with the flux-ratio anomaly technique, which can place constraints on the properties of dark matter.
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