Time-delay Cosmography: Increased Leverage with Angular Diameter Distances

TL;DR

Incorporating angular diameter distances into time-delay cosmography significantly enhances constraints on cosmological parameters, especially in breaking degeneracies related to dark energy and curvature, making these systems more powerful than previously thought.

Contribution

This study demonstrates that including angular diameter distances with time-delay distances improves cosmological parameter constraints from lensing systems.

Findings

Adding angular diameter distance improves dark energy equation of state constraints by 30%.

Including this distance doubles the precision on the Hubble constant.

Time-delay systems are more powerful for cosmology than earlier forecasts suggested.

Abstract

Strong lensing time-delay systems constrain cosmological parameters via the so-called time-delay distance and the angular diameter distance to the lens. In previous studies, only the former information was used. In this paper, we show that the cosmological constraints improve significantly when the latter information is also included. Specifically, the angular diameter distance plays a crucial role in breaking the degeneracy between the curvature of the Universe and the time-varying equation of state of dark energy. Using a mock sample of 55 bright quadruple lens systems based on expectations for ongoing/future imaging surveys, we find that adding the angular diameter distance information to the time-delay distance information and the cosmic microwave background data of Planck improves the constraint on the constant equation of state by 30%, on the time variation in the equation of state by a factor of two, and on the Hubble constant in the flat $\Lambda$CDM model by a factor of two. Therefore, previous forecasts for the statistical power of time-delay systems were significantly underestimated, i.e., time-delay systems are more powerful than previously appreciated.