Time Delay Cosmography

TL;DR

Time delay cosmography uses gravitational lensing time delays to measure cosmological distances, requiring precise observations and modeling, with recent progress enabling competitive cosmological inferences and future potential with larger samples.

Contribution

This paper reviews 15 years of progress in time delay cosmography, highlighting advancements and future prospects for larger lens samples and improved cosmological measurements.

Findings

First competitive cosmological inferences made using time delays

Progress in modeling gravitational potentials and line-of-sight effects

Potential for significant improvements with upcoming larger samples

Abstract

Gravitational time delays, observed in strong lens systems where the variable background source is multiply-imaged by a massive galaxy in the foreground, provide direct measurements of cosmological distance that are very complementary to other cosmographic probes. The success of the technique depends on the availability and size of a suitable sample of lensed quasars or supernovae, precise measurements of the time delays, accurate modeling of the gravitational potential of the main deflector, and our ability to characterize the distribution of mass along the line of sight to the source. We review the progress made during the last 15 years, during which the first competitive cosmological inferences with time delays were made, and look ahead to the potential of significantly larger lens samples in the near future.