The Redshift Difference in Gravitational Lensed Systems: A Novel Probe of Cosmology

TL;DR

This paper proposes a new method to probe cosmology by measuring redshift differences in gravitational lens systems, offering a faster alternative to redshift drift observations for constraining matter and dark energy densities.

Contribution

The study introduces a novel approach using redshift differences in lens systems to determine cosmological parameters without long-term observations.

Findings

Redshift difference is sensitive to matter and dark energy densities.

The method is independent of the Hubble constant.

Approximately 1,000 lens systems are needed for robust parameter estimation.

Abstract

The exploration of the redshift drift, a direct measurement of cosmological expansion, is expected to take several decades of observation with stable, sensitive instruments. We introduced a new method to probe cosmology which bypasses the long-period observation by observing the redshift difference, an accumulation of the redshift drift, in multiple-image gravitational lens systems. With this, the photons observed in each image will have traversed through different paths between the source and the observer, and so the lensed images will show different redshifts when observed at the same instance. Here, we consider the impact of the underlying cosmology on the observed redshift difference in gravitational lens systems, generating synthetic data for realistic lens models and exploring the accuracy of determined cosmological parameters. We show that, whilst the redshift difference is sensitive to the densities of matter and dark energy within a universe, it is independent of the Hubble constant. Finally, we determine the observational considerations for using the redshift difference as a cosmological probe, finding that one thousand lensed sources are enough to make robust determinations of the underlying cosmological parameters. Upcoming cluster lens surveys, such as the Euclid, are expected to detect a sufficient number of such systems.