Cosmological impact of redshift drift measurements

TL;DR

Redshift drift measurements are a promising, model-independent way to probe cosmology, with different methods offering trade-offs in constraining matter density and dark energy parameters, influencing instrument design.

Contribution

This paper compares the effectiveness of various redshift drift measurement methods for constraining cosmological parameters, highlighting their strengths and limitations.

Findings

ELT constraints are stronger with longer baselines.

Cosmic accelerometer outperforms ELT with identical baselines.

Differential redshift drift better constrains dark energy than matter density.

Abstract

The redshift drift is a model-independent probe of fundamental cosmology, but choosing a fiducial model one can also use it to constrain the model parameters. We compare the constraining power of redshift drift measurements by the Extremely Large Telescope (ELT), as studied by Liske {\it et al.} (2008), with that of two recently proposed alternatives: the cosmic accelerometer of Eikenberry {\it et al.} (2020), and the differential redshift drift of Cooke (2020). We find that the cosmic accelerometer with a 6-year baseline leads to weaker constraints than those of the ELT (by $60\%$), but with identical time baselines it outperforms the ELT by up to a factor of 6. The differential redshift drift always performs worse that the standard approach if the goal is to constrain the matter density, but it can perform significantly better than it if the goal is to constrain the dark energy equation of state. Our results show that accurately measuring the redshift drift and using these measurements to constrain cosmological parameters are different merit functions: an experiment optimized for one of them will not be optimal for the other. These non-trivial trade-offs must be kept in mind as next generation instruments enter their final design and construction phases.