Direction and redshift drifts for general observers and their applications in cosmology

TL;DR

This paper derives general formulas for redshift and direction drifts for any observer in various cosmological models, aiding the interpretation of high-precision astrometric data for probing the universe's structure and dynamics.

Contribution

It provides a comprehensive derivation of redshift and direction drifts applicable to general observers in both standard and anisotropic cosmological models, including first-order perturbations.

Findings

Direction drift splits into parallax and aberration components.

Peculiar velocity contributes mainly as a dipole in multipolar decomposition.

Anisotropic shear influences the quadrupole component.

Abstract

High precision astrometry now enables to measure the time drift of astrophysical observables in real time, hence providing new ways to probe different cosmological models. This article presents a general derivation of the redshift and direction drifts for general observers. It is then applied to the standard cosmological framework of a Friedmann-Lemaitre space- time including all effects at first order in the cosmological perturbations, as well as in the class of spatially anisotropic universe models of the Bianchi I family. It shows that for a general observer, the direction drift splits into a parallax and an aberration drifts and order of magnitude estimates of these two components are provided. The multipolar decomposition of the redshift and aberration drifts is also derived and shows that the observer's peculiar velocity contributes only as a dipole whereas the anisotropic shear contributes as a quadrupole.