A prediction for anisotropies in the nearby Hubble flow

TL;DR

This paper predicts low-redshift anisotropic signatures in the universe's expansion, identifying a dipolar pattern in distance measurements and a quadrupolar pattern in redshift drift, based on relativistic simulations.

Contribution

It introduces a novel approach using quiet universe models to simplify the analysis of anisotropies in the Hubble flow, reducing degrees of freedom and predicting specific anisotropic signatures.

Findings

A dominant dipole in the distance-redshift relation aligned with large-scale density gradients.

A quadrupole in redshift drift anisotropy sourced by electric Weyl curvature.

Predictions are testable with current and upcoming cosmological surveys.

Abstract

We assess the dominant low-redshift anisotropic signatures in the distance-redshift relation and redshift drift signals. We adopt general-relativistic irrotational dust models allowing for gravitational radiation -- the `quiet universe models' -- which are extensions of the silent universe models. Using cosmological simulations evolved with numerical relativity, we confirm that the quiet universe model is a good description on scales larger than those of collapsing structures. With this result, we reduce the number of degrees of freedom in the fully general luminosity distance and redshift drift cosmographies by a factor of $\sim 2$ and $\sim 2.5$, respectively, for the most simplified case. We predict a dominant dipolar signature in the distance-redshift relation for low-redshift data, with direction along the gradient of the large-scale density field. Further, we predict a dominant quadrupole in the anisotropy of the redshift drift signal, which is sourced by the electric Weyl curvature tensor. The signals we predict in this work should be tested with present and near-future cosmological surveys.