Kinematic dipole detection with galaxy surveys: forecasts and requirements

TL;DR

This paper forecasts the potential of future wide-sky galaxy surveys to measure the kinematic dipole, testing the standard cosmological model and addressing biases from local structures.

Contribution

It provides forecasts for statistical errors and systematic biases in kinematic dipole measurements using deep galaxy surveys with specific sky coverage and galaxy counts.

Findings

A survey with 75% sky coverage and 30 million galaxies can detect the dipole at 5σ.

Median redshift of at least 0.75 minimizes local-structure bias.

Deep surveys are essential for unbiased kinematic dipole measurement.

Abstract

Upcoming or future deep galaxy samples with wide sky coverage can provide independent measurement of the kinematic dipole - our motion relative to the rest frame defined by the large-scale structure. Such a measurement would present an important test of the standard cosmological model, as the standard model predicts the galaxy measurement should precisely agree with the existing precise measurements made using the CMB. However, the required statistical precision to measure the kinematic dipole typically makes the measurement susceptible to bias from the presence of the local-structure-induced dipole contamination. In order to minimize the latter, a sufficiently deep survey is required. We forecast both the statistical error and the systematic bias in the kinematic dipole measurements. We find that a survey covering $\sim 75\%$ of the sky in both hemispheres and having $\sim 30$ million galaxies can detect the kinematic dipole at $5\sigma$, while its median redshift should be at least $z_{med} \sim 0.75$ for negligible bias from the local structure.