The kinematic dipole in galaxy redshift surveys

TL;DR

This paper derives formulas for the kinematic dipole in galaxy redshift and intensity surveys, exploring its potential as a cosmological probe and its relation to the CMB dipole.

Contribution

It provides new theoretical formulas for the matter dipole amplitude, including relativistic effects, and discusses its implications for cosmology.

Findings

The matter dipole amplitude can exceed the CMB dipole.

Redshift dependence of the dipole encodes universe evolution.

Future surveys can measure the matter dipole direction accurately.

Abstract

In the concordance model of the Universe, the matter distribution - as observed in galaxy number counts or the intensity of line emission (such as the 21cm line of neutral hydrogen) - should have a kinematic dipole due to the Sun's motion relative to the CMB rest-frame. This dipole should be aligned with the kinematic dipole in the CMB temperature. Accurate measurement of the direction of the matter dipole will become possible with future galaxy surveys, and this will be a critical test of the foundations of the concordance model. The amplitude of the matter dipole is also a potential cosmological probe. We derive formulas for the amplitude of the kinematic dipole in galaxy redshift and intensity mapping surveys, taking into account the Doppler, aberration and other relativistic effects. The amplitude of the matter dipole can be significantly larger than that of the CMB dipole. Its redshift dependence encodes information on the evolution of the Universe and on the tracers, and we discuss possible ways to determine the amplitude.