A Slight Excess of Large Scale Power from Moments of the Peculiar Velocity Field

TL;DR

This paper investigates the implications of high bulk flow measurements on the matter power spectrum, finding a slight excess of large-scale power but overall consistency with LCDM when considering multiple velocity moments.

Contribution

It demonstrates that including shear and octupole moments of the velocity field reconciles high bulk flow measurements with standard cosmological models.

Findings

High bulk flow suggests higher power spectrum amplitude when analyzing only the dipole.

Including shear and octupole moments aligns results with LCDM.

Slight excess of power on scales around 1 Gpc observed.

Abstract

The peculiar motions of galaxies can be used to infer the distribution of matter in the Universe. It has recently been shown that measurements of the peculiar velocity field indicates an anomalously high bulk flow of galaxies in our local volume. In this paper we find the implications of the high bulk flow for the power spectrum of density fluctuations. We find that analyzing only the dipole moment of the velocity field yields an average power spectrum amplitude which is indeed much higher than the LCDM value. However, by also including shear and octupole moments of the velocity field, and marginalizing over possible values for the growth rate, an average power spectrum amplitude which is consistent with LCDM is recovered. We attempt to infer the shape of the matter power spectrum from moments of the velocity field, and find a slight excess of power on scales ~ h-1 Gpc.