Modified Gravity and Large Scale Flows

TL;DR

This paper compares standard gravity and MONDian gravity in explaining large-scale cosmic flows, introducing a new diagnostic to test their consistency with observed velocity fields, and finds that MONDian gravity does not match observations.

Contribution

It introduces the velocity angular correlation function as a scale-independent diagnostic for peculiar velocity fields and assesses the compatibility of modified gravity with large-scale structure data.

Findings

Standard gravity aligns with observed velocities

MONDian gravity does not match large-scale flow data

Modified gravity would need to decay faster than r^-1 at large distances

Abstract

Reconstruction of the local velocity field from the overdensity field and a gravitational acceleration that falls off from a point mass as r^-2 yields velocities in broad agreement with peculiar velocities measured with galaxy distance indicators. MONDian gravity does not. To quantify this, we introduce the velocity angular correlation function as a diagnostic of peculiar velocity field alignment and coherence as a function of scale. It is independent of the bias parameter of structure formation in the standard model of cosmology and the acceleration parameter of MOND. A modified gravity acceleration consistent with observed large scale structure would need to asymptote to zero at large distances more like r^-2, than r^-1.