Critical points of the cosmic velocity field and the uncertainties in the value of the Hubble constant

TL;DR

This paper suggests that focusing on critical points of the peculiar velocity field, such as voids and saddle points, can reduce uncertainties in measuring the Hubble constant, based on simulation evidence.

Contribution

It introduces a novel method of selecting observational data around velocity critical points to improve the precision of the Hubble constant measurement.

Findings

Regions around critical points are stable over time.

Restricting analysis to these regions reduces variance in Hubble flow measurements.

Simulation results support the effectiveness of this approach.

Abstract

The existence of critical points for the peculiar velocity field is a natural feature of the correlated vector field. These points appear at the junctions of velocity domains with different orientations of their averaged velocity vectors. Since peculiar velocities are the important cause of the scatter in the Hubble expansion rate, we propose that a more precise determination of the Hubble constant can be made by restricting analysis to a subsample of observational data containing only the zones around the critical points of the peculiar velocity field, associated with voids and saddle points. On large-scales the critical points, where the first derivative of the gravitational potential vanishes, can easily be identified using the density field and classified by the behavior of the Hessian of the gravitational potential. We use high-resolution N-body simulations to show that these regions are stable in time and hence are excellent tracers of the initial conditions. Furthermore, we show that the variance of the Hubble flow can be substantially minimized by restricting observations to the subsample of such regions of vanishing velocity instead of aiming at increasing the statistics by averaging indiscriminately using the full data sets, as is the common approach.