Cosmic flow around local massive galaxies

TL;DR

This study estimates the zero-velocity surface radius around local massive galaxies using galaxy velocity and distance data, revealing that their outskirts contain little hidden mass beyond the virial radius.

Contribution

The paper introduces a method to determine the zero-velocity surface radius around nearby groups, incorporating the cosmological constant, and provides mass estimates consistent with standard cosmological models.

Findings

Estimated zero-velocity radius for the Local Group is 0.91 Mpc.

Total mass within the zero-velocity radius is about 1.6 x 10^12 solar masses.

Mass estimates suggest little hidden mass outside the virial radius.

Abstract

Aims. We use accurate data on distances and radial velocities of galaxies around the Local Group, as well as around 14 other massive nearby groups, to estimate their radius of the zero-velocity surface, $R_0$, which separates any group against the global cosmic expansion. Methods. Our $R_0$ estimate was based on fitting the data to the velocity field expected from the spherical infall model, including effects of the cosmological constant. The reported uncertainties were derived by a Monte Carlo simulation. Results. Testing various assumptions about a location of the group barycentre, we found the optimal estimates of the radius to be $0.91\pm0.05$~Mpc for the Local Group, and $0.93\pm0.02$~Mpc for a synthetic group stacked from 14 other groups in the Local Volume. Under the standard Planck model parameters, these quantities correspond to the total mass of the group $\sim (1.6\pm0.2) 10^{12} M_{\odot}$. Thus, we are faced with the paradoxical result that the total mass estimate on the scale of $R_0 \approx (3- 4) R_{vir}$ is only $~60$% of the virial mass estimate. Anyway, we conclude that wide outskirts of the nearby groups do not contain a large amount of hidden mass outside their virial radius.