Galaxy groups in the presence of Cosmological Constant: Increasing the Masses of Groups

TL;DR

This paper extends the definitions of zero radial acceleration and turnaround surfaces in galaxy groups considering the cosmological constant, revealing that it increases estimated group masses by 5-10% and emphasizing the role of local cosmic expansion.

Contribution

It introduces generalized definitions of key surfaces in galaxy groups within an expanding universe with a cosmological constant, and applies them to estimate group masses more accurately.

Findings

Inclusion of the cosmological constant increases galaxy group mass estimates by 5-10%.

The Local Group's mass is estimated at approximately 2.47 x 10^{12} solar masses.

The analysis highlights the significance of local cosmic expansion in understanding cosmic flow.

Abstract

The boundaries of galaxy groups and clusters are defined by the interplay between the Newtonian attractive force and the decoupling from the local expansion of the Universe. This work extends the definition of a zero radial acceleration surface (ZRAS) and the turnaround surface (TS) for a general distribution of the masses in an expanding background, governed by the cosmological constant. We apply these definitions to different galaxy groups in the local Universe, mapping these groups up to ten megaparsec distances. We discuss the dipole and the quadrupole rate for the Local Group of Galaxies and the implementations on the Hubble diagram correction and galaxy groups virialization. With these definitions, we present the surfaces showing the interplay between the local expansion vs the local Newtonian attraction for galaxy groups in the local Universe. Further, we estimate the masses of different galaxy groups and show that the inclusion of the Cosmological Constant in the analysis predicts these masses to be higher by 5-10\%. For instance the Local Group of Galaxies is estimated to be $(2.47 \pm 0.08) \cdot 10^{12} M_{\odot}$. For the groups with enough tracers close to the TS, the contribution of the Cosmological Constant makes the masses to be even higher. The results show the importance of including the local cosmic expansion in analyzing the Cosmic Flow of the local Universe.