Weighing the Local Group in the Presence of Dark Energy

TL;DR

This paper revises the mass estimate of the Local Group by incorporating Dark Energy into the Timing Argument, resulting in a higher mass estimate and better alignment with cosmological simulations.

Contribution

It introduces a modified Timing Argument that accounts for Dark Energy, providing a more accurate mass estimate of the Local Group.

Findings

Local Group mass estimate increases by 13% with Dark Energy inclusion.

Scatter in mass ratio from simulations is approximately 0.16.

Calibrated virial mass of the Local Group is about 4.92 x 10^{12} solar masses.

Abstract

We revise the mass estimate of the Local Group (LG) when Dark Energy (in the form of the Cosmological Constant) is incorporated into the Timing Argument (TA) mass estimator for the Local Group (LG). Assuming the age of the Universe and the Cosmological Constant according to the recent values from the Planck CMB experiment, we find the mass of the LG to be M_TAL = (4.73 +- 1.03) x 10^{12} M_sun, which is 13% higher than the classical TA mass estimate. This partly explains the discrepancy between earlier results from LCDM simulations and the classical TA. When a similar analysis is performed on 16 LG-like galaxy pairs from the CLUES simulations, we find that the scatter in the ratio of the virial to the TA estimated mass is given by M_vir/M_TAL = 1.04 +-0.16. Applying it to the LG mass estimation we find a calibrated M_vir = (4.92 +- 1.08 (obs) +- 0.79 (sys)) x 10^{12} M_sun.