Timing Mass of the Local Group

TL;DR

This paper examines how new observations and theoretical insights influence the estimated mass and dynamics of the Local Group, highlighting discrepancies with previous estimates and potential for future research.

Contribution

It analyzes the impact of recent measurements and cosmological factors on the timing mass of the Local Group, offering updated estimates and discussing implications for dark matter and cosmology.

Findings

Timing mass of the LG is approximately 5 x 10^12 solar masses.

Recent data increases the estimated mass compared to previous models.

Discrepancies exist between timing mass and other mass estimators.

Abstract

The classic model of the Local Group (LG) is that of two dominant constituents, the Milky Way and M31, first separating and then detaching from the Hubble flow, leading to a nearly radial approaching orbit. This simple model has been confronted by new measurements of the 3D M31 kinematics, by cosmological simulations, and by theoretical understanding of the impact of massive substructures such as the Large Magellanic Cloud. This article explores the consequences of new observations and theory on the determination of the mass and dynamics of the LG. The M31 tangential velocity measurement and contribution from the cosmological constant both increase the implied timing mass of the LG to be $\sim 5 \times 10^{12}$ M$_\odot$. Timing mass estimates for the LG tend to be larger than the sum of the Milky Way and M31 halo masses, and larger than independent LG mass estimators. Precision future kinematics have the potential to explore the origin of this difference, shed light on dark matter in the LG, the origin of its angular momentum, and possibly even local values of cosmological parameters.