Dynamics of the Local Group: the Outer Galactic Globular Star Clusters

TL;DR

This paper presents a model that fits the distances, redshifts, and proper motions of outer galactic globular clusters, revealing their complex orbital histories and potential first-time approaches to the Milky Way.

Contribution

It extends a previous model of the Local Group to successfully fit globular cluster data, offering insights into their orbital dynamics and origins.

Findings

Outer globular clusters have completed multiple orbits around the Milky Way.

Some clusters are approaching the Milky Way for the first time.

The model accommodates various observed proper motions and tidal tail orientations.

Abstract

A model for the mass in and around the Local Group previously used to fit redshifts of dwarf galaxies to their distances between 50 kpc and 2.6 Mpc under the condition of small and growing primeval departures from homogeneity is shown to allow fits to distances and redshifts of twelve galactic globular clusters at galactocentric distances greater than 30 kpc. The solutions also fit three sets of measured globular cluster proper motions and the orientation of one observation of tidal tails. In some solutions these outer globular clusters have circled the Milky Way several times, losing information about their initial conditions. In other trajectories globular clusters are approaching the Milky Way for the first time from formation in mass concentrations modest enough to have small internal velocities and initially moving away from the proto--Milky Way galaxy at close to the general rate of expansion of the universe.