Identifying the possible ex-situ origin of the globular clusters of the Milky Way: A kinematic study

TL;DR

This study uses simulations to identify potential globular clusters in the Milky Way that originated from dwarf satellite galaxies, revealing new associations and orbital characteristics that support an ex-situ origin hypothesis.

Contribution

It introduces a comprehensive kinematic analysis linking Milky Way globular clusters to their possible dwarf galaxy progenitors using advanced simulations.

Findings

29 GCs potentially originated from dwarf satellites

First-time associations with Large Magellanic Cloud and Sagittarius

Predicted unique orbital signatures for Sagittarius GCs

Abstract

This is the second paper in a series, which studies the likelihood that some globular clusters (GCs) of the Milky Way (MW) could have originated from a dwarf satellite galaxy (DSG). Using a large suite of three-body simulations we determine the present-day orbital properties of 154 GCs that could have escaped from 41 MW DSGs over the past $8\,\mathrm{Gyrs}$. For the MW we considered two sets of static and dynamic models which account for the sustained growth of the MW since its birth. We focus on the Magellanic Clouds and Sagittarius. We compare the apogalactic distance, eccentricity, and orbital inclination of the MW GCs with those of runaway GCs from DSGs, to constrain their possible ex-situ origin. We observe a positive correlation between a DSG mass and the dispersion of its runaway GCs in the orbital parameter space of ($R_\mathrm{ap}$, $e$). We provide tables of the identified MW GCs and their likely associated progenitors. In total, we find 29 (19%) MW GCs which could be kinematically associated with MW DSGs. We report, for the first time, 6 and 10 new associations with the Large Magellanic Cloud and the Sagittarius, respectively. For the Sagittarius we predict a concentration of runaway GCs at large apogalactic distances of $R_\mathrm{ap}\approx275-375\,\mathrm{kpc}$, $e\approx0.8$, and a relative inclination of $\Delta\theta\approx20^{\circ}$. So far, there has not been any observed GCs with such orbital elements. Complemented with photometric and spectroscopic observations, and cosmological simulations, the findings from the present study could conclusively settle the debate over the in-situ vs. ex-situ origin of the MW GCs.