No globular cluster progenitors in Milky Way satellite galaxies

TL;DR

This study uses orbit integrations and a new binding criterion to investigate the origins of Milky Way globular clusters, finding no clear associations with classical dwarf satellites, implying they may have come from disrupted galaxies or had dark matter halos.

Contribution

The paper introduces a novel orbit-based method and binding criterion to assess globular cluster associations with satellite galaxies, providing new insights into their origins.

Findings

No clear associations between globular clusters and classical dwarf galaxies.

Globular clusters likely originated from disrupted satellites or had dark matter halos.

The method successfully recovers known associations like Sagittarius dwarf.

Abstract

In order to find the possible progenitors of Milky Way globular clusters, we perform orbit integrations to track the orbits of 170 Galactic globular clusters and the eleven classical Milky Way satellite galaxies backwards in time for 11 Gyr in a Milky-Way-plus-satellites potential including the response of the MW to the infall of the Large Magellanic Cloud and the effect of dynamical friction on the satellites. To evaluate possible past associations, we devise a globular-cluster--satellite binding criterion based on the satellite's tidal radius and escape velocity and we test it on globular clusters associated with the Sagittarius dwarf and on dwarf galaxies associated with the Large Magellanic Cloud. For these, we successfully recover the dynamical associations highlighted by previous studies and we derive their time of accretion by the Galaxy by using Gaia EDR3 data. Assuming that Milky Way globular clusters are and have been free of dark matter and thus consist of stars alone, we demonstrate that none of the globular clusters show any clear association with the eight classical dwarf spheroidal galaxies even though a large fraction of them are believed to be accreted. This means that accreted globular clusters either came in as part of now-disrupted satellite galaxies or that globular clusters may have had dark matter halos in the past -- as suggested by the similar metallicity between globular clusters and dwarf galaxies.