The accretion history of the Milky Way. I. How it shapes globular clusters and dwarf galaxies

TL;DR

This study investigates how the Milky Way's accretion history influences the structural properties of globular clusters and dwarf galaxies, revealing correlations between their sizes, energies, and orbital parameters shaped by tidal interactions.

Contribution

It introduces a calibration method linking the orbital energy of halo objects to their accretion epoch, highlighting the role of MW tides and dynamical friction in shaping their structures.

Findings

Globular cluster sizes depend on orbital pericenter and energy.

Milky Way tides explain the correlation between cluster size and orbital parameters.

Earlier accreted satellites are smaller due to tidal effects.

Abstract

Halo inhabitants are individual stars, stellar streams, star and globular clusters, and dwarf galaxies. Here we compare the two last categories that include objects of similar stellar mass, which are often studied as self-dynamical equilibrium systems. We discover that the half-light radius of globular clusters depends on their orbital pericenter and total energy, and that Milky Way (MW) tides may explain the observed correlation. We also suggest that the accretion epoch of stellar systems in the MW halo can be calibrated by the total orbital energy, and that such a relation is due to both the mass growth of the MW and dynamical friction affecting mostly satellites with numerous orbits. This calibration starts from the bulge, to Kraken, Gaia Sausage Enceladus, Sagittarius stellar systems, and finally to the new coming dwarfs, either or not linked to the vast-polar structure. The most eccentric globular clusters and dwarfs have their half-light radius scaling as the inverse of their binding energy, and this over more than two decades. This means that earlier arriving satellites are smaller due to the tidal effects of the MW. Therefore, most halo inhabitants appear to have their structural parameters shaped by MW tides and also by ram-pressure for the most recent arrivals, the dwarf galaxies. The correlations found in this study can be used as tools to further investigate the origin of globular clusters and dwarfs, as well as the assembly history of our Galaxy.