Globular clusters as indicators of Galactic evolution

TL;DR

This study analyzes the origins and distribution of globular clusters in the Milky Way, revealing isotropic distributions in streams, bimodal age-metallicity relations, and the spatial orientation of satellite galaxies relative to the Galaxy and supergalactic plane.

Contribution

It provides new insights into the spatial distribution, origin, and environmental influences on globular clusters using Gaia data and analysis of large-scale structures.

Findings

GCs in streams are isotropic in distribution.

Bimodal age-metallicity relation distinguishes clusters from streams and disk.

Satellite galaxy planes are perpendicular to the Galactic disk and supergalactic plane.

Abstract

We have studied the system of globular clusters (GCs) that formed in other galaxies and eventually accreted onto the Milky Way. Thus, the samples of GCs belonging to different tidal streams, obtained on the basis of the latest data from the Gaia observatory, were taken from the literature. We measured the anisotropy of the distribution of these GCs using the gyration tensor and found that the distribution of GCs in the streams is isotropic. Nevertheless, it can be seen that some of the accreted GCs included into existing samples actually belong to the disk of the Galaxy. To clarify the origin of GCs, we investigated the ``age--metallicity'' relation. This dependence demonstrates bimodality and its two different branches clearly show the difference between the clusters formed in the streams and in the disk of the Galaxy. Furthermore, we have studied the influence of the large--scale environment of the Galaxy (i.e., the Local Supercluster) on the distribution of satellite galaxies and Galactic GCs. The satellite galaxies of the Milky Way are known to form an anisotropic planar structure, so we included them in our analysis too. An inspection has shown that the plane of the satellite galaxies is perpendicular both to the disk of the Galaxy and the supergalactic plane. For GCs more distant than 100~Kpc, a similar picture is observed.