Spatial Distribution of Globular Clusters in the Galaxy

TL;DR

This study investigates the spatial anisotropy of globular clusters in the Milky Way, revealing distinct structures at different distances and confirming known planar distributions with statistical significance.

Contribution

It provides a detailed analysis of globular cluster anisotropy using the inertia tensor and statistical tests, highlighting new structural insights at various galactic distances.

Findings

GCs at 2-10 kpc are coplanar with the Galactic plane

At large distances, GCs align with satellite galaxy structures

Old Halo GCs show polar and disk-like structures

Abstract

The Milky Way's satellite galaxies and Globular Clusters (GCs) are known to exhibit an anisotropic spatial distribution. We examine in detail this anisotropy by the means of the inertia tensor. We estimate the statistical significance of the results by repeating this analysis for random catalogues which use the radial distribution of the real sample. Our method reproduces the well-known planar structure in the distribution of the satellite galaxies. We show that for GCs several anisotropic structures are observed. The GCs at small distances, $2<R<10$ kpc, show a structure coplanar with the Galactic plane. At smaller and larger distances the whole sample of GCs shows quite weak anisotropy. Nevertheless, at largest distances the orientation of the structure is close to that of the satellite galaxies, i.e. perpendicular to the Galactic plane. We estimate the probability of random realization for this structure of 1.7%. The Bulge-Disk GCs show a clear disk-like structure lying within the galactic disk. The Old Halo GCs show two structures: a well pronounced polar elongated structure at $R<3$ kpc which is perpendicular to the galactic plane, and a less pronounced disk-like structure coplanar with the galactic disk at $6<R<20$ kpc. The Young Halo GCs do not show significant anisotropy.