The Global Dynamical Atlas of the Milky Way Mergers: Constraints from Gaia EDR3–
based Orbits of Globular Clusters, Stellar Streams, and Satellite Galaxies
Khyati Malhan1,9
, Rodrigo A. Ibata2
, Sanjib Sharma3,4
, Benoit Famaey2
, Michele Bellazzini5
,
Raymond G. Carlberg6
, Richard D’Souza7
, Zhen Yuan2
, Nicolas F. Martin1,2
, and Guillaume F. Thomas8
1 Max-Planck-Institut für Astronomie, Königstuhl 17, D-69117, Heidelberg, Germany; kmalhan07@gmail.com
2 Université de Strasbourg, CNRS, Observatoire astronomique de Strasbourg, UMR 7550, F-67000 Strasbourg, France
3 Sydney Institute for Astronomy, School of Physics, The University of Sydney, NSW 2006, Australia
4 ARC Centre of Excellence for All Sky Astrophysics in Three Dimensions (ASTRO-3D), Australia
5 INAF—Osservatorio di Astrofisica e Scienza dello Spazio, via Gobetti 93/3, I-40129 Bologna, Italy
6 Department of Astronomy & Astrophysics, University of Toronto, Toronto, ON M5S 3H4, Canada
7 Vatican Observatory, Specola Vaticana, V-00120, Vatican City State, Italy
8 Universidad de La Laguna, Dpto. Astrofísica E-38206 La Laguna, Tenerife, Spain
Received 2021 December 11; revised 2022 January 14; accepted 2022 January 18; published 2022 February 17
Abstract
The Milky Way halo was predominantly formed by the merging of numerous progenitor galaxies. However,
our knowledge of this process is still incomplete, especially in regard to the total number of mergers, their
global dynamical properties and their contribution to the stellar population of the Galactic halo. Here, we
uncover the Milky Way mergers by detecting groupings of globular clusters, stellar streams, and satellite
galaxies in action (J) space. While actions fully characterize the orbits, we additionally use the redundant
information on their energy (E) to enhance the contrast between the groupings. For this endeavor, we use Gaia
EDR3–based measurements of 170 globular clusters, 41 streams, and 46 satellites to derive their J and E. To
detect groups, we use the ENLINK software, coupled with a statistica