Volume 630, October 2019
|Number of page(s)||8|
|Section||Letters to the Editor|
|Published online||23 September 2019|
Letter to the Editor
Origin of the system of globular clusters in the Milky Way
Kapteyn Astronomical Institute, University of Groningen, 9747 AD Groningen, The Netherlands
2 Dipartimento di Fisica e Astronomia, Università degli Studi di Bologna, Via Gobetti 93/2, 40129 Bologna, Italy
3 INAF – Osservatorio di Astrofisica e Scienza dello Spazio di Bologna, Via Gobetti 93/3, 40129 Bologna, Italy
Accepted: 9 September 2019
Context. The assembly history experienced by the Milky Way is currently being unveiled thanks to the data provided by the Gaia mission. It is likely that the globular cluster system of our Galaxy has followed a similarly intricate formation path.
Aims. To constrain this formation path, we explore the link between the globular clusters and the known merging events that the Milky Way has experienced.
Methods. To this end, we combined the kinematic information provided by Gaia for almost all Galactic clusters, with the largest sample of cluster ages available after carefully correcting for systematic errors. To identify clusters with a common origin we analysed their dynamical properties, particularly in the space of integrals of motion.
Results. We find that about 40% of the clusters likely formed in situ. A similarly large fraction, 35%, appear to be possibly associated to known merger events, in particular to Gaia-Enceladus (19%), the Sagittarius dwarf galaxy (5%), the progenitor of the Helmi streams (6%), and to the Sequoia galaxy (5%), although some uncertainty remains due to the degree of overlap in their dynamical characteristics. Of the remaining clusters, 16% are tentatively associated to a group with high binding energy, while the rest are all on loosely bound orbits and likely have a more heterogeneous origin. The resulting age–metallicity relations are remarkably tight and differ in their detailed properties depending on the progenitor, providing further confidence on the associations made.
Conclusions. We provide a table listing the likely associations. Improved kinematic data by future Gaia data releases and especially a larger, systematic error-free sample of cluster ages would help to further solidify our conclusions.
Key words: globular clusters: general / Galaxy: kinematics and dynamics / galaxies: dwarf / Galaxy: formation / Galaxy: evolution
© ESO 2019
Current usage metrics show cumulative count of Article Views (full-text article views including HTML views, PDF and ePub downloads, according to the available data) and Abstracts Views on Vision4Press platform.
Data correspond to usage on the plateform after 2015. The current usage metrics is available 48-96 hours after online publication and is updated daily on week days.
Initial download of the metrics may take a while.