In-situ vs accreted Milky Way globular clusters: a new classification method and implications for cluster formation
arXiv:2309.15902
Abstract
We present a new scheme for the classification of the in-situ and accreted globular clusters (GCs). The scheme uses total energy and -component of the orbital angular momentum and is calibrated using [Al/Fe] abundance ratio. We demonstrate that such classification results in the GC populations with distinct spatial, kinematic, and chemical abundance distributions. The in-situ GCs are distributed within the central 10 kpc of the Galaxy in a flattened configuration aligned with the MW disc, while the accreted GCs have a wide distribution of distances and a spatial distribution close to spherical. In-situ and accreted GCs have different distributions with the well-known bimodality present only in the metallicity distribution of the in-situ GCs. Furthermore, the accreted and in-situ GCs are well separated in the plane of abundance ratios and follow distinct sequences in the age-- plane. The in-situ GCs in our classification show a clear disc spin-up signature -- the increase of median at metallicities similar to the spin-up in the in-situ field stars. This signature signals the MW's disc formation, which occurred Gyrs ago (or at ) according to GC ages. In-situ GCs with metallicities of were thus born in the Milky Way disc, while lower metallicity in-situ GCs were born during early, turbulent, pre-disc stages of the evolution of the Galaxy and are part of its Aurora stellar component.
Submitted to MNRAS. Comments - in particular on the individual globular clusters you think we have misclassified - are welcome!