Intra and Inter-Cluster Metallicity Dispersion in FIRE Open Clusters

Star clusters are thought to be the essential building blocks of the Milky Way’s Galactic disk; “strong chemical tagging” – the premise that all star clusters can be reconstructed given age, kinematic, and chemistry information alone – is a driving force behind many current and upcoming large Galactic spectroscopic surveys (e.g., GALAH, WEAVE). However, despite their significance, robust theoretical connections between open cluster (OC) properties and the larger Galactic environment remain substantially unexplored. In this work, we characterize abundance patterns in OCs in the Latte suite of FIRE-2 galaxy simulations — specifically to investigate if strong chemical tagging is possible. We select ~400 open clusters from the last 100 Myr of one Latte simulation, m12i, with minimum resolved star cluster mass of ~10^4.6 M_ⵙ, and calculate the intra and inter-cluster abundance scatter in these clusters. We compare these results with analogous calculations drawn from observations of OCs in the Milky Way from APOGEE. We find the intra-cluster scatter of the data and simulation to be comparable. While the abundance scatter in each cluster is minimal, the mean abundance patterns of different clusters are not unique. Using clusters as overall tags of formation, we measure the radial [Fe/H] gradient across the disk and find the inner slope to be shallow, ~-0.025 dex/kpc, as opposed to ~-0.068 dex/kpc as measured from APOGEE open clusters in the Milky Way. Finally, we demonstrate how the sampling of clusters affects a two-component fit to the radial metallicity gradient.