Understanding the Origin and Dynamical Evolution of the Unique Open Star Cluster Berkeley 20 using FIRE Simulations

TL;DR

This study uses FIRE-2 galaxy simulations to analyze the origin and evolution of Berkeley 20-like open clusters, revealing key dynamical processes such as migration and satellite interactions that shape their current properties.

Contribution

The paper introduces a detailed simulation-based analysis of an OC analog to Berkeley 20, highlighting the importance of migration and satellite interactions in its evolution.

Findings

Simulated OC reaches similar galactic height as Berkeley 20.

Migration and satellite interactions significantly alter OC orbits.

OC shows resilience to disruption during dynamical events.

Abstract

Open clusters (OCs) act as key probes that can be leveraged to constrain the formation and evolution of the Milky Way (MW)'s disk, as each has a unique chemical fingerprint and well-constrained age. Significant Galactic dynamic interactions can leave imprints on the orbital properties of OCs, allowing us to use the present day properties of long-lived OCs to reconstruct the MW's dynamic history. To explore these changes, we identify OC analogs in FIRE-2 simulations of MW-mass galaxies. For this work, we focus on one particular FIRE-2 OC, which we identify as an analog to the old, subsolar, distant, and high Galactic latitude MW OC, Berkeley 20. Our simulated OC resides ~6 kpc from the galactic center and ultimately reaches a height $|Z_{\mathrm{max}}|>2$ kpc from the galactic disk, similar to Berkeley 20. We trace the simulated cluster's orbital and environmental history, identifying key perturbative episodes, including: (1) an interaction with a gas overdensity in a spiral arm that prompts an outward migration event and (2) a substantial interaction with a Sagittarius Dwarf Spheroidal Galaxy-mass satellite that causes significant orbital modification. Our simulated OC shows significant resilience to disruption during both its outward migration and the satellite-driven heating event that causes subsequent inward migration. Ultimately, we find these two key processes -- migration and satellite heating -- are essential to include when assessing OC orbital dynamics in the era of Gaia.