On the Survival of High-Altitude Open Clusters within the Milky Way Galaxy Tides

TL;DR

This study uses simulations to analyze how the vertical tidal field of the Milky Way affects the lifespan of high-altitude open clusters, revealing a complex relationship between altitude and cluster survival.

Contribution

It provides new insights into the impact of Galactic tidal forces on open cluster longevity, especially considering the role of vertical tidal shocks and Galactic structures.

Findings

Cluster lifespan decreases with increasing orbital altitude up to 600 pc.

Clusters near the Galactic plane have longer lifespans due to fewer vertical shocks.

Tidal effects from arms and the bar can double cluster survival times inside arms.

Abstract

It is a common assumption that high-altitude open clusters live longer compared with clusters moving close to the Galactic plane. This is because at high altitudes, open clusters are far from the disruptive effects of in-plane substructures, such as spiral arms, molecular clouds and the bar. However, an important aspect to consider in this scenario is that orbits of high-altitude open clusters will eventually cross the Galactic plane, where the vertical tidal field of the disk is strong. In this work we simulate the interaction of open clusters with the tidal field of a detailed Milky Way Galactic model at different average altitudes and galactocentric radii. We find that the life expectancy of clusters decreases as the maximum orbital altitude increases and reaches a minimum at altitudes of approximately 600 pc. Clusters near the Galactic plane live longer because they do not experience strong vertical tidal shocks from the Galactic disk; then, for orbital altitudes higher than 600 pc, clusters start again to live longer due to the decrease in the number of encounters with the disk. With our study, we find that the compressive nature of the tides in the arms region and the bar have an important role on the survival of small clusters by protecting them from disruption: clusters inside the arms can live up to twice as long as those outside the arms at similar galactocentric distance.