Tidal disruption of star clusters in galaxy formation simulations

TL;DR

This study uses cosmological simulations to analyze how tidal forces affect the evolution and survival of star clusters in Milky Way-like galaxies, revealing that early strong tidal disruption diminishes over time.

Contribution

It provides new insights into the temporal evolution of tidal fields acting on star clusters and compares the disruption of in situ and ex situ clusters in a cosmological context.

Findings

Tidal forces are strongest within the first few hundred Myr after cluster formation.

The median tidal eigenvalue decreases to about 3,000 Gyr$^{-2}$ after 1 Gyr.

Ex situ clusters tend to have higher bound fractions than in situ clusters of similar initial mass.

Abstract

We investigate the evolution of the tidal field experienced by massive star clusters using cosmological simulations of Milky Way-sized galaxies. Clusters in our simulations experience the strongest tidal force in the first few hundred Myr after formation, when the maximum eigenvalue of the tidal tensor reaches several times $10^4$ Gyr$^{-2}$. After about 1 Gyr the tidal field plateaus at a lower value, with the median $\lambda_{\rm m} \sim 3 \times 10^3$ Gyr$^{-2}$. The fraction of time clusters spend in high tidal strength ($\lambda_{\rm m} > 3 \times 10^4$ Gyr$^{-2}$) regions also decreases with their age from $\sim$20% immediately after formation to less than 1% after 1 Gyr. At early ages both the in situ and ex situ clusters experience similar tidal fields, while at older ages the in situ clusters in general experience stronger tidal field due to their lower orbits in host galaxy. This difference is reflected in the survival of clusters: we looked into cluster disruption calculated in simulation runtime and found that ex situ star clusters of the same initial mass typically end up with higher bound fraction at the last available simulation snapshot than the in situ ones.