Tidal disruption of star clusters in galaxy formation simulations

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(m) similar to 3 x 10(3) Gyr(-2). The fraction of time clusters spend in high tidal strength (lambda(m) > 3 x 10(4) Gyr(-2)) regions also decreases with their age from similar to 20 per cent immediately after formation to less than 1 per cent 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.

Automated summary

We investigated the evolution of tidal fields experienced by massive star clusters in Milky Way-sized galaxies using cosmological simulations. We found that the tidal force on clusters is strongest in the first few hundred million years after formation, after which it plateaus at a lower value. The fraction of time spent by clusters in high tidal strength regions decreases with age. In situ and ex situ clusters experience similar tidal fields at early ages, but in situ clusters generally experience stronger tidal fields at older ages due to their lower orbits. This difference in tidal fields affects the survival of clusters, with ex situ clusters typically having a higher bound fraction than in situ clusters.