Tidal disruption of stellar clusters and their remnants' spatial distribution near the galactic center

TL;DR

This study uses N-body simulations to explore how galactic tidal forces disrupt stellar clusters near galactic centers, revealing conditions under which clusters survive or disintegrate, and explaining observed stellar populations.

Contribution

It provides a new criterion based on galactic density profiles for predicting cluster disruption, supported by simulations and applied to the Galactic Center.

Findings

Clusters are compressed or disrupted depending on the host galaxy's density profile.

Disrupted clusters can explain the presence of multiple stellar populations near SMBHs.

The criterion enhances understanding of cluster survival in galactic nuclei.

Abstract

The accretion of massive star clusters via dynamical friction has previously been established to be a likely scenario for the build up of nuclear stellar clusters (NSCs). A remaining issue is whether strong external tidal perturbation may lead to the severe disruption of loosely-bound clusters well before they sink deeply into the center of their host galaxies. We carry out a series of $N$-body simulations and verify our early idealized analytic models. We show if the density profile of the host galaxies can be described by a power-law distribution with an index, $\alpha <1$, the cluster would be compressed in the radial direction by the external galactic tidal field. In contrast, the galactic tidal perturbation is disruptive in regions with a steep, $\alpha >1$, density fall-off or in the very center where gravity is dominated by the point-mass potential of super-massive black holes (SMBHs). This sufficient criterion supplements the conventional necessary Roche-lobe-filling condition in determining the preservation versus disintegration of satellite stellar systems. We simulate the disruption of stellar clusters which venture on nearly-circular, modestly- or highly-eccentric orbits into the center of galaxies with a range of background density profiles and SMBHs. We obtain the spatial distribution of the stellar-cluster remnants. We apply these results to the NSC within a few parsecs from SMBH Sgr A$^\ast$ at the Galactic Center. Recent observations indicate the coexistence of two populations of stars with distinctively separate ages and metallicities. We verify that the subsolar-metalicity population can be the debris of disrupted stellar clusters.