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

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.