Abstract
Abstract Nuclear stellar clusters are common in the center of galaxies. We consider the possibility that their progenitors assumed to be globular clusters may have formed elsewhere, migrated to, and assembled near their present location. The main challenge for this scenario is whether globular clusters can withstand the tidal field of their host galaxies. Our analysis suggests that provided the mass-density distribution of background potential is relatively shallow, as in some galaxies with relatively flat surface brightness profiles, the tidal field near the center of galaxies may be shown to be able to compress rather than disrupt a globular cluster at a distance from the center much smaller than the conventionally defined “tidal disruption radius” r t . To do so, we adopt a previously constructed formalism and consider the secular evolution of star clusters with a homogeneous mass-density distribution. We analytically solve the secular equations in the limit that the mass density of stars in the galactic center approaches a uniform distribution. Our model indicates that a star cluster could travel to distances much smaller than r t without disruption, thus potentially contributing to the formation of the nuclear cluster. However, appropriate numerical N-body simulations are needed to confirm our analytic findings.
Highlights
GAIA data reveal the prevalence of stellar streams in the Galaxy (Myeong et al 2018, 2019; Helmi et al 2018; Koppelman et al 2018; Deason et al 2018; Necib et al 2019)
Based on the above formalism, we examine the condition under which the tidal perturbation from the galactic potential is compressive
It has long been assumed that tidal perturbation on satellites by an external gravitational field is disruptive
Summary
GAIA data reveal the prevalence of stellar streams in the Galaxy (Myeong et al 2018, 2019; Helmi et al 2018; Koppelman et al 2018; Deason et al 2018; Necib et al 2019). If the merger tree is the pathway for galactic assembly, nuclear clusters and central massive black holes would coagulate together with the host building block galaxies(Pfeffer et al 2014) After their orbits are virialized, relatively massive entities may undergo further orbital decay due to the effect of dynamical friction(Tremaine 1976b; Just et al 2011; Neumayer et al 2020). The nearby Fornax dwarf spheroidal galaxy (dSph) hosts six globular clusters (Wang et al 2019) and their orbital decay time scale, due to dynamical friction, has been estimated to be less than 1 Gyr (Hernandez & Gilmore 1998) These clusters remain in the field of Fornax due to the tidal stirring by the Galactic halo potential(Oh et al 2000).
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