Co-Evolution of Galactic Nuclei and Globular Cluster Systems

TL;DR

This paper presents a model showing that inspiraling globular clusters can form dense galactic nuclei, matching observed properties, and potentially seed early black hole growth, explaining the formation of nuclear star clusters and quasars.

Contribution

It introduces a simple, observationally consistent model of globular cluster inspiral contributing to nuclear star cluster formation and early black hole seed development.

Findings

Globular clusters can form dense central structures similar to observed NSCs.

The NSC mass fraction scales with galaxy stellar mass as M_NSC/M_* = 0.0025 M_{*,11}^{-0.5}.

Disrupted globular clusters may provide most of the mass for NSCs in galaxies below 10^{11} Msun.

Abstract

We revisit the hypothesis that dense galactic nuclei are formed from inspiraling globular clusters. Recent advances in understanding of the continuous formation of globular clusters over cosmic time and the concurrent evolution of the galaxy stellar distribution allow us to construct a simple model that matches the observed spatial and mass distributions of clusters in the Galaxy and the giant elliptical galaxy M87. In order to compare with observations, we model the effects of dynamical friction and dynamical evolution, including stellar mass loss, tidal stripping of stars, and tidal disruption of clusters by the growing galactic nucleus. We find that inspiraling globular clusters form a dense central structure, with mass and radius comparable to the typical values in observed nuclear star clusters (NSCs) in late-type and low-mass early-type galaxies. The density contrast associated with the NSC is less pronounced in giant elliptical galaxies. Our results indicate that the NSC mass as a fraction of mass of the galaxy stellar spheroid scales as M_NSC/M_* = 0.0025 M_{*,11}^{-0.5}. Thus disrupted globular clusters could contribute most of the mass of NSCs in galaxies with stellar mass below 10^{11} Msun. The inner part of the accumulated cluster may seed the growth of a central black hole via stellar dynamical core collapse, thereby relieving the problem of how to form luminous quasars at high redshift. The seed black hole may reach about 10^5 Msun within 1 Gyr of the beginning of globular cluster formation.