Universal depletion of metal-poor globular clusters in inner galaxy regions: Fossil record of black hole retention

TL;DR

This study reveals a universal triangular depletion of metal-poor globular clusters in galaxy centers, linked to black hole retention and galaxy mass, providing insights into galaxy assembly and cluster dynamics.

Contribution

It uncovers a universal depleted region in globular cluster systems and links its morphology to black hole retention and galaxy mass, offering a new perspective on galaxy evolution.

Findings

Depleted regions are larger in more massive galaxies.

Black hole retention influences globular cluster dissolution.

Depletion pattern correlates with galaxy mass and assembly history.

Abstract

We analyzed the spatial distribution of globular cluster (GC) systems across 37 host galaxies in a two dimensional parameter space defined by projected galactocentric distance Rg and metallicity Fe/H. We identified a universal triangular depleted region characterized by a lack of metal poor GCs in the inner parts of host galaxies. The morphology of this depleted region correlates with the luminous mass of the host galaxies; more massive galaxies consistently exhibit more extended depleted regions. We attribute this phenomenon to the combined influence of large scale galactic assembly and internal GC dynamics, particularly the initial retention of black holes within GCs. Metal poor GCs contain a more massive and compact black hole subsystem, which drives more energetic few body encounters and injects greater kinetic energy into the stellar population. This extra energy, combined with strong tidal forces in central galactic regions, accelerates the dissolution of low metallicity GCs, producing the triangular depleted pattern in the Rg - Fe/H space. Stronger tidal fields in more massive galaxies confine surviving metal poor GCs to larger radii, broadening the depleted region. The morphology of this region may serve as a potential distance indicator for host galaxies. Our results also suggest that scenarios with substantial black hole natal kicks are unlikely, as too few retained black holes would erase the metallicity dependent cluster dissolution required to form the observed depletion region.