Possible Subgroups of Globular Clusters and Planetary Nebulae in NGC 5128

TL;DR

This study identifies potential subgroups of globular clusters and planetary nebulae in NGC 5128, suggesting past dwarf galaxy accretion events through analysis of position and velocity data.

Contribution

It provides the first evidence of subgroups in NGC 5128's halo, indicating possible dwarf galaxy remnants and accretion history.

Findings

Detected 4 globular cluster subgroups beyond 10 arcmin radius.

Identified 4 planetary nebulae subgroups with typical dwarf galaxy parameters.

Some subgroups overlap with halo features and each other.

Abstract

We use recently compiled position and velocity data for the globular cluster and planetary nebula subsystems in NGC 5128, the nearby giant elliptical, to search for evidence of past dwarf-satellite accretion events. Beyond a 10 arcmin (~11 kpc) radius in galactocentric distance, we find tentative evidence for 4 subgroups of globular clusters and 4 subgroups of planetary nebulae. These each have > 4 members within a search radius of 2 arcmin and internal velocity dispersion of < 40 km/s, typical parameters for a dwarf galaxy. In addition, 2 of the globular cluster groupings overlap with 2 of the planetary nebulae groupings, and 2 subgroupings also appear to overlap with previously known arc and shell features in the halo light. Simulation tests of our procedure indicate that the probability of finding false groups due to chance is < 1%.