Substructure in the Globular Cluster Populations of the Virgo Cluster Elliptical Galaxies M84 and M86

TL;DR

This study investigates substructures in the globular cluster systems of M84 and M86 in the Virgo Cluster, revealing spatial features and potential interactions between the galaxies through imaging and velocity data.

Contribution

It provides the first detailed analysis of globular cluster substructures in M84 and M86, highlighting interactions and spatial distributions of different metallicity populations.

Findings

Identified multiple substructures, including a density peak and a connecting bridge.

Blue (metal-poor) clusters dominate the identified substructures.

Velocity data suggest interactions between M84 and M86 globular clusters.

Abstract

We have carried out a search for substructure within the globular cluster systems of M84 (NGC 4374) and M86 (NGC 4406), two giant elliptical galaxies in the Virgo Cluster. We use wide-field (36 arcmin x 36 arcmin), multi-color broadband imaging to identify globular cluster candidates in these two galaxies as well as several other nearby lower-mass galaxies. Our analysis of the spatial locations of the globular cluster candidates reveals several substructures, including: a peak in the projected number density of globular clusters in M86 that is offset from the system center and may be at least partly due to the presence of the dwarf elliptical galaxy NGC 4406B; a bridge that connects the M84 and M86 globular cluster systems; and a boxy iso-density contour along the southeast side of the M86 globular cluster system. We divide our sample into red (metal-rich) and blue (metal-poor) globular cluster candidates to look for differences in the spatial distributions of the two populations and find that the blue cluster candidates are the dominant population in each of the substructures we identify. We also incorporate the measurements from two radial velocity surveys of the globular clusters in the region and find that the bridge substructure is populated by globular clusters with a mix of velocities that are consistent with either M86 and M84, possibly providing further evidence for interaction signatures between the two galaxies.