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

Abstract

Abstract We have carried out a search for substructure within the globular cluster (GC) systems of M84 (NGC 4374) and M86 (NGC 4406), two giant elliptical galaxies in the Virgo Cluster. We use wide-field (36′ × 36′), multicolor broadband imaging to identify GC candidates in these two galaxies, as well as several other nearby lower-mass galaxies. Our analysis of the spatial locations of the GC candidates reveals several substructures, including a peak in the projected number density of GCs 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 GC systems, and a boxy isodensity contour along the southeast side of the M86 GC system. We divide our sample into red (metal-rich) and blue (metal-poor) GC 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 GCs in the region and find that the bridge substructure is populated by GCs with a mix of velocities that are consistent with either M86 and M84, possibly providing further evidence for interaction signatures between the two galaxies.