The ACS Virgo Cluster Survey. XVII. The Spatial Alignment of Globular Cluster Systems With Early-Type Host Galaxies

TL;DR

This study examines the spatial alignment of globular clusters with their host early-type galaxies, revealing that both metal-rich and metal-poor GCs tend to align with the galaxy's major axis, implying anisotropic halo formation and merging.

Contribution

It provides new observational evidence that globular clusters, including metal-poor ones, align with galaxy major axes, supporting theories of anisotropic halo assembly and merger history.

Findings

Red GCs strongly align with galaxy major axes.

Blue GCs also show alignment, indicating early formation.

Alignment suggests anisotropic halo assembly and merging.

Abstract

We study the azimuthal distribution of globular clusters (GCs) in early-type galaxies and compare them to their host galaxies using data from the ACS Virgo Cluster Survey. We find that in host galaxies with visible elongation (epsilon > 0.2) and intermediate to high luminosities (M_z<-19), the GCs are preferentially aligned along the major axis of the stellar light. The red (metal-rich) GC subpopulations show strong alignment with the major axis of the host galaxy, which supports the notion that these GCs are associated with metal-rich field stars. The metal-rich GCs in lenticular galaxies show signs of being more strongly associated with disks rather than bulges. Surprisingly, we find that the blue (metal-poor) GCs can also show the same correlation. If the metal-poor GCs are part of the early formation of the halo and built up through mergers, then our results support a picture where halo formation and merging occur anisotropically, and where the present day major axis is an indicator of the preferred merging axis.