Globular Clusters As Tracers of Fine Structure in the Dramatic Shell Galaxy NGC 474

TL;DR

This study links globular clusters to visible stellar streams in galaxy NGC 474, revealing that many GCs are associated with fine structures, confirming their role as tracers of galaxy merger history.

Contribution

It provides direct observational evidence connecting globular clusters with merger-induced fine structures in a post-merger galaxy, highlighting their origin through minor mergers.

Findings

35% of GCs outside 3 effective radii are in fine structures

Strong spatial correlation between GCs and stellar streams (99.9% significance)

Blue GCs are predominantly associated with fine structures

Abstract

Globular clusters (GCs) are some of the most visible tracers of the merging and accretion history of galaxy halos. Metal-poor GCs, in particular, are thought to arrive in massive galaxies largely through dry, minor merging events, but it is rare to see a direct connection between GCs and visible stellar streams. NGC 474 is a post-merger early-type galaxy with dramatic fine structures made of concentric shells and radial streams that have been more clearly revealed by deep imaging. We present a study of GCs in NGC 474 to better establish the relationship between merger-induced fine structure and the GC system. We find that many GCs are superimposed on visible streams and shells, and about 35% of GCs outside $3R_{\rm e,galaxy}$ are located in regions of fine structure. The spatial correlation between the GCs and fine structure is significant at the 99.9% level, showing that this correlation is not coincidental. The colors of the GCs on the fine structures are mostly blue, and we also find an intermediate-color population that is dominant in the central region, and which will likely passively evolve to have colors consistent with a traditional metal-rich GC population. The association of the blue GCs with fine structures is direct confirmation that many metal-poor GCs are accreted onto massive galaxy halos through merging events, and that progenitors of these mergers are sub-L* galaxies.