A Blue Tilt in the Globular Cluster System of the Milky Way-like Galaxy NGC 5170

TL;DR

This study discovers a blue tilt in the metal-poor globular clusters of NGC 5170, indicating a mass-metallicity relation similar to that in elliptical galaxies, supported by HST imaging data.

Contribution

First detection of a blue tilt in a Milky Way-like galaxy's globular cluster system, extending the understanding of globular cluster properties beyond massive ellipticals.

Findings

Blue tilt detected at 3sigma significance in NGC 5170

Globular cluster system is richer than the Milky Way

Potential ultra-compact dwarf identified

Abstract

Here we present HST/ACS imaging, in the B and I bands, of the edge-on Sb/Sc galaxy NGC 5170. Excluding the central disk region region, we detect a 142 objects with colours and sizes typical of globular clusters (GCs). Our main result is the discovery of a `blue tilt' (a mass-metallicity relation), at the 3sigma level, in the metal-poor GC subpopulation of this Milky Way like galaxy. The tilt is consistent with that seen in massive elliptical galaxies and with the self enrichment model of Bailin & Harris. For a linear mass-metallicity relation, the tilt has the form Z ~ L^{0.42 +/- 0.13}. We derive a total GC system population of 600 +/- 100, making it much richer than the Milky Way. However when this number is normalised by the host galaxy luminosity or stellar mass it is similar to that of M31. Finally, we report the presence of a potential Ultra Compact Dwarf of size ~ 6 pc and luminosity M_I ~ -12.5, assuming it is physically associated with NGC 5170.