Newly-Discovered Globular Clusters in NGC 147 and NGC 185 from PAndAS

TL;DR

This study reports the discovery of four new globular clusters in NGC 147 and NGC 185 using PAndAS data, providing insights into their properties, metallicities, and spatial distribution beyond the galaxies' main bodies.

Contribution

The paper presents the first homogeneous optical and near-IR photometry of these clusters, confirming their association with the dwarf galaxies and analyzing their metallicities and ages.

Findings

Four new globular clusters discovered beyond galaxy boundaries.

Clusters are predominantly metal-poor with [Fe/H] < -1.25 dex.

GC specific frequencies are consistent with similar dwarf ellipticals.

Abstract

Using data from the Pan-Andromeda Archaeological Survey (PAndAS), we have discovered four new globular clusters (GCs) associated with the M31 dwarf elliptical (dE) satellites NGC 147 and NGC 185. Three of these are associated with NGC 147 and one with NGC 185. All lie beyond the main optical boundaries of the galaxies and are the most remote clusters yet known in these systems. Radial velocities derived from low resolution spectra are used to argue that the GCs are bound to the dwarfs and are not part of the M31 halo population. Combining PAndAS with UKIRT/WFCAM data, we present the first homogeneous optical and near-IR photometry for the entire GC systems of these dEs. Colour-colour plots and published colour-metallicity relations are employed to constrain GC ages and metallicities. It is demonstrated that the clusters are in general metal poor ([Fe/H] < -1.25 dex), while the ages are more difficult to constrain. The mean (V-I)$_0$ colours of the two GC systems are very similar to those of the GC systems of dEs in the Virgo and Fornax clusters, as well as the extended halo GC population in M31. The new clusters bring the GC specific frequency (S_N) to ~9 in NGC 147 and ~5 in NGC 185, consistent with values found for dEs of similar luminosity residing in a range of environments.