Scl-dE1 GC1: An Extended Globular Cluster in a Low-Luminosity Dwarf Elliptical Galaxy

TL;DR

This paper reports the discovery of an unusually large extended globular cluster in a dwarf elliptical galaxy, suggesting the existence of two modes of globular cluster formation in such galaxies.

Contribution

First identification of an extended globular cluster in a low-luminosity dwarf elliptical galaxy, proposing two formation modes for globular clusters.

Findings

The cluster's half-light radius is ~22 pc, making it one of the largest known.

The cluster's stellar population matches that of its host galaxy.

Evidence suggests two distinct formation modes for globular clusters.

Abstract

We report the discovery from Hubble Space Telescope ACS images of an extended globular cluster, denoted by Scl-dE1 GC1, in the Sculptor Group dwarf Elliptical galaxy Scl-dE1 (Sc22). The distance of the dE is determined as 4.3 +/- 0.25 Mpc from the I magnitude of the tip of the red giant branch in the color-magnitude diagram. At this distance the half-light radius of Scl-dE1 GC1 is ~22 pc, placing it among the largest clusters known, particularly for globular clusters associated with dwarf galaxies. The absolute magnitude of Scl-dE1 GC1 is Mv = -6.7 and, to within the photometric uncertainties of the data, the cluster stellar population appears indistinguishable from that of the dE. We suggest that there may be two modes of globular cluster formation in dwarf galaxies, a "normal" mode with half-light radii of typically 3 pc, and an "extended" mode with half-light radii of ~10 pc or more.