Keck Spectroscopy of Globular Clusters in the Virgo Cluster Dwarf Elliptical Galaxy VCC 1386

Abstract

We present the results of a Keck spectroscopic study of globular clusters associated with the Virgo Cluster dwarf elliptical galaxy (dE) VCC 1386. We analyze blue spectroscopic absorption lines from 3500 to 5500 Å for 13 globular cluster candidates and confirm that five are associated with VCC 1386. By comparing metal and Balmer line indices of these globular clusters with α-enhanced single stellar population models, we find that these systems are metal poor, with [Fe/H]>-1.35, and old, with ages >5 Gyr at 3 σ confidence, placing their formation at z>~1. This is one of the first spectroscopic studies of globular clusters surrounding dEs in a cluster, revealing that some low-mass galaxies in rich environments form at least part of their stellar mass early in the history of the universe. We further find that the luminosity-weighted stellar population of VCC 1386 itself is younger and more metal rich than its globular clusters, consistent with (V-I)₀ colors from Hubble Space Telescope imaging. This implies that VCC 1386, like the Local Group dEs, has had multiple episodes of star formation. Globular clusters associated with low-luminosity systems, however, appear to be roughly as old as those associated with giant galaxies, contrary to the ``downsizing'' formation of their bulk stellar populations.