The Colors of Dwarf Elliptical Galaxy Globular Cluster Systems , Nuclei and Stellar Halos

We present the results of a Hubble Space Telescope WFPC2 F555W and F814W survey of 69 dwarf elliptical galaxies (dEs) in the Virgo and Fornax Clusters and Leo Group. The V − I colors of the dE globular clusters, nuclei, and underlying field star populations are used to trace the dE star-formation histories. We find that the dE globular cluster candidates are as blue as the metal-poor globular clusters of the Milky Way. The observed correlation of the dE globular cluster systems’ V − I color with the luminosity of the host dE is strong evidence that the globular clusters were formed within the the halos of dEs and do not have a pre-galactic origin. Assuming the majority of dE clusters are old, the mean globular cluster colorhost galaxy luminosity correlation implies a cluster metallicity − galaxy luminosity relation of 〈ZGC〉 ∝ L 0.22±0.05 B , which is significantly shallower than the field star metallicity host galaxy luminosity relationship observed in Local Group dwarfs (〈ZFS〉 ∝ L ). The dE stellar envelopes are 0.1 − 0.2 magnitudes redder in V − I than their globular clusters and nuclei. This color offset implies separate star-formation episodes within the dEs for the clusters and field stars, while the very blue colors of two dE nuclei trace a third star-formation event in those dEs less than a Gyr ago. Subject headings: galaxies: dwarfs —galaxies: nuclei — galaxies: star clusters — galaxies: stellar content — galaxies: evolution — clusters: individual(Virgo, Fornax, Leo) Department of Astronomy and Astrophysics, University of California, Santa Cruz, CA 95064; [email protected] Gemini Observatory, Casilla 603, La Serena, Chile; [email protected] Space Telescope Science Institute, Baltimore, MD 21218; [email protected]