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 color- host galaxy luminosity correlation implies a cluster metallicity - galaxy luminosity relation of Z₆₂ \ LB^0. 22 \ 0. 05, which is significantly shallower than the field star metallicity - host galaxy luminosity relationship observed in Local Group dwarfs (Z₅ₒ \ L^0. 4). 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.