Stellar populations of dwarf elliptical galaxies:: UBVRI photometry of dwarf elliptical galaxies in the Virgo Cluster

We present UBVRI surface photometry for 16 dwarf elliptical galaxies in the Virgo Cluster with previously measured kinematic properties. The global optical colors are red, with median values for the sample of 0.24 +/- 0.03 in U - B, 0.77 +/- 0.02 in B - V, and 1.02 +/- 0.03 in V - I. We recover the well-known color-magnitude relation for cluster galaxies but find no significant difference in dominant stellar population between rotating and nonrotating dwarf elliptical galaxies; the average age of the dominant stellar population is 5 - 7 Gyr in all 16 galaxies in this sample. Analysis of optical spectra confirm these age estimates and indicate Fe and Mg abundances in the range of 1/20 to one-third of solar, as expected for low-luminosity galaxies. Based on Lick indices and simple stellar population models, the derived [alpha/Fe] ratios are subsolar to solar, indicating a more gradual chemical enrichment history for dE's as compared with giant elliptical galaxies in the Virgo Cluster. These observations confirm the marked difference in stellar population and stellar distribution between dwarf and giant elliptical galaxies and further substantiate the need for alternative evolutionary scenarios for the lowest mass cluster galaxies. We argue that it is likely that several different physical mechanisms played a significant role in the production of the Virgo Cluster dE galaxies including in situ formation, infall of dE's that were once part of Local Group analogs, and transformation of dwarf irregular galaxies by the cluster environment. The observations support the hypothesis that a large fraction of the Virgo Cluster dE's are formed by ram pressure stripping of gas from infalling dI's.