Stellar Populations of Dwarf Elliptical Galaxies:UBVRIPhotometry of Dwarf Elliptical Galaxies in the Virgo Cluster

We present UBVRI surface photometry for 16 dwarf elliptical galaxies in theVirgo Cluster with previously measured kinematic properties. The global opticalcolors 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 knowncolor-magnitude relation for cluster galaxies, but find no significantdifference in dominant stellar population between rotating and non-rotatingdwarf elliptical galaxies; the average age of the dominant stellar populationis 5-7 Gyr in all 16 galaxies in this sample. Analysis of optical spectraconfirm these age estimates and indicate Fe and Mg abundances in the range of1/20th to 1/3 of solar, as expected for low luminosity galaxies. Based on Lickindices and simple stellar population models, the derived [alpha/Fe] ratios aresub-solar to solar, indicating a more gradual chemical enrichment history fordEs as compared to giant elliptical galaxies in the Virgo Cluster. Theseobservations confirm the marked difference in stellar population and stellardistribution between dwarf and giant elliptical galaxies and furthersubstantiate the need for alternative evolutionary scenarios for the lowestmass cluster galaxies. We argue that it is likely that several differentphysical mechanisms played a significant role in the production of the Virgocluster dE galaxies including in situ formation, infall of dEs that were oncepart of Local Group analogs, and transformation of dwarf irregular galaxies bythe cluster environment. The observations support the hypothesis that a largefraction of the Virgo cluster dEs are formed by ram pressure stripping of gasfrom infalling dIs.Comment: 37 pages, 8 figures (2 color). Accepted to AJ (scheduled for Dec. 2004