Colors of Dwarf Ellipticals from GALEX to WISE

Abstract

Multi-color photometry is presented for a sample of 60 dwarf ellipticals (dE) selected by morphology. The sample uses data from GALEX, SDSS and WISE to investigate the colors in filters NUV, ugri and W1 (3.4mum). We confirm the blueward shift in the color-magnitude relation for dwarf ellipticals, compared to CMR for bright ellipticals, as seen in previous studies. However, we find the deviation in color across the UV to near-IR for dE's is a strong signal of a younger age for dwarf ellipticals, one that indicates decreasing mean age with lower stellar mass. Lower mass dE's are found to have mean ages of 4 Gyrs and mean [Fe/H] values of -1.2. Age and metallicity increase to the most massive dE's with mean ages similar to normal ellipticals (12 Gyrs) and their lowest metallicities ([Fe/H] = -0.3). Deduced initial star formation rates for dE's, combined with their current metallicities and central stellar densities, suggests a connection between field LSB dwarfs and cluster dE's, where the cluster environment halts star formation for dE's triggering a separate evolutionary path.