Low-luminosity early-type galaxies in the Coma Cluster: Variations in spectral properties

We present spectra of nine low-luminosity early-type galaxies (M-B > -17.5) in the Coma Cluster. The spectra, which were obtained with the Multiple Mirror Telescope and cover the spectral region 3300-5350 Angstrom exhibit a large variation in Balmer line strengths. In fact, the line-strength variation among the Coma low-luminosity galaxies is as large as that found among a sample of low-luminosity elliptical galaxies in the Virgo Cluster and lower density environments. When compared with detailed population synthesis models, the variation in Balmer line strengths among the Coma galaxies indicates a range in luminosity-weighted mean age from similar to 1 to similar to 12 Gyr. The two youngest galaxies are shown to be in a poststarburst state, i.e., they are not simply former spirals whose star formation was recently terminated. Moreover, the similar to 1 Gyr ages of these two youngest low-luminosity galaxies are similar to those of the brighter poststarburst galaxies in the Coma Cluster.