Ages of S0 and Elliptical Galaxies in the Coma Cluster

The ages of stellar populations in 52 elliptical and S0 galaxies in the Coma Cluster are investigated, using a new spectroscopic sample. More than 40% of the S0's are found to have undergone star formation in their central regions during the last ~5 Gyr, while such activity is absent in the ellipticals. Galaxies in this sample have absolute magnitudes in the range -20.5 < MB < -17.5, and the fraction of S0 galaxies with recent star formation is higher at fainter luminosities. The observed luminosity range of S0 galaxies with signs of recent star formation activity is consistent with them being the descendants of typical star-forming spirals at intermediate redshift whose star formation has been halted as a consequence of the dense environment.