Rutgers University Astrophysics Seminar

Refreshments to follow in room 332W. ABSTRACT: We compare star formation histories of dwarf early-type galaxies (dwarf elliptical,dE, and dwarf lenticular galaxies,dS0) in two regions of different density in the Coma cluster. We measure the Lick/IDS line strength indices for ~70 dE/dS0 galaxies in the core of the Coma cluster and a region just outside the core which is believed to be infalling into the cluster. We derive ages, metallicities and abundance ratios for these galaxies, as well as relations between the Lick/IDS index and velocity dispersion. We find that majority of metallicity-dependent indices show no linear relations with velocity dispersion. Surprisingly, we find an unusually high fraction of dE/dS0 galaxies with supersolar alpha-ratios, mostly found in the infall region of the cluster. This implies short time scales for star formation histories for dE/dS0 galaxies and is comparable to more massive ellipticals. The range in age and metallicity for dE/dS0s with high alpha-ratios implies multiple formation scenarios for these galaxies, where some have experienced their short star formation bursts more recently.