Kinematic Properties and Stellar Populations of Faint Early-Type Galaxies. II. Line-Strength Measurements of Central Coma Galaxies

We present line-strength measurements for 74 early-type galaxies in the core of the Coma cluster reaching down to velocity dispersions, sigma , of 30 km s-1. The index- sigma relations for our sample, including galaxies with sigma < 100 km s-1 (low- sigma ), differ in shape depending on which index is used. We note two types of relations for the metallic indices: one showing a break in the slope around ~100 km s-1 and another group with strong linear relations between an index and log sigma . We find no connection between the behavior of index- sigma relations with either alpha - or Fe-peak elements. However, we find indications that the relations are tighter for indices which do not depend on the microturbulent velocities of stellar atmospheres. We confirm previous results that low- sigma galaxies including dE/dS0s are on average younger, less metal rich, and have lower [ alpha /Fe] in comparison with E/S0s. Our data show that these trends derived for high- sigma galaxies extend down to dE/dS0s. This is a factor of ~2 lower in sigma than previously published work. We confirm that the observed anticorrelation between age and metallicity for high- sigma galaxies is consistent with the effects of correlated errors. Low- sigma galaxies also show a similar relation between age and metallicity as a result of correlated errors. However, they are offset from this relationship so that, on average, they are less metal rich and younger than their high- sigma counterparts.