2009ApJ...691.1862M

We present line-strength measurements for 74 early-type galaxies in the core of the Coma cluster reaching down to velocity dispersions, σ, of 30 km/s. The index-σ relations for our sample, including galaxies with σ < 100 km/s (low-σ), 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 and another group with strong linear relations between an index and log σ. We find no connection between the behavior of index-σ relations with either α- 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-σ galaxies including dE/dS0s are on average younger, less metal rich, and have lower [α/Fe] in comparison with E/S0s. Our data show that these trends derived for high-σ galaxies extend down to dE/dS0s. This is a factor of ∼2 lower in σ than previously published work. We confirm that the observed anticorrelation between age and metallicity for high-σ galaxies is consistent with the effects of correlated errors. Low-σ 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-σ counterparts.