Kinematic Properties and Stellar Populations of Faint Early-Type Galaxies. I. Velocity Dispersion Measurements of Central Coma Galaxies

We present velocity dispersion measurements for 69 faint early-type galaxies in the core of the Coma cluster, spanning -22.0<M_R<-17.5 mag. We examine the L-\sigma relation for our sample and compare it to that of bright ellipticals from the literature. The distribution of the the faint early-type galaxies in the L-sigma plane follows the relation L ~ \sigma^{2.01\pm0.36}, which is significantly shallower from L ~ \sigma^4 as defined for the bright ellipticals. While increased rotational support for fainter early-type galaxies could account for some of the difference in slope, we show that it cannot explain it. We also investigate the Colour-\sigma relation for our Coma galaxies. Using the scatter in this relation, we constrain the range of galaxy ages as a function of their formation epoch for different formation scenarios. Assuming a strong coordination in the formation epoch of faint early-type systems in Coma, we find that most had to be formed at least 6 Gyrs ago and over a short 1 Gyr period.