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^{2.01pm0.36}, 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.
Download