Dynamical segregation of galaxies into groups and clusters


E-mail: mlares@oac.uncor.edu


We have performed a systematic analysis of the dynamics of different galaxy populations in galaxy groups from the 2dFGRS. For this purpose we have combined all the groups into a single system, where velocity v and radius r are expressed non-dimensionally. We have used several methods to compare the distributions of relative velocities of galaxies with respect to the group centre for samples selected according to their spectral type Madgwick et al., bj band luminosity and BR colour index. We have found strong segregation effects: spectral type I objects show a statistically narrower velocity distribution than that of galaxies with a substantial star formation activity (types II–IV). Similarly, the same behaviour is observed for galaxies with colour index BR > 1 compared to galaxies with BR < 1. Bright (Mb < −19) and faint (Mb > −19) galaxies show the same segregation. It is not important once the sample is restricted to a given spectral type. These effects are particularly important in the central region (Rp < 0.5Rvir) and do not have a strong dependence on the mass of the parent group. These trends show a strong correlation between the dynamics of galaxies in groups and star formation rate reflected both by spectral type and by colour index.