SEGREGATIONS IN CLUSTERS OF GALAXIES

We analyse a sample of about 2000 galaxies in 40 regular clusters, to look for evidence of segregation with respect to galaxy luminosities a nd morphological types. We find evidence of luminosity segregation for galaxies brighter than M-R < -21.5, i.e. typically the four brightest members of each cluster. We also find evidence of morphological cal s egregation: both the core-radius and the velocity dispersion increase along the Hubble sequence (ellipticals - S0 - early spirals - late spi rals). Galaxies of different types have different velocity dispersion profiles, being steeper for later type galaxies. Simple modelling allo ws us to show that elliptical (and, to a lesser extent, S0) orbits are mostly tangential in the cluster core, and nearly isotropic outside, while spiral (in particular late-spiral) orbits are predominantly radi al. A viable interpretation of our results is that (1) late spirals, a t variance with other type galaxies, are a non-virialized cluster popu lation, still on partially radial infalling orbits, (2) the elliptical phase-space distribution is evolving towards energy equipartition thr ough the process of dynamical friction, (3) S0 and early-spirals have intermediate distributions between these two extremes.