Spectroscopy of early-type galaxies in A262

By calibrating dark matter densities to cosmological simulations we find assembly redshifts of z_DM_{approx}1-3, as previously reported for the Coma Cluster. The dynamical mass that follows the light is larger than expected for a Kroupa stellar initial mass function (IMF), especially in galaxies with high velocity dispersion {sigma}_eff_ inside the effective radius r_eff_. This could indicate a "massive" IMF in massive galaxies.

Alternatively, some of the dark matter in massive galaxies could follow the light very closely. In combination with our comparison sample of Coma early-type galaxies, we now have 5 of 24 galaxies where (1) mass follows light to 1-3r_eff_, (2) the dynamical mass-to-light ratio of all the mass that follows the light is large ({approx}8-10 in the Kron-Cousins R band), and (3) the dark matter fraction is negligible to 1-3r_eff_.

Unless the IMF in these galaxies is particularly "massive" and somehow coupled to the dark matter content, there seems to be a significant degeneracy between luminous and dark matter in at least some early-type galaxies. The role of violent relaxation is briefly discussed.