Mild Velocity Dispersion Evolution of massive galaxies since z

Making use of public spectra from Cimatti et al. (2008), we measure for the first time the velocity dispersion of spheroid-like massive (M* ~ 10X1Mq) galaxies at 2 ~ 1.6. By comparing with galaxies of similar stellar mass at lower redshifts, we find evidence for a mild evolution in velocity dispersion, decreasing from ~240kms~1 at 2 ~ 1.6 down to ~ 180kms_1 at 2 ~ 0. Such mild evolution contrasts with the strong change in size (a factor of ~ 4) found for these type of objects in the same cosmic time, and it is consistent with a progressive larger role, at lower redshift, of the dark matter halo in setting the velocity dispersion of these galaxies. We discuss the implications of our results within the context of different scenarios proposed for the evolution of these massive objects.