2014A&A...567A..94S

We studied the size-surface brightness and the size-mass relations of a sample of 16 cluster elliptical galaxies in the mass range ∼10¹⁰-2x10¹¹M_☉, which were morphologically selected in the cluster RDCS J0848+4453 at z=1.27. Our aim is to assess whether they have completed their mass growth at their redshift or significant mass, and/or size growth can or must still take place until z=0. This will enable us to know whether the elliptical galaxies of clusters follow or not the observed size evolution of passive galaxies. To compare our data with the local universe we considered the Kormendy relation derived from the early-type galaxies of a local Coma Cluster reference sample and the WINGS survey sample. The comparison with the local Kormendy relation shows that the luminosity evolution due to the aging of the stellar content already assembled at z=1.27 brings them on the local relation. Moreover, this stellar content places them on the size-mass relation of the local cluster ellipticals. These results imply that for a given mass, the stellar mass at z∼1.3 is distributed within these ellipticals according to the same stellar mass profile of local ellipticals. We find that a pure size evolution, even mild, is ruled out for our galaxies since it would lead them away from both the Kormendy and the size-mass relation. If an evolution of the effective radius takes place, this must be compensated by an increase in the luminosity, hence of the stellar mass of the galaxies, to keep them on the local relations. We show that to follow the Kormendy relation, the stellar mass must increase as the effective radius. However, this mass growth is not sufficient to keep the galaxies on the size-mass relation for the same variation in effective radius. Thus, if we want to preserve the Kormendy relation, we fail to satisfy the size-mass relation and vice versa. The combined analysis of the size-surface brightness relation with the size-mass relation leads to the result that these galaxies cannot increase solely in size and cannot significantly grow in mass. We conclude that these 16 cluster ellipticals at z=1.27 have, for the most part, completed their stellar mass growth at the redshift they are and that consequently, their evolution at z<1.27 will be dominated by the aging of their stellar content. If this result is generalizable, then it shows that elliptical galaxies in the above mass range do not contribute to the observed size evolution of passive galaxies, as also found by other authors. This evolution would be instead mainly driven by disk galaxies. We do not find hints of differences between the properties of these cluster ellipticals and those of field ellipticals at comparable redshift, even if this last comparison is still based on a low number statistics.