2012ApJ...745..130R

We present the Kormendy and mass-size relations (MSR) for early-type galaxies (ETGs) as a function of environment at z ∼ 1.3. Our sample includes 76 visually classified ETGs with masses 10¹⁰ < M/M_☉< 10^11.5, selected in the Lynx supercluster and in the Great Observatories Origins Deep Survey/Chandra Deep Field South field; 31 ETGs in clusters, 18 in groups, and 27 in the field, all with multi-wavelength photometry and Hubble Space Telescope/Advanced Camera for Surveys observations. The Kormendy relation, in place at z ∼ 1.3, does not depend on the environment. The MSR reveals that ETGs overall appear to be more compact in denser environments: cluster ETGs have sizes on average around 30%-50% smaller than those of the local universe and a distribution with a smaller scatter, whereas field ETGs show an MSR with a similar distribution to the local one. Our results imply that (1) the MSR in the field did not evolve overall from z ∼ 1.3 to present; this is interesting and in contrast to the trend found at higher masses from previous works; (2) in denser environments, either ETGs have increased in size by 30%-50% on average and spread their distributions, or more ETGs have been formed within the dense environment from non-ETG progenitors, or larger galaxies have been accreted to a pristine compact population to reproduce the MSR observed in the local universe. Our results are driven by galaxies with masses M ≲ 2x10¹¹ M_☉ and those with masses M ∼ 10¹¹ M_☉ follow the same trends as that of the entire sample. Following the Valentinuzzi et al. definition of superdense ETGs, ∼35%-45% of our cluster sample is made up of superdense ETGs.