The cosmic epoch dependence of environmental effects on size evolution of red-sequence early-type galaxies

Abstract

[abridged] This work aims to observationally investigate the history of size growth of early-type galaxies and how the growth depends on cosmic epoch and the mass of the halo in which they are embedded. We carried out a photometric and structural analysis in the rest-frame $V$ band of a mass-selected ($\log M/M_\odot >10.7$) sample of red-sequence early-type galaxies with spectroscopic/grism redshift in the general field up to $z=2$ to complement a previous work presenting an identical analysis but in halos 100 times more massive and 1000 times denser. We homogeneously derived sizes (effective radii) fully accounting for the multi-component nature of galaxies and the common presence of isophote twists and ellipticity gradients. By using these mass-selected samples, composed of 170 red-sequence early-type galaxies in the general field and 224 identically selected and analyzed in clusters, we isolate the effect on galaxy sizes of the halo in which galaxies are embedded and its dependence on epoch. We find that the $\log$ of the galaxy size at a fixed stellar mass, $\log M/M_\odot= 11$, has increased with epoch at a rate twice as fast in the field than in cluster in the last 10 Gyr ($0.26\pm0.03$ versus $0.13\pm0.02$ dex per unit redshift). Red-sequence early-type galaxies in the general field reached the size of their cousins in denser environment by $z=0.25\pm0.13$ in spite of being three times smaller at $z\sim2$. Data point toward a model where size growth is epoch-independent (i.e., $\partial \log r_e /\partial z = c$), but with a rate $c$ depending on environment, $\partial c /\partial \log M_{halo} \approx 0.05$. Environment determines the growth rate ($d \log r_e / dz$) at all redshifts, indicating an external origin for the galaxy growth without any clear epoch where it ceases to have an effect.