Abstract
In order to assess whether the environment has a significant effect on galaxy sizes, we compare the mass--size relations of cluster and field galaxies in the $0.4 < z < 0.8$ redshift range from the ESO Distant Cluster Survey (EDisCS) using HST images. We analyse two mass-selected samples, one defined using photometric redshifts ($10.2 \le \log M_\ast/M_{\odot} \le 12.0$), and a smaller more robust subsample using spectroscopic redshifts ($10.6 \le \log M_\ast/M_{\odot} \le 11.8$). We find no significant difference in the size distributions of cluster and field galaxies of a given morphology. Similarly, we find no significant difference in the size distributions of cluster and field galaxies of similar rest-frame $B-V$ colours. We rule out average size differences larger than $10$--$20$\% in both cases. Consistent conclusions are found with the spectroscopic and photometric samples. These results have important consequences for the physical process(es) responsible for the size evolution of galaxies, and in particular the effect of the environment. The remarkable growth in galaxy size observed from $z\sim2.5$ has been reported to depend on the environment at higher redshifts ($z>1$), with early-type/passive galaxies in higher density environments growing earlier. Such dependence disappears at lower redshifts. Therefore, if the reported difference at higher-$z$ is real, the growth of field galaxies has caught up with that of cluster galaxies by $z\sim1$. Any putative mechanism responsible for galaxy growth has to account for the existence of environmental differences at high redshift and their absence (or weakening) at lower redshifts.
Highlights
It is well established that galaxies have shown remarkable evolution in their physical properties such as their sizes over cosmic time
We aim to examine the role of environment on the galaxy stellar mass–size relation in the 0.4 < z < 0.8 redshift range since this could be the transition epoch when the putative environmental differences found at higher redshifts cease to be present
Finding no significant differences in the galaxy size distributions in clusters and the field implies either that such differences do not exist or that, if they do, they are too small to be detected in our sample
Summary
It is well established that galaxies have shown remarkable evolution in their physical properties such as their sizes over cosmic time. Observations of present-day galaxies clearly show that their sizes are correlated with their stellar masses, and that this correlation evolves significantly over look-back time This size evolution was put forth by some of the first works published on this topic showing that massive quiescent galaxies at high redshift (z > 1) were much more compact than their local counterparts (Shen et al 2003; Daddi et al 2005; McIntosh et al 2005; Buitrago et al 2008; van Dokkum et al 2008). There is extensive evidence indicating that at z ∼ 0 the mass–size relation for galaxies with a given morphology does not depend significantly on environment either (Shen et al 2003; Maltby et al 2010; Rettura et al 2010; Poggianti et al 2013), some subtle differences may still be present (Cebrian & Trujillo 2014) This seems to suggest that there must be an epoch when the environment ceases to affect galaxy sizes, perhaps because the growth has already been completed in all environments.
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