The Differential Size Growth of Field and Cluster Galaxies at z = 2.1 Using the ZFOURGE Survey

There is ongoing debate regarding the extent that environment affects galaxy size growth beyond z ≥ 1. To investigate the differences in star-forming and quiescent galaxy properties as a function of environment at z = 2.1, we create a mass-complete sample of 59 cluster galaxies and 478 field galaxies with log(M_*/{{M}_⊙ }) ≥ 9 using photometric redshifts from the ZFOURGE survey. We compare the mass-size relation of field and cluster galaxies using measured galaxy semi-major axis half-light radii ({{r}_1/2,maj}) from CANDELS Hubble Space Telescope (HST)/F160W imaging. We find consistent mass-normalized (log(M_*/{{M}_⊙ }) = 10.7) sizes for quiescent field galaxies ({{r}_1/2,maj}=1.81+/- 0.29 kpc) and quiescent cluster galaxies ({{r}_1/2,maj}=2.17+/- 0.63 kpc). The mass-normalized size of star-forming cluster galaxies ({{r}_1/2,maj}=4.00+/- 0.26 kpc) is 12% larger (Kolmogorov-Smirnov (KS) test 2.1σ ) than star-forming field galaxies ({{r}_1/2,maj}=3.57+/- 0.10 kpc). From the mass-color relation we find that quiescent field galaxies with 9.7 < log(M_*/{{M}_⊙ }) ≤slant 10.4 are slightly redder (KS test 3.6σ) than quiescent cluster galaxies, while cluster and field quiescent galaxies with log(M_*/{{M}_⊙ }) > 10.4 have consistent colors. We find that star-forming cluster galaxies are on average 20% redder than star-forming field galaxies at all masses. Furthermore, we stack galaxy images to measure average radial color profiles as a function of mass. Negative color gradients are only present for massive star-forming field and cluster galaxies with log(M_*/{{M}_⊙ }) \gt 10.4; the remaining galaxy masses and types have flat profiles. Our results suggest, given the observed differences in size and color of star-forming field and cluster galaxies, that the environment has begun to influence/accelerate their evolution. However, the lack of differences between field and cluster quiescent galaxies indicates that the environment has not begun to significantly influence their evolution at z ∼ 2.

This paper includes data gathered with the 6.5 m Magellan Telescopes located at Las Campanas Observatory, Chile.