Differences in the Structural Properties and Star-formation Rates of Field and Cluster Galaxies at z~1

Abstract

We investigate the dependence of galaxy sizes and star formation rates (SFRs) on their environment using a mass-limited sample of quiescent and star-forming galaxies with log(M _*/{M}_⊙ ) ≥ 9.5 at \bar{z}=0.92 selected from the NEWFIRM medium-band Survey (NMBS). Using the Galaxy Environment Evolution Collaboration 2 spectroscopic cluster catalog and the accurate photometric redshifts from the NMBS, we select quiescent and star-forming cluster (\bar{σ }=490 km s^-1) galaxies within two virial radius, R _vir, intervals of 2 > R _vir > 0.5 and R _vir < 0.5. Galaxies residing outside of the 2 R _vir of both the cluster centers and the additional candidate over-densities are defined as our field sample. Galaxy structural parameters are measured from the COSMOS legacy Hubble Space Telescope/ACS F814W image. The sizes and Sérsic indices of quiescent field and cluster galaxies have the same distribution regardless of R _vir. However, cluster star-forming galaxies within 0.5 R _vir have lower mass-normalized average sizes by 16+/- 7 % , and a higher fraction of Sérsic indices with n\gt 1, than field star-forming galaxies. The average SFRs of star-forming cluster galaxies show a trend of decreasing SFR with clustocentric radius. The mass-normalized average SFR of cluster star-forming galaxies is a factor of 2{--}2.5 (7{--}9σ ) lower than that of star-forming galaxies in the field. While we find no significant dependence on environment for quiescent galaxies, the properties of star-forming galaxies are affected, which could be the result of environment acting on their gas content.