COSMOS field proto-cluster at z =2.08 (Spitler et al.2012, Yuan et al.2014) overlaid on 3D HST RGB image (F160W, F606W,F814W).

Galaxy clusters are the most over-dense environments in the universe and are an extreme laboratory for studying the physical processes that govern cosmological mass assembly, galaxy formation and evolution. With the growing number of known galaxy clusters at z~2, it is now possible to track how baryons cycle between stars, winds, and the ISM when cluster galaxies are still forming a large fraction of their stars. ZFIRE is the first comprehensive study to target hundreds of individual cluster galaxies at this pivotal epoch.

ZFIRE is obtaining the optical and near-IR spectroscopy needed to study a meaningful sample (>30 members) in each cluster, i.e. similar in size to cluster studies at lower redshifts. The deep near-IR spectroscopy is needed to robustly measure stellar populations and scaling relations for cluster galaxies as they transition from intensely star-forming systems to the passive galaxies that dominate local clusters. By combining the ZFIRE observations with legacy data-sets, we (i) measure cluster velocity dispersion and map the large scale structure; (ii) confirm quiescent and active members; and (iii) study physical properties of individual members that include gas-phase metallicities, star formation rates, and gas kinematics.