The Ages of Passive Galaxies in a z = 1.62 Protocluster

• Main Authors: Lee-Brown, Donald B., Rudnick, Gregory H., Momcheva, Ivelina G., Papovich, Casey, Lotz, Jennifer M., Tran, Kim-Vy H., Henke, Brittany, Willmer, Christopher N. A., Brammer, Gabriel B., Brodwin, Mark, Dunlop, James, Farrah, Duncan
• Other Authors: Univ Arizona, Steward Observ
• Language: en
• Published: IOP PUBLISHING LTD 2017
• Subjects: galaxies: clusters: individual (CLG 0218.3-0510); galaxies: evolution; galaxies: high-redshift; galaxies: star formation
• Online Access: http://hdl.handle.net/10150/625163; http://arizona.openrepository.com/arizona/handle/10150/625163

We present a study of the relation between galaxy stellar age and mass for 14 members of the z = 1.62 protocluster IRC 0218, using multiband imaging and HST G102 and G141 grism spectroscopy. Using UVJ colors to separate galaxies into star-forming and quiescent populations, we find that, at stellar masses M*>= 10(10.85)M circle dot the quiescent fraction in the protocluster is f(Q) = 1.0(-0.37)(+0.00), consistent with a similar to 2x enhancement relative to the field value, f(Q) = 0.45(-0.03)(+0.03). At masses 10(10.2)M circle dot <= M* <= 10(10.85)M circle dot, f(Q) in the cluster is f(Q) = 0.40(-0.18)(+0.20), consistent with the field value of f(Q) = 0.28(-0.02)(+0.02). Using galaxy D-n(4000) values derived from the G102 spectroscopy, we find no relation between galaxy stellar age and mass. These results may reflect the impact of merger- driven mass redistribution-which is plausible, as this cluster is known to host many dry mergers. Alternately, they may imply that the trend in f(Q) in IRC 0218 was imprinted over a short timescale in the protocluster's assembly history. Comparing our results with those of other high- redshift studies and studies of clusters at z similar to 1, we determine that our observed relation between f(Q) and stellar mass only mildly evolves between z similar to 1.6 and z similar to 1, and only at stellar masses M* <= 10(10.85) M circle dot Both the z similar to 1 and z similar to 1.6 results are in agreement that the red sequence in dense environments was already populated at high redshift, z greater than or similar to 3, placing constraints on the mechanism(s) responsible for quenching in dense environments at z >= 1.5.