The Ages of Passive Galaxies in a z = 1.62 Protocluster

Donald B. Lee-Brown, Gregory H. Rudnick, Ivelina G. Momcheva, Casey Papovich, Jennifer M. Lotz, Kim-Vy H. Tran, Brittany Henke, Christopher N. A. Willmer, Gabriel B. Brammer, Mark Brodwin, James Dunlop, Duncan Farrah

Research output: Contribution to journalArticlepeer-review

Abstract / Description of output

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}* ≥slant {10}10.85 {M}⊙ , the quiescent fraction in the protocluster is {f}Q={1.0}-0.37+0.00, consistent with a ˜ 2× enhancement relative to the field value, {f}Q={0.45}-0.03+0.03. At masses {10}10.2 {M}⊙ ≤slant {M}* ≤slant {10}10.85 {M}⊙ , 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˜ 1, we determine that our observed relation between f Q and stellar mass only mildly evolves between z˜ 1.6 and z˜ 1, and only at stellar masses {M}* ≤slant {10}10.85 {M}⊙ . Both the z˜ 1 and z˜ 1.6 results are in agreement that the red sequence in dense environments was already populated at high redshift, z≳ 3, placing constraints on the mechanism(s) responsible for quenching in dense environments at z≥slant 1.5.
Original languageEnglish
Number of pages17
JournalAstrophysical Journal
Issue number1
Publication statusPublished - 20 Jul 2017

Keywords / Materials (for Non-textual outputs)

  • galaxies: clusters: individual: CLG 0218.3-0510
  • galaxies: evolution
  • galaxies: high-redshift
  • galaxies: star formation


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