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

26 Scopus citations


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 ≥ 1010.85 M, the quiescent fraction in the protocluster is fQ = 1.0-0.37 +0.00, consistent with a ∼ 2× enhancement relative to the field value, fQ = 0.45-0.03 +0.03. At masses 1010.2 M ≤ M ≤ 1010.85 M, fQ in the cluster is fQ = 0.40-0.18 +0.20, consistent with the field value of fQ = 0.28-0.02 +0.02. Using galaxy Dn (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 fQ 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 fQ and stellar mass only mildly evolves between z ∼ 1.6 and z ∼ 1, and only at stellar masses M ≤ 1010.85 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 ≥ 1.5.

Original languageEnglish (US)
Article number43
JournalAstrophysical Journal
Issue number1
StatePublished - Jul 20 2017


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

ASJC Scopus subject areas

  • Astronomy and Astrophysics
  • Space and Planetary Science


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