A Tale of two clusters

An analysis of gas-phase metallicity and nebular gas conditions in proto-cluster galaxies at z ∼ 2

Leo Y. Alcorn*, Anshu Gupta, Kim-Vy Tran, Glenn G. Kacprzak, Tiantian Yuan, Jonathan Cohn, Ben Forrest, Karl Glazebrook, Anishya Harshan, Lisa J. Kewley, Ivo Labbé, Themiya Nanayakkara, Casey Papovich, Lee R. Spitler, Caroline M. S. Straatman

*Corresponding author for this work

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The ZFIRE survey has spectroscopically confirmed two proto-clusters using the MOSFIRE instrument on Keck I: one at z = 2.095 in COSMOS and another at z = 1.62 in UKIRT Infrared Deep Sky Survey (UDS). Here, we use an updated ZFIRE data set to derive the properties of ionized gas regions of proto-cluster galaxies by extracting fluxes from emission lines Hβ 4861 Å, [O III] 5007 Å, Hα 6563 Å, [N II] 6585 Å, and [S II] 6716,6731 Å. We measure gas-phase metallicity of members in both proto-clusters using two indicators, including a strong-line indicator relatively independent of the ionization parameter and electron density. Proto-cluster and field galaxies in both UDS and COSMOS lie on the same Mass-Metallicity Relation with both metallicity indicators. We compare our results to recent Illustris TNG results, which report no significant gas-phase metallicity offset between protocluster and field galaxies until z = 1.5. This is in agreement with our observed metallicities, where no offset is measured between proto-cluster and field populations. We measure tentative evidence from stacked spectra that indicate UDS high-mass proto-cluster and field galaxies have differing [O III]/Hβ. ratios; however, these results are dependent on the sample size of the high-mass stacks.

Original languageEnglish
Article number153
Pages (from-to)1-11
Number of pages11
JournalAstrophysical Journal
Issue number2
Publication statusPublished - 1 Oct 2019

Bibliographical note

Copyright 2019 The American Astronomical Society. First published in the Astrophysical Journal, 883(2), 153, 2019, published by IOP Publishing. The original publication is available at http://www.doi.org/10.3847/1538-4357/ab3b0c. Version archived for private and non-commercial use with the permission of the author/s and according to publisher conditions. For further rights please contact the publisher.


  • galaxies: clusters: general
  • galaxies: evolution
  • galaxies: high-redshift
  • galaxies: Clusters: General
  • galaxies: Evolution
  • galaxies: High-redshift

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