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Evidence for Gas-phase Metal Deficiency in Massive Protocluster Galaxies at z ∼2.2

Sattari, Zahra and Mobasher, Bahram and Chartab, Nima and Darvish, Behnam and Shivaei, Irene and Scoville, Nick and Sobral, David (2021) Evidence for Gas-phase Metal Deficiency in Massive Protocluster Galaxies at z ∼2.2. Astrophysical Journal, 910 (1). Art. No. 57. ISSN 0004-637X. doi:10.3847/1538-4357/abe5a3.

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We study the mass–metallicity relation for 19 members of a spectroscopically confirmed protocluster in the COSMOS field at z = 2.2 (CC2.2), and compare it with that of 24 similarly selected field galaxies at the same redshift. Both samples are Hα emitting sources, chosen from the HiZELS narrowband survey, with metallicities derived from the N2 ([NII]λ6584/Hα) line ratio. For the mass-matched samples of protocluster and field galaxies, we find that protocluster galaxies with 10^(9.9) M⊙ ≤ M* ≤ 10^(10.9) M⊙ are metal deficient by 0.10 ± 0.04 dex (2.5σ significance) compared to their coeval field galaxies. This metal deficiency is absent for low-mass galaxies, M* < 10^(9.9) M⊙. Moreover, relying on both spectral energy distribution derived and Hα (corrected for dust extinction based on M*) star formation rates (SFRs), we find no strong environmental dependence of the SFR–M* relation; however, we are not able to rule out the existence of small dependence due to inherent uncertainties in both SFR estimators. The existence of 2.5σ significant metal deficiency for massive protocluster galaxies favors a model in which funneling of the primordial cold gas through filaments dilutes the metal content of protoclusters at high redshifts (z ≳ 2). At these redshifts, gas reservoirs in filaments are dense enough to cool down rapidly and fall into the potential well of the protocluster to lower the gas-phase metallicity of galaxies. Moreover, part of this metal deficiency could be originated from galaxy interactions that are more prevalent in dense environments.

Item Type:Article
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URLURL TypeDescription Paper ItemCode
Sattari, Zahra0000-0002-0364-1159
Chartab, Nima0000-0003-3691-937X
Darvish, Behnam0000-0003-4919-9017
Shivaei, Irene0000-0003-4702-7561
Scoville, Nick0000-0002-0438-3323
Sobral, David0000-0001-8823-4845
Additional Information:© 2021. The American Astronomical Society. Received 2020 October 31; revised 2021 January 10; accepted 2021 February 10; published 2021 March 25. We thank the anonymous referee for providing insightful comments and suggestions that improved the quality of this work. I.S. is supported by NASA through the NASA Hubble Fellowship grant #HST-HF2-51420, awarded by the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Inc., for NASA, under contract NAS5-26555. The authors wish to recognize and acknowledge the very significant cultural role and reverence that the summit of Maunakea has always had within the indigenous Hawaiian community. We are most fortunate to have the opportunity to conduct observations from this mountain. This research has been done during the COVID-19 global pandemic. The authors would like to thank all the essential workers who risked their lives allowing us to work from home safely. Based on data obtained at the W. M. Keck Observatory, which is operated as a scientific partnership among the California Institute of Technology, the University of California, and the National Aeronautics and Space Administration. The Observatory was made possible by the generous financial support of the W. M. Keck Foundation.
Group:Astronomy Department
Funding AgencyGrant Number
NASA Hubble FellowshipHST-HF2-51420
W. M. Keck FoundationUNSPECIFIED
Subject Keywords:Metallicity; Galaxy evolution; Protoclusters; High-redshift galaxy clusters; Large-scale structure of the universe
Issue or Number:1
Classification Code:Unified Astronomy Thesaurus concepts: Metallicity (1031); Galaxy evolution (594); Protoclusters (1297); Highredshift galaxy clusters (2007); Large-scale structure of the universe (902)
Record Number:CaltechAUTHORS:20210401-094809937
Persistent URL:
Official Citation:Zahra Sattari et al 2021 ApJ 910 57
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:108603
Deposited By: Tony Diaz
Deposited On:01 Apr 2021 18:22
Last Modified:01 Apr 2021 18:22

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