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. The Astrophysical Journal, 910 (1). ISSN 0004-637X

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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 $\rm H\alpha$ emitting sources, chosen from the HiZELS narrow-band survey, with metallicities derived from $\rm N2\ (\frac{\rm [NII] \lambda 6584}{\rm H \alpha})$ line ratio. For the mass-matched samples of protocluster and field galaxies, we find that protocluster galaxies with $10^{9.9} \rm M_\odot \leq M_* \leq 10^{10.9} \rm M_\odot$ are metal deficient by $0.10 \pm 0.04$ dex ($2.5\sigma$ significance) compared to their coeval field galaxies. This metal deficiency is absent for low mass galaxies, $\rm M_* <10^{9.9} \rm M_\odot$. Moreover, relying on both SED-derived and $\rm {H\alpha}$ (corrected for dust extinction based on $\rm {M_*}$) SFRs, we find no strong environmental dependence of SFR-$\rm {M_*}$ 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 $2.5\sigma$ 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 ($z \gtrsim 2$). 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 which are more prevalent in dense environments.

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Journal Article
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The Astrophysical Journal
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This is an author-created, un-copyedited version of an article accepted for publication/published in The Astrophysical Journal. IOP Publishing Ltd is not responsible for any errors or omissions in this version of the manuscript or any version derived from it. The Version of Record is available online at doi: 10.3847/1538-4357/abe5a3.
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15 Feb 2021 14:10
Last Modified:
10 Apr 2021 01:36