Oral Presentation
Enhanced gas-phase metallicities and suppressed outflows indicated for galaxies in a core region of the cosmic noon cluster
Presenter: Kota Adachi (Tohoku University)
Chemical evolution of galaxies is determined by not only past star formation activities but also gas inflow from surrounding large-scale structures and outflow from galaxies back to the halos driven by AGN or SNe. Such gaseous processes may well depend on the surrounding environments, especially in clusters, because of inefficient gas accretion and enhanced gas stripping. Past simulations predict that the vigorous mass assembly and transition of gas accretion phase occurs at cosmic noon. However, the details of how the gas flows actually work are still under debate, and it is also hard to observationally quantify them.
In this presentation, we report on our near-infrared spectroscopy of member galaxies in cluster XCS2215 (z=1.46) with Keck/MOSFIRE to measure gas-phase metallicities of 27 Hα emitters. Our results show that the cluster galaxies have 0.13-0.17 dex higher metallicities for the same stellar mass compared to field galaxies in COSMOS at similar redshift. We also see an environmental offset in the fundamental metallicity relation which indicates that the metallicity offset is not due to the difference in evolutionary stages of gas mass and SFR, but is due to environmental effects. Compared with other clusters at higher redshifts (z>2), the z=1.5 cluster galaxies are more metal-rich due to chemical evolution. Moreover, low-mass galaxies show larger evolution than massive galaxies, which is consistent with the downsizing scenario.
We also indirectly estimate the outflow rates by combining the gas mass derived by ALMA observations and gaseous metallicity of this work, and compare them with chemical evolution models including outflows. As a result, we find that galaxies in XCS2215 core are consistent with weaker outflow than that of field counterparts.
All these results put together, we conclude that the metallicity enhancement in this X-ray cluster is caused by the lack of metallicity dilution due to inefficient gas accretion in shock- heated hot ICM. Moreover, the outflow is also suppressed due to confinement of metal- enriched gas by dense IGM in the cluster core, leading to further chemical evolution by recycling the gas.
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