Enhanced Gas-phase Metallicities and Suppressed Outflows for Galaxies in a Rich Cluster Core at Cosmic Noon

Abstract We present the results of near-infrared spectroscopy using Keck/MOSFIRE for 23 member galaxies in the X-ray cluster XCS 2215 ( z = 1.46) to investigate the environmental dependence of gaseous flows and metallicities. We find that the metallicities derived from H α and [N II ] emission lines of the cluster galaxies are enhanced by 0.08–0.15 dex with ∼2 σ significance compared to field counterparts for the same stellar mass. This suggests that inefficient gas accretion in the shock-heated intracluster medium (ICM) in the cluster core results in the lack of metallicity dilution. We also estimate the mass-loading factor by comparing the observed galaxies with the chemical evolution model that takes into account the outflow processes on the metallicity-versus-gas mass fraction diagram constructed together with the Atacama Large Millimeter/submillimeter Array data. We find that the outflows from galaxies in the cluster core region tend to be weaker than those of galaxies in the general field. It is likely due to the confinement of gas by the high pressure of the surrounding ICM in the cluster core, which leads to the recycling of the outflowing gas that comes back to the system and is used for further star formation, resulting in the progression of chemical evolution. Compared with higher-redshift protocluster galaxies at z > 2, which tend to show lower metallicity than the field galaxies due probably to dilution of metals by pristine gas inflow, we are seeing the transition of the gas accretion mode from the efficient cold stream mode to the inefficient hot mode.