Evolution of the Stellar Mass--Metallicity Relation - I: Galaxies in the z~0.4 Cluster Cl0024.

We present the stellar mass-stellar metallicity relationship (MZR) in the Cl0024+1654 galaxy cluster at z~0.4 using full spectrum stellar population synthesis modeling of individual quiescent galaxies. The lower limit of our stellar mass range is $M_*=10^{9.7}M_\odot$, the lowest galaxy mass at which individual stellar metallicity has been measured beyond the local universe. We report a detection of an evolution of the stellar MZR with observed redshift at $0.037\pm0.007$ dex per Gyr, consistent with the predictions from hydrodynamical simulations. Additionally, we find that the evolution of the stellar MZR with observed redshift can be explained by an evolution of the stellar MZR with their formation time, i.e., when the single stellar population (SSP)-equivalent ages of galaxies are taken into account. This behavior is consistent with stars forming out of gas that also has an MZR with a normalization that decreases with redshift. Lastly, we find that over the observed mass range, the MZR can be described by a linear function with a shallow slope, ($[Fe/H] \propto (0.16 \pm 0.03) \log M_*$). The slope suggests that galaxy feedback, in terms of mass-loading factor, might be mass-independent over the observed mass and redshift range.