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.
