Radial Distribution Of ISM Gas-phase Metallicity In CLASH Clusters at
  z~0.35: A New Outlook On Environmental Impact On Galaxy Evolution
  We present the first observation of cluster-scale radial metallicity
gradients from star-forming galaxies. We use the DEIMOS spectrograph on the
Keck II telescope to observe two CLASH clusters at z~0.35: MACS1115+0129 and
RXJ1532+3021. Based on our measured interstellar medium (ISM) properties of
star-forming galaxies out to a radius of 2.5 Mpc from the cluster centre, we
find that the galaxy metallicity decreases as a function of projected
cluster-centric distance (-0.15+/-0.08 dex/Mpc) in MACS1115+01. On the
mass-metallicity relation (MZR), star-forming galaxies in MACS1115+01 are
offset to higher metallicity (~0.2 dex) than the local SDSS galaxies at a fixed
mass range. In contrast, the MZR of RXJ1532+30 is consistent with the local
comparison sample. RXJ1532+30 exhibits a bimodal radial metallicity
distribution, with one branch showing a similar negative gradient as
MACS1115+01 (-0.14+/-0.05 dex/Mpc) and the other branch showing a positive
radial gradient. The positive gradient branch in RXJ1532+30 is likely caused by
either interloper galaxies or an in-plane merger, indicating that cluster-scale
abundance gradients probe cluster substructures and thus the dynamical state of
a cluster. Most strikingly, we discover that neither the radial metallicity
gradient nor the offset from the MZR is driven by the stellar mass. We compare
our observations with Rhapsody-G cosmological hydrodynamical zoom-in
simulations of relaxed galaxy clusters and find that the simulated galaxy
cluster also exhibits a negative abundance gradient, albeit with a shallower
slope (-0.04+/-0.03 dex/Mpc). Our observations suggest that the negative radial
gradient originates from ram-pressure stripping and/or strangulation processes
in the cluster environments.
