CLASH-VLT: Enhancement of (O/H) in z=0.35 RXJ 2248-4431 cluster galaxies
  (Abridged) We explore the Frontier Fields cluster RXJ2248-443 at z~0.35 with
VIMOS/VLT spectroscopy from CLASH-VLT, which covers a central region
corresponding to almost 2 virial radii. The fluxes of [OII], Hbeta, [OIII],
Halpha and [NII] emission lines were measured allowing the derivation of (O/H)
gas metallicities, star formation rates based on extinction-corrected Halpha
fluxes and active galactic nuclei (AGN) contamination. We compare our sample of
cluster galaxies to a population of field galaxies at similar redshifts. We use
the location of galaxies in projected phase-space to distinguish between
cluster and field galaxies. Both populations follow the star-forming-sequence
in the diagnostic diagrams, which allow disentangling between the ionising
sources in a galaxy, with only few galaxies classified as Seyfert II. Both
field and cluster galaxies follow the "Main-Sequence" of star forming galaxies,
with no substantial difference observed between the two populations. In the
Mass - Metallicity (MZ) plane, both high mass field and cluster galaxies show
comparable (O/H)s to the local SDSS MZ relation, with an offset of low mass
galaxies towards higher metallicities. While both the metallicities of
"accreted" (R < R500) and "infalling" (R > R500) cluster members are comparable
at all masses, the cluster galaxies from the intermediate, mass complete bin
show more enhanced metallicities than their field counterparts. The
intermediate mass field galaxies are in accordance with the expected (O/H)s
from the Fundamental Metallicity relation, while the cluster members deviate
strongly from the model predictions. The results of this work are in accordance
with studies of other clusters at z < 0.5 and favour the scenario in which the
hot halo gas of log(M/Msun)<10.2 cluster galaxies is removed due to mild ram
pressure stripping, leading to an increase in their gas-phase metallicity.
