CLASH-VLT: Strangulation of cluster galaxies in MACSJ0416.1-2403 as seen from their chemical enrichment

Aims: Environmental effects gain importance as large scalestructures in the Universe develop with time and have become thedominant mechanism for quenching galaxies of intermediate and lowstellar masses at lower redshifts. Therefore clusters of galaxies atz< 0.5 are the sites where environmental effects are expected to bemore pronounced and more easily observed with present-day largetelescopes. Methods: We explore the Frontier Fields cluster MACSJ0416.1-2403 at z = 0.3972 with VIMOS/VLT spectroscopy from theCLASH-VLT survey covering a region that corresponds to almost threevirial radii. We measure fluxes of Hβ [O III]λ 5007Hα and [N II]λ 6584 emission lines of cluster membersenabling us to unambiguously derive O/H gas metallicities and also starformation rates from extinction-corrected Hα fluxes. We compareour cluster galaxy sample with a field sample at z ~ 0.4 drawn fromzCOSMOS. Results: The 76 galaxies of our cluster sample followthe star-forming metallicity sequence in a diagnostic diagramdisentangling ionizing sources. For intermediate masses we find asimilar distribution of cluster and field galaxies in the mass vs.metallicity and mass vs. sSFR diagrams. An in-depth investigationfurthermore reveals that bulge-dominated cluster galaxies have onaverage lower sSFRs and higher O/Hs than their disk-dominatedcounterparts. We use the location of galaxies in the projected velocityvs. position phase-space to separate our cluster sample into a region ofobjects accreted longer ago and a region of recently accreted andinfalling galaxies. We find a higher fraction of accreted metal-richgalaxies (63%) compared to the fraction of 28% of metal-rich galaxies inthe infalling regions. Intermediate-mass galaxies (9.2 < log(M/M_⊙) < 10.2) falling into the cluster for the firsttime are found to be in agreement with predictions of the fundamentalmetallicity relation. In contrast for already accreted star-forminggalaxies of similar masses we find on average metallicities higher thanpredicted by the models. This trend is intensified for accreted clustergalaxies of the lowest mass bin (log (M/M_⊙) < 9.2)that display metallicities two to three times higher than predicted bymodels with primordial gas inflow. Environmental effects thereforestrongly influence gas regulations and control gas metallicities of log(M/M_⊙) < 10.2 cluster galaxies. We also investigatechemical evolutionary paths of model galaxies with and without inflow ofgas showing that strangulation is needed to explain the highermetallicities of accreted cluster galaxies. Our results favor astrangulation scenario in which gas inflow stops for galaxies with log(M/M_⊙) < 10.2 when accreted by the cluster.