CLASH-VLT: Strangulation of cluster galaxies in MACS J0416.1-2403 as seen from their chemical enrichment^⋆

¹ University of ViennaDepartment of Astrophysics, Tuerkenschanzstrasse 17, 1180 Vienna, Austria
e-mail: christian.maier@univie.ac.at
² INAF−Osservatorio Astronomico di Trieste, via G. B. Tiepolo 11, 34133 Trieste, Italy
³ Dipartimento di Fisica, Università degli Studi di Trieste, via Tiepolo 11, 34143 Trieste, Italy
⁴ INAF−Osservatorio Astronomico di Capodimonte, via Moiariello 16, 80131 Napoli, Italy
⁵ Dipartimento di Fisica e Scienze della Terra, Università di Ferrara, via Saragat 1, 44122 Ferrara, Italy
⁶ INAF−Istituto di Astrofisica Spaziale e Fisica cosmica (IASF) Milano, via Bassini 15, 20133 Milano, Italy
⁷ Dark Cosmology Centre, Niels Bohr Institute, University of Copenhagen, Juliane Maries Vej 30, 2100 Copenhagen, Denmark

Received: 29 January 2016
Accepted: 18 March 2016

Abstract

Aims. Environmental effects gain importance as large scale structures in the Universe develop with time and have become the dominant mechanism for quenching galaxies of intermediate and low stellar masses at lower redshifts. Therefore, clusters of galaxies at z< 0.5 are the sites where environmental effects are expected to be more pronounced and more easily observed with present-day large telescopes.

Methods. We explore the Frontier Fields cluster MACS J0416.1-2403 at z = 0.3972 with VIMOS/VLT spectroscopy from the CLASH-VLT survey covering a region that corresponds to almost three virial radii. We measure fluxes of Hβ, [O III]λ 5007, Hα, and [N II]λ 6584  emission lines of cluster members enabling us to unambiguously derive O/H gas metallicities, and also star formation rates from extinction-corrected Hα  fluxes. We compare our cluster galaxy sample with a field sample at z ~ 0.4 drawn from zCOSMOS.

Results. The 76 galaxies of our cluster sample follow the star-forming metallicity sequence in a diagnostic diagram disentangling ionizing sources. For intermediate masses we find a similar distribution of cluster and field galaxies in the mass vs. metallicity and mass vs. sSFR diagrams. An in-depth investigation furthermore reveals that bulge-dominated cluster galaxies have on average lower sSFRs and higher O/Hs than their disk-dominated counterparts. We use the location of galaxies in the projected velocity vs. position phase-space to separate our cluster sample into a region of objects accreted longer ago and a region of recently accreted and infalling galaxies. We find a higher fraction of accreted metal-rich galaxies (63%) compared to the fraction of 28% of metal-rich galaxies in the infalling regions. Intermediate-mass galaxies (9.2 < log (M/M_⊙) < 10.2) falling into the cluster for the first time are found to be in agreement with predictions of the fundamental metallicity relation. In contrast, for already accreted star-forming galaxies of similar masses, we find on average metallicities higher than predicted by the models. This trend is intensified for accreted cluster galaxies of the lowest mass bin (log (M/M_⊙) < 9.2), that display metallicities two to three times higher than predicted by models with primordial gas inflow. Environmental effects therefore strongly influence gas regulations and control gas metallicities of log (M/M_⊙) < 10.2 cluster galaxies. We also investigate chemical evolutionary paths of model galaxies with and without inflow of gas showing that strangulation is needed to explain the higher metallicities of accreted cluster galaxies. Our results favor a strangulation scenario in which gas inflow stops for galaxies with log (M/M_⊙) < 10.2 when accreted by the cluster.