摘要：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.
关键词：galaxies: evolution;galaxies: clusters: individual: MACS
J0416.1-2403;galaxies: star formation;galaxies:
abundances;galaxies: structure
