Abstract
Aims. Gas-phase metallicities offer insight into the chemical evolution of galaxies as they reflect the recycling of gas through star formation and galactic inflows and outflows. Environmental effects such as star-formation quenching mechanisms play an important role in shaping the evolution of galaxies. Clusters of galaxies at z < 0.5 are expected to be the sites where environmental effects can be clearly observed with present-day telescopes. Methods. We explored the Frontier Fields cluster RX J2248−443 at z = 0.348 with VIMOS/VLT spectroscopy from CLASH-VLT, which covers a central region corresponding to almost 2 virial radii. The fluxes of [OII] λ3727, Hβ, [OIII] λ5007, Hα and [NII] λ6584 emission lines were measured allowing the derivation of (O/H) gas metallicities, star formation rates based on extinction-corrected Hα fluxes, and contamination from active galactic nuclei. We compared our sample of cluster galaxies to a population of field galaxies at similar redshifts. Results. 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 the ionising sources in a galaxy to be disentangled, with only a low number of 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 (log(M/M⊙) < 9.2) 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 “mass complete” bin (which is the intermediate mass bin in this study: 9.2 < log(M/M⊙) < 10.2), show more enhanced metallicities than their field counterparts by a factor of 0.065 dex with a ∼1.8σ significance. 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, namely by a factor of ∼0.12 dex. 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 low- and intermediate-mass cluster galaxies is removed due to ram pressure stripping, leading to an increase in their gas-phase metallicity.
Highlights
The chemical abundances of galaxies are an important tool to study galaxy evolution, as they reflect the complex interplay between star formation, gas outflows through winds and supernovae, and galactic gas inflows
We explored the Frontier Fields cluster RX J2248−443 at z = 0.348 with VIMOS/Very Large Telescope (VLT) spectroscopy from CLASH-VLT, which covers a central region corresponding to almost 2 virial radii
The results of this study demonstrated that galaxies with reliable signs of star formation form an apparent sequence with a limited range of star formation rate (SFR) values at a given stellar mass and redshift and with log(SFR) ∝ M∗
Summary
The chemical abundances of galaxies are an important tool to study galaxy evolution, as they reflect the complex interplay between star formation, gas outflows through winds and supernovae, and galactic gas inflows. Environmental effects are expected to get stronger at z < 0.5 as the large-scale structures of the universe evolve (e.g. Fig. 15 Peng et al 2010), and clusters of galaxies at intermediate redshifts should be the ideal sites to observe these effects, which effectively lead to the quenching of star formation and are to some extent expected to affect the gas metallicities of cluster galaxies Both Pasquali et al (2012) and Peng & Maiolino (2014) studied central and satellite SDSS galaxies and found that the average metallicity of satellite galaxies is higher than that of central galaxies, especially at low stellar masses. We investigate the stellar masses and the AGN contribution, and present the derivation of SFRs and gas-phase metallicities for the 121 cluster and 130 field galaxies that we observe. We note that (gas phase) metallicity and abundance are used to denote oxygen abundance, (O/H), throughout this paper
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