CLASH-VLT: Enhancement of (O/H) in z=0.35 RXJ 2248-4431 cluster galaxies

TL;DR

This study investigates the gas metallicities and star formation properties of galaxies in the RXJ 2248-443 cluster at z~0.35, revealing enhanced metallicities in intermediate-mass cluster galaxies likely due to environmental effects like ram pressure stripping.

Contribution

It provides the first detailed comparison of metallicities and star formation in cluster versus field galaxies at this redshift, highlighting environmental impacts on galaxy evolution.

Findings

Cluster and field galaxies follow the star-forming main sequence.

Intermediate-mass cluster galaxies show higher metallicities than field counterparts.

Metallicity enhancement in cluster galaxies suggests ram pressure stripping effects.

Abstract

(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.