The galaxy cluster AC114
Authors: Andrade A. , Saviane I. , Monaco L. , Yegorova I. , Proust D. 
Published: March 2024

Context. The mass-metallicity relation (MZR) is a powerful tool to constrain internal physical processes that drive the chemical evolution of galaxies. However, the construction of this relation is carried out with field star-forming galaxies in big data surveys where environmental effects are either negligible or not studied in detail.

Aims. We study the role of galaxy clusters in the MZR and its evolution at z = 0.317 with star-forming members of AC114 (ABELL S1077). The purpose of this work is to understand how both the environmental effects and dynamical events modify the chemical evolution in this galaxy cluster.

Methods. Spectroscopic VIMOS/VLT data was used to select cluster members and classify the galaxy sample in star-forming and passive galaxies. Gas-phase metallicities were estimated by using the strong-line method O3N2 calibrated on Te-based oxygen abundances. Available optical and near-infrared photometry from DECaLS DR10 and the VIKING DR4 ESO survey was used to derive the stellar mass of the galaxy sample.

Results. AC114 is dominated by passive galaxies located in the central region of the cluster, whereas the star-forming members tend to be located outside this region. The constructed MZR from the latter indicates that star-forming galaxies have a lower metal content than foreground galaxies (spanning redshifts up to z = 0.28), and the same or even lower metallicities with respect to background galaxies (spanning redshifts 0.34–0.70). Additionally, it shows a higher scatter of σ = 0.17 dex, consistent with MZRs of galaxy clusters reported in the literature. The MZR at z = 0.317 is downshifted by 0.19 dex on average with respect to local galaxies. Comparing the AC114-MZR with the field MZR at the same redshift, two galaxies are found to be more metal-rich than the field ones by ∼0.10 dex. Likely as a result of ram-pressure stripping, star-forming galaxies deviate more from the MZR than field galaxies at the same redshift. Star-forming galaxies in the cluster are in general metal-poorer than field galaxies at the same redshfit up to ∼0.22 dex, and show a MZR that is slightly shallower in slope compared with that of field galaxies. With a redshift analysis, three substructures were identified: star-forming galaxies in the main component show a higher scatter of 0.20 dex in metallicity than both the front and back ones, with a scatter of 0.07 and 0.11 dex, respectively. Star-forming galaxies located outside the central region of AC114 are driving the shallower slope of the cluster MZR.

Conclusions. The slightly shallower slope and high scatter of AC114 with respect to foreground and background galaxies in the mass-metallicity plane indicates that galaxies are suffering from environmental and dynamical effects. Ram-pressure stripping and strangulation are likely the main drivers in increasing the metallicities of at least two star-forming members with respect to the field MZR at the same redshift. However, the lower metallicities of the star-forming members, which drive the flatter slope of the AC114-MZR, can be explained by strong metal-poor inflows triggered by galaxy-galaxy interactions. In fact, the downshift reported for these galaxies is consistent with other observations and simulations, as a result of mergers and/or flybys, which dilute the gas-phase metallicities from metal-poor inflows. The mass of a galaxy cluster appears to be a key variable in determining the importance of environmental effects in the evolution of cluster members, where massive galaxy clusters (Mvir > 1015 M⊙) show changes in the slope of the MZR.