Star-formation quenching of cluster galaxies as traced by metallicity, presence of active galactic nuclei, and galactic conformity

TL;DR

This study investigates how metallicity, active galactic nuclei, and galactic conformity influence star-formation quenching in cluster galaxies at z~0.2, revealing environmental effects and the role of BCG activity.

Contribution

It provides new insights into the environmental mechanisms affecting star formation and metallicity in cluster galaxies, highlighting the impact of BCG activity on galactic conformity.

Findings

Metallicity of SF galaxies is enhanced in clusters with passive BCGs.

Higher fraction of AGNs and RQGs in clusters with passive BCGs.

Galactic conformity suggests active BCGs sustain their activity over ~1 Gyr.

Abstract

(Abridged) We explored 18 clusters from LoCuSS at z~0.2 with ACReS spectra of ~1800 cluster members at R<R200 in a mass-complete sample. The metallicities of SF cluster galaxies with R<R200 were found to be enhanced with respect to the MZR of coeval field SF galaxies. This metallicity enhancement is limited to lower-mass satellites of the 9 clusters with a passive BCG. Many of the SF galaxies with enhanced metallicities are found in the core regions of the phase-space diagram expected for virialized populations. We find a higher fraction of higher mass SF galaxies at R<R500 in clusters with active BCGs compared to clusters with passive BCGs, a signal for galactic conformity. In contrast, much higher fractions of AGNs and especially recently quenched galaxies (RQGs) at R<R500 are found in clusters with passive BCGs in comparison to clusters with active BCGs. We deduce that strangulation is initiated in clusters with passive BCGs when SF satellite galaxies pass R200, by stopping the pristine gas inflow which would otherwise dilute the ISM and would maintain their metallicities at values similar to those of field galaxies at similar redshifts. For galaxies with higher masses which survived to be SF when travelling to R<R500 of clusters with passive BCGs, we assume that they suffer a rapid quenching of star formation, likely due to AGNs triggered by the increasing RPS toward the cluster center, which can compress the gas and fuel AGNs; these AGNs can rapidly quench and maintain quenched satellite galaxies. On the other hand, we found that surviving SF massive satellite galaxies around active BCGs are less affected by environment when they enter R<R500, since we observe R<R500 SF galaxies with higher masses and with metallicities typical of coeval field galaxies. This observed galactic conformity implies that active BCGs must maintain their activity over timescales of at least ~1Gyr.