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