Environmental Modulation of Small-scale Galactic Conformity in the Virgo Filaments

Abstract We investigate small-scale color conformity in galaxy groups embedded in the large-scale filaments connected to the Virgo cluster. Using filament member galaxies, extracted from the NASA–Sloan Atlas at z < 0.014, we identify 48 groups with bright ( M r − 5 log h ≤ − 18 mag) hosts and faint ( M r − 5 log h > − 18 mag) companions. We quantify color conformity by comparing the host color with the luminosity-weighted mean companion color. We find a positive host–companion color correlation (slope b = 0.39 ± 0.14), indicating that galactic conformity is already present in the filamentary preprocessing environment. Splitting the sample by normalized filament spine distance, the conformity signal is most pronounced in the filament outskirts ( b = 0.76 ± 0.27) and weaker near the filament spine ( b = 0.40 ± 0.18), accompanied by enhanced blueward scatter of companions around red hosts in the inner filament. Stacked projected phase-space diagrams show that blue companions of red hosts in inner filament groups are modestly more common in recent/intermediate-infall loci than in the virialized region. We suggest that the diluted conformity signal in the inner filament might be driven by recently accreted blue dwarfs near the filament spine. Comparison with Virgo cluster conformity relations from H.-R. Lee et al. shows that the inner filament relation is similar to that in the cluster intermediate region, consistent with the interpretation that cluster conformity may retain a vestige of infalling, preprocessed groups from cosmic filaments.