Radial Distributions of Star Formation and Gas-phase Metallicity in Spiral–Elliptical Galaxy Pairs

Using integral-field spectroscopy from the fourth-generation Sloan Digital Sky Survey Mapping Nearby Galaxies at Apache Point Observatory, we investigate the radial distributions of the star formation rates (SFRs) and gas-phase metallicities in spiral galaxies that reside in spiral–elliptical (S + E) pairs. Spirals in S + E pairs show suppressed central star formation and elevated metallicities, whereas spirals in spiral–spiral pairs exhibit centrally enhanced star formation and reduced metallicities. The degree of SFR suppression and metallicity enhancement in S + E pairs depends on the masses of the pair members. Spirals with more massive elliptical companions experience stronger star formation suppression and larger increases in metallicity, while lower-mass spirals show more pronounced metallicity enhancement. In addition, within S + E systems, galaxies with asymmetric gas velocity fields display an enhanced SFR and higher metallicities, whereas those with symmetric velocity fields exhibit a clear central suppression. Based on these results, we infer that in S + E pairs, the spiral galaxy experiences suppressed gas accretion once it enters the hot circumgalactic medium of its early-type companion, which leads to the observed decline in star formation activity. When a close encounter takes place, tidal perturbations can compress the remaining cold gas and trigger enhanced star formation, producing rapid chemical enrichment and an associated increase in metallicity.