Chemical abundances in Virgo spiral galaxies. II. Effects of cluster environment

We present new measurements of chemical abundances in H II regions in spiral galaxies of the Virgo cluster and a comparison of Virgo galaxies and field spirals. With these new data there now exist nine Virgo spirals with abundance measurements for at least four H II regions. Our sample of Virgo galaxies ranges from H I deficient objects near the core of the cluster to galaxies with normal H I properties, far from the cluster core. We investigate the relationship between H I disk characteristics and chemical abundances to determine whether dynamical processes that remove gas from the disk, such as ram pressure stripping by the intracluster medium, also affect the chemical abundances. We divide the nine Virgo spirals into three groups of three galaxies each: those with strong H I deficiencies, intermediate cases, and those with no H I deficiencies. The three most H I deficient Virgo spirals have larger mean abundances (0.3 to 0.5 dex in O/H) than the spirals on the periphery of the cluster. This suggests that dynamical processes associated with the cluster environment are more important than cluster membership in determining the current chemical properties of spiral galaxies. There is also weak evidence of shallower abundance gradients in the H I deficient Virgo spirals. We also compare the abundance properties of our Virgo sample to a large sample of field spirals studied by Zaritsky, Kennicutt, & Huchra (1994). Those authors found that the mean abundance of the disk gas increases with increasing maximum circular velocity, increasing luminosity, and decreasing (earlier) Hubble type (but with a large dispersion in the mean abundances and abundance gradients). The dispersion in the properties of field galaxies and the small size of the Virgo sample make it difficult to draw definitive conclusions about any systematic difference between the field and Virgo spirals. Nevertheless, the H I deficient Virgo galaxies have larger mean abundances than field galaxies of comparable luminosity or Hubble type, while the spirals at the periphery of the cluster are indistinguishable from the field galaxies. Simple, illustrative chemical evolution models with infall of metal-poor gas are constructed and compared to models in which the infall is terminated. The models are constrained by comparison with observed gas mass fractions, current star formation rates, and gas consumption times. The model results indicate that the curtailment of infall of metal-poor gas onto cluster core spirals may explain part of the enhanced abundance. However, additional work is needed, particularly modeling of the effects of truncating the outer gaseous disk within the context of models with radial gas transport. The increased abundances in cluster core late-type spirals, relative to field galaxies, may be important in the interpretation of observations of these galaxies. Specifically, we point to possible effects on the Tully-Fisher and Cepheid variable distance determinations and the interpretation of colors in the Butcher-Oemler effect.