The Trouble with Hubble Types in the Virgo Cluster

Quantitative measures of central light concentration and star formationactivity are derived from R and Halpha surface photometry of 84 bright S0-ScdVirgo Cluster and isolated spiral galaxies. For isolated spirals, there is agood correlation between these two parameters and assigned Hubble types. In theVirgo Cluster, the correlation between central light concentration and starformation activity is significantly weaker. Virgo Cluster spirals havesystematically reduced global star formation with respect to isolated spirals,with severe reduction in the outer disk, but normal or enhanced activity in theinner disk. Assigned Hubble types are thus inadequate to describe the range inmorphologies of bright Virgo Cluster spirals. In particular, spirals withreduced global star formation activity are often assigned misleading early-typeclassifications, irrespective of their central light concentrations. 45+-25% ofthe galaxies classified as Sa in the Virgo Cluster sample have central lightconcentrations more characteristic of isolated Sb-Sc galaxies. The misleadingclassification of low concentration galaxies with low star formation rates asearly-type spirals may account for part of the excess of `early-type' spiralgalaxies in clusters. Thus the morphology-density relationship is not all dueto a systematic increase in the bulge-to-disk ratio with environmental density.