Abstract
Quantitative measures of central light concentration and star formation activity are derived from R and Hα surface photometry of 84 bright S0-Scd Virgo Cluster and isolated spiral galaxies. For isolated spirals, there is a good correlation between these two parameters and assigned Hubble types. In the Virgo Cluster, the correlation between central light concentration and star formation activity is significantly weaker. Virgo Cluster spirals have systematically reduced global star formation with respect to isolated spirals, with severe reduction in the outer disk, but normal or enhanced activity in the inner disk. Assigned Hubble types are thus inadequate to describe the range in morphologies of bright Virgo Cluster spirals. In particular, spirals with reduced global star formation activity are often assigned misleading spiral classifications, irrespective of their central light concentrations; 45%±25% of the galaxies classified as Sa in the Virgo Cluster sample have central light concentrations more characteristic of isolated Sb-Sc galaxies. The misleading classification of low-concentration galaxies with low star formation rates as spirals may account for part of the excess of early-type spiral galaxies in clusters. Thus, the morphology-density relationship is not all due to a systematic increase in the bulge-to-disk ratio with environmental density.
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