Massive Star Formation Rates and Radial Distributions from Hα Imaging of 84 Virgo Cluster and Isolated Spiral Galaxies

The massive star formation properties of 55 Virgo Cluster and 29 isolated S0-Scd bright (M_B<=-18) spiral galaxies are compared via analyses of R and Hα surface photometry and integrated fluxes as functions of Hubble type and central R light concentration (bulge-to-disk ratio). In the median, the total normalized massive star formation rates (NMSFRs) in Virgo Cluster spiral galaxies are reduced by factors of up to 2.5 compared with isolated spiral galaxies of the same type or concentration, with a range from enhanced (up to 2.5 times) to strongly reduced (up to 10 times). Within the inner 30% of the optical disk, Virgo Cluster and isolated spiral galaxies have similar ranges in NMSFRs, with similar to enhanced (up to 4 times) median NMSFRs for Virgo galaxies. NMSFRs in the outer 70% of the optical disk are reduced in the median by factors of up to 9 for Virgo Cluster spiral galaxies, with more severely reduced star formation at progressively larger disk radii. Thus, the reduction in total star formation of Virgo Cluster spiral galaxies is caused primarily by spatial truncation of the star-forming disks. The correlation between H I deficiency and R light central concentration is much weaker than the correlation between H I deficiency and Hubble type. The previously observed systematic difference in H I spatial distributions and kinematics between early- and late-type spiral galaxies in the Virgo Cluster is at least partially due to the misleading classification of stripped spiral galaxies as early types. Intracluster medium-interstellar medium stripping of the gas from spiral galaxies is likely responsible for the truncated star-forming disks of Virgo Cluster spiral galaxies. This effect may be responsible for a significant part of the morphology-density relationship, in that a large fraction of Virgo Cluster galaxies classified as Sa galaxies are H I-deficient galaxies with truncated star-forming disks rather than galaxies with large bulge-to-disk ratios.