7 Summary

• We have covered with H$\alpha$+[NII] and NIR imaging observations $\sim$$60 \%$ of the late-type (spiral) galaxies brighter than m_p=16.0 in the Virgo cluster and in the Coma/A1367 supercluster.
• The H$\alpha$ EW of spiral galaxies shows the expected decrease toward the center of the three studied clusters only when galaxies brighter than -19.5 are considered. Weaker and dwarf systems show no or reverse trends, indicating that substantial infall of small spiral galaxies is currently taking place onto local clusters.
• From the combined H$\alpha$ and NIR data we derive the birthrate, i.e. the fraction of young to old stars, providing an estimate of the star formation history for these galaxies.
• The birthrate parameter shows a weak increasing trend with increasing lateness in the Hubble classification.
• The birthrate parameter of isolated galaxies in the Great Wall is in almost inverse proportionality with the NIR luminosity, i.e. with the systemic mass. Giant spiral galaxies have a ratio of young-to-old stars 100 times lower than their dwarf counterparts.
• A large fraction of spiral galaxies in the Virgo cluster have a birthrate parameter significantly lower (a factor 3) than isolated galaxies of similar luminosity.
• Galaxies with quenched current star formation coincide with galaxies with significant gas deficiency.
• A population of currently star forming galaxies with normal gas content is found projected near the center of the Virgo cluster. Their Tully-Fisher distance is approximately 1 mag larger than the one of the deficient objects, which corresponds with the distance of the M 87 cluster. This points out the existence of a distinct cloud of galaxies falling onto the Virgo cluster.

Acknowledgements

This research has made use of the NASA/IPAC Extragalactic Database (NED) which is operated by the Jet Propulsion Laboratory, California Institute of Technology, under contract with the National Aeronautics and Space Administration.