The Stellar Populations of Stripped Spiral Galaxies in the Virgo Cluster
  (Abridged) We present an analysis of the stellar populations of the gas-stripped outer disks of ten Virgo Cluster spiral galaxies, utilizing SparsePak integral field spectroscopy on the WIYN 3.5m telescope and GALEX UV photometry. The galaxies in our sample show evidence for being gas-stripped spiral galaxies, with star formation within a truncation radius, and a passive population beyond the truncation radius. We find that all of the galaxies with spatially truncated star formation have outer disk stellar populations consistent with star formation ending within the last 500 Myr. The synthesis of optical spectroscopy and GALEX observations demonstrate that star formation was relatively constant until the quenching time, after which the galaxies passively evolved. Large starbursts at the time of quenching are excluded for all galaxies. For approximately half of our galaxies, timescales derived from our observations are consistent with galaxies being stripped in or near the cluster core, where simple ram-pressure estimates can explain the stripping. However, the other half of our sample galaxies were clearly stripped outside the cluster core. Such galaxies provide evidence that the intra-cluster medium is not static and smooth. For three of our sample galaxies, our stripping timescales agree with those from the gas stripping simulations, suggesting that star formation is quenched near the time of peak pressure. While the stripping of star-forming gas in the outer disk creates a passive population in our galaxies, there is still normal star formation in the center of our sample galaxies. It may be that Virgo is not massive enough to completely strip these spiral galaxies and, in a more dynamically active cluster or a cluster with a higher density ICM, such a process would lead to passive spirals and/or S0s. 
Hugh H. Crowl and Jeffrey D.P. Kenney (Yale University)