Environmental Effects on Galaxy Evolution Based on the SDSS
  We have constructed a large, uniform galaxy cluster catalog from the Sloan Digital Sky Survey data. By studying the morphology--cluster-centric-radius relation, we have found two characteristic environments where galaxy morphologies change dramatically, indicating there exist two different physical mechanisms responsible for the cluster galaxy evolution. We also found an unusual population of galaxies, which have spiral morphology but do not have any emission lines, indicating these spiral galaxies do not have any on-going star formation activity. More interestingly, these passive spiral galaxies preferentially exist in the cluster outskirts. Therefore, these passive spiral galaxies are likely to be a key galaxy population being transformed from blue, star-forming galaxies into red, early-type galaxies. 
Tomotsugu Goto (JAXA)