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A. Dressler (Carnegie Observatories)
The correlation between galaxy type and environment that is called the morphology-density relation has its roots in the early 20th century with Shapley and Hubble, at a time when galaxies themselves were a new subject of study. Today we recognize the morphology-density relation as a manifestation of galaxy evolution, something not within the realm of consideration of these pioneers. However, those who work in this field have yet to agree on whether these remarkably strong correlations reflect processes that occurred early in the history of the universe, or alternatively late in the lives of these galaxies, i.e., galaxy transformation from one type to another. Clearly the best way to resolve this question will be to follow the morphology-density relation back into the past. With the Sloan Digital Sky Survey providing a secure present-day sample, and the increasing availability of higher-redshift cluster and field samples, there are excellent opportunities of charting the development of the morphology- density relationship since redshift z = 1 or even beyond.
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Bulletin of the American Astronomical Society, 36 #2
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