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Unformatted text preview: The differences may be clues to how different galaxy types form - in some biassing schemes, for example, ellipticals need stronger peaks than disks. On the other hand, if merging is important, this may tell us about the history of mergers rather than galaxy formation. It does seem to be quite consistent in shape among clusters of galaxies, so that it tells something basic and general about how galaxies have developed. Similar clues are hidden in some of the basic correlations among global galaxy properties involving dynamics - the Tully-Fisher and Faber-Jackson relations. The Tully-Fisher relation, often employed as a distance indicator for spirals, is a tight relation between galaxy absolute magnitude and velocity scale of the disk (for example, at the 20% - of - peak level in an integrated H I profile, with appropriate inclination corrections). There are broad theoretical reasons why such a relation might hold, but no deep understanding at this point. The Faber- Jackson relation was also found empirically, from the fact that elliptical-galaxy luminosity and...
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- Fall '10