L. Watson, P. Martini, U. Lisenfeld, M. Wong, T. Boeker, und E. Schinnerer. (2012)cite arxiv:1204.1555Comment: 23 pages, 13 figures, 4 tables. Accepted for publication in ApJ. For a brief video explaining the main results of this paper, see http://www.cfa.harvard.edu/sma/postDocs/.